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Room Humidifiers – Health Concerns

CARE OF ROOM HUMIDIFIERS: Dirty Humidifiers May Cause Health Problems

CPSC Document #5046

The U.S. Consumer Product Safety Commission (CPSC) is alerting consumers to possible health hazards resulting from dirty room humidifiers. The CPSC has found that bacteria and fungi often grow in the tanks of portable and console room humidifiers and can be released in the mist. Breathing dirty mist may cause lung problems ranging from flu-like symptoms to serious infection. This information is of special concern to allergy or asthma sufferers whose symptoms may be increased.

Film or scum appearing on the water surface, on the sides or bottom of the tank, or on exposed motor parts may indicate that the humidifier tank contains bacteria or fungi. A crusty deposit or scale may also form within the tank or on parts in the water. This scale is composed of minerals that have settled out of the water creating a surface on which bacteria or fungi may grow.

Minerals can also be released in the mist and settle as fine white dust. This white dust may contain particles that are small enough to enter the lungs. The health effects from inhaling this humidifier dust are not clear, any impact on human health will depend upon the types and amounts of minerals found in the water used.

To reduce the possibility of health hazards from dirty room humidifiers, the staff of the Consumer Product Safety Commission recommends that you take the following precautions:

  • Do not allow film and scale to develop in your humidifier. If possible, change the water in your room humidifier daily. Empty the tank before you fill it. If the tank is not removable, clean it often according to manufacturer’s instructions.
  • Use distilled or demineralized water in your room humidifier to reduce the buildup of scale and the release of dust. Do not use tap water because it contains more minerals. Use demineralization cartridges or filters if supplied or recommended for use with your humidifier.
  • Drain and clean the tank of your room humidifier before you store it. Clean it after summer storage. Remove dust on the outside of your unit.
  • Clean your room humidifier well and often during the heating season. Be sure to unplug the humidifier before cleaning. Follow the manufacturer’s suggested cleaning methods. If chlorine bleach or other cleaning product or disinfectant is used, make sure to rinse the tank well to avoid breathing harmful chemicals. Use a brush or other scrubber to clean the tank. Be careful not to damage the motor or to scratch the inner surface. Clean or replace sponge filters or belts when needed.
  • Maintain the relative humidity in your home between 30% and 50% if possible. Humidity levels above 60% may allow moisture to build up indoors and condense on surfaces, where bacteria and fungi can settle and grow. You can measure humidity with an instrument called a hygrometer, available at your local hardware store.

 Combustion Appliances – Indoor Air Pollution

What You Should Know About Combustion Appliances and Indoor Air Pollution

CPSC Document #452

Hazards may be associated with almost all types of appliances. The purpose of this booklet is to answer some common questions you may have about the potential for one specific type of hazard – indoor air pollution – associated with one class of appliances – combustion appliances.

Combustion appliances are those which burn fuels for warmth, cooking, or decorative purposes. Typical fuels are gas, both natural and liquefied petroleum (LP); kerosene; oil; coal; and wood. Examples of the appliances are space heaters, ranges, ovens, stoves, furnaces, fireplaces, water heaters, and clothes dryers. These appliances are usually safe. However, under certain conditions, these appliances can produce combustion pollutants that can damage your health, or even kill you.

POSSIBLE HEALTH EFFECTS range from headaches, dizziness, sleepiness, and watery eyes to breathing difficulties or even death. Similar effects may also occur because of common medical problems or other indoor air pollutants.

This booklet was written:

  1. to encourage the proper use, maintenance, and installation of combustion appliances;
  2. to discuss the pollutants produced by these appliances;
  3. to describe how these pollutants can affect your health; and,
  4. to tell you how you can reduce your exposure to them.

Should I be concerned about indoor air pollution?

YES. Studies have shown that the air in our homes can be even more polluted than the outdoor air in big cities. Because people spend a lot of time indoors, the quality of the air indoors can affect their health. Infants, young children and the elderly are a group shown to be more susceptible to pollutants. People with chronic respiratory or cardiovascular illness or immune system diseases are also more susceptible than others to pollutants.

Many factors determine whether pollutants in your home will affect your health. They include the presence, use, and condition of pollutant sources, the level of pollutants both indoors and out, the amount of ventilation in your home, and your overall health.

Most homes have more than one source of indoor air pollution. For example, pollutants come from tobacco smoke, building materials, decorating products, home furnishings, and activities such as cooking, heating, cooling, and cleaning. Living in areas with high outdoor levels of pollutants usually results in high indoor levels. Combustion pollutants are one category of indoor air pollutants.

What are combustion pollutants?

Combustion pollutants are gases or particles that come from burning materials. The combustion pollutants discussed in this booklet come from burning fuels in appliances. The common fuels burned in these appliances are natural or LP gas, fuel oil, kerosene, wood, or coal. The types and amounts of pollutants produced depend upon the type of appliance, how well the appliance is installed, maintained, and vented, and the kind of fuel it uses. Some of the common pollutants produced from burning these fuels are carbon monoxide, nitrogen dioxide, particles, and sulfur dioxide. Particles can have hazardous chemicals attached to them. Other pollutants that can be produced by some appliances are unburned hydrocarbons and aldehydes.

Combustion always produces water vapor. Water vapor is not usually considered a pollutant, but it can act as one. It can result in high humidity and wet surfaces. These conditions encourage the growth of biological pollutants such as house dust mites, molds, and bacteria.

Where do combustion pollutants come from?

Combustion pollutants found indoors include: outdoor air, tobacco smoke, exhaust from car and lawn mower internal combustion engines, and some hobby activities such as welding, woodburning, and soldering. Combustion pollutants can also come from vented or unvented combustion appliances. These appliances include space heaters, gas ranges and ovens, furnaces, gas water heaters, gas clothes dryers, wood or coal-burning stoves, and fireplaces. As a group these are called “combustion appliances.”

What is a vented appliance?

Vented appliances are appliances designed to be used with a duct, chimney, pipe, or other device that carry the combustion pollutants outside the home. These appliances can release large amounts of pollutants directly into your home, if a vent is not properly installed, or is blocked or leaking.

What is an unvented appliance?

Unvented appliances do not vent to the outside, so they release combustion pollutants directly into the home.

Look at the box below for typical appliance problems that cause the release of pollutants in your home. Many of these problems are hard for a homeowner to identify. A professional is needed.


Appliances Fuel Typical Potential Problems
Central Furnaces
Room Heaters
Natural or
Petroleum Gas
Cracked heat exchanger;
Not enough air to burn fuel properly; Defective/blocked flue; Maladjusted burner
Central Furnaces Oil Cracked heat exchanger;
Not enough air to burn fuel properly;
Defective/blocked flue; Maladjusted burner
Central Heaters
Room Heaters
Wood Cracked heat exchanger; Not enough air to burn fuel properly; Defective/blocked flue; Green or treated wood
Central Furnaces
Coal Cracked heat exchanger; Not enough air to burn fuel properly; Defective grate
Room Heaters
Central Heaters
Kerosene Improper adjustment; Wrong fuel (not-K-1); Wrong wick or wick height; Not enough air to burn fuel properly
Water Heaters Natural or
Petroleum Gas
Not enough air to burn fuel properly; Defective/blocked flue; Maladjusted burner
Ranges; Ovens Natural or
Petroleum Gas
Not enough air to burn fuel properly; Maladjusted burner; Misuse as a room heater
Not enough air to burn fuel properly; Defective/blocked flue; Green or treated wood; Cracked heat exchanger or firebox

Can I use charcoal grills or charcoal hibachis indoors?

No. Never use these appliances inside homes, trailers, truck-caps, or tents. Carbon monoxide from burning and smoldering charcoal can kill you if you use it indoors for cooking or heating. There are about 25 deaths each year from the use of charcoal grills and hibachis indoors.

NEVER burn charcoal inside homes, trailers, tents, or other enclosures. The carbon monoxide can kill you.

What are the health effects of combustion pollutants?

The health effects of combustion pollutants range from headaches and breathing difficulties to death. The health effects may show up immediately after exposure or occur after being exposed to the pollutants for a long time. The effects depend upon the type and amount of pollutants and the length of time of exposure to them. They also depend upon several factors related to the exposed person. These include the age and any existing health problems. There are still some questions about the level of pollutants or the period of exposure needed to produce specific health effects. Further studies to better define the release of pollutants from combustion appliances and their health effects are needed.

The sections below discuss health problems associated with some common combustion pollutants. These pollutants include carbon monoxide, nitrogen dioxide, particles, and sulfur dioxide. Even if you are healthy, high levels of carbon monoxide can kill you within a short time. The health effects of the other pollutants are generally more subtle and are more likely to affect susceptible people. It is always a good idea to reduce exposure to combustion pollutants by using and maintaining combustion appliances properly.

Carbon Monoxide:

Each year, according to CPSC, there are more than 200 carbon monoxide deaths related to the use of all types of combustion appliances in the home. Exposure to carbon monoxide reduces the blood’s ability to carry oxygen. Often a person or an entire family may not recognize that carbon monoxide is poisoning them. The chemical is odorless and some of the symptoms are similar to common illnesses. This is particularly dangerous because carbon monoxide’s deadly effects will not be recognized until it is too late to take action against them.

Carbon monoxide exposures especially affect unborn babies, infants, and people with anemia or a history of heart disease. Breathing low levels of the chemical can cause fatigue and increase chest pain in people with chronic heart disease. Breathing higher levels of carbon monoxide causes symptoms such as headaches, dizziness, and weakness in healthy people. Carbon monoxide also causes sleepiness, nausea, vomiting, confusion, and disorientation. At very high levels it causes loss of consciousness and death.

Nitrogen Dioxide:

Breathing high levels of nitrogen dioxide causes irritation of the respiratory tract and causes shortness of breath. Compared to healthy people, children, and inpiduals with respiratory illnesses such as asthma, may be more susceptible to the effects of nitrogen dioxide.

Some studies have shown that children may have more colds and flu when exposed to low levels of nitrogen dioxide. When people with asthma inhale low levels of nitrogen dioxide while exercising, their lung airways can narrow and react more to inhaled materials.


Particles suspended in the air can cause eye, nose, throat, and lung irritation. They can increase respiratory symptoms, especially in people with chronic lung disease or heart problems. Certain chemicals attached to particles may cause lung cancer, if they are inhaled. The risk of lung cancer increases with the amount and length of exposure. The health effects from inhaling particles depend upon many factors, including the size of the particle and its chemical make-up.

Sulfur Dioxide:

Sulfur dioxide at low levels of exposure can cause eye, nose, and respiratory tract irritation. At high exposure levels, it causes the lung airways to narrow. This causes wheezing, chest tightness, or breathing problems. People with asthma are particularly susceptible to the effects of sulfur dioxide. They may have symptoms at levels that are much lower than the rest of the population.

Other Pollutants:

Combustion may release other pollutants. They include unburned hydrocarbons and aldehydes. Little is known about the levels of these pollutants in indoor air and the resulting health effects.

What do I do if I suspect that combustion pollutants are affecting my health?

If you suspect you are being subjected to carbon monoxide poisoning get fresh air immediately. Open windows and doors for more ventilation, turn off any combustion appliances, and leave the house. You could lose consciousness and die from carbon monoxide poisoning if you do nothing. It is also important to contact a doctor IMMEDIATELY for a proper diagnosis. Remember to tell your doctor that you suspect carbon monoxide poisoning is causing your problems. Prompt medical attention is important.

Remember that some symptoms from combustion pollutants – headaches, dizziness, sleepiness, coughing, and watery eyes – may also occur because of common medical problems. These medical problems include colds, the flu, or allergies. Similar symptoms may also occur because of other indoor air pollutants. Contact your doctor for a proper diagnosis.

To help your doctor make the correct diagnosis, try to have answers to the following questions:

  • Do your symptoms occur only in the home? Do they disappear or decrease when you leave home, and reappear when you return?
  • Is anyone else in your household complaining of similar symptoms, such as headaches, dizziness, or sleepiness? Are they complaining of nausea, watery eyes, coughing, or nose and throat irritation?
  • Do you always have symptoms?
  • Are your symptoms getting worse?
  • Do you often catch colds or get the flu?
  • Are you using any combustion appliances in your home?
  • Has anyone inspected your appliances lately? Are you certain they are working properly?

Your doctor may take a blood sample to measure the level of carbon monoxide in your blood if he or she suspects carbon monoxide poisoning. This sample will help determine whether carbon monoxide is affecting your health.

Contact qualified appliance service people to have your appliances inspected and adjusted if needed. You should be able to find a qualified person by asking your appliance distributor or your fuel supplier. In some areas, the local fuel company may be able to inspect and adjust the appliance.

How can I reduce my exposure to combustion pollutants?

Proper selection, installation, inspection and maintenance of your appliances are extremely important in reducing your exposure to these pollutants. Providing good ventilation in your home and correctly using your appliance can also reduce your exposure to these pollutants.

Additionally, there are several different residential carbon monoxide detectors for sale. The CPSC is encouraging the development of detectors that will provide maximum protection. These detectors would warn consumers of harmful carbon monoxide levels in the home. They may soon be widely available to reduce deaths from carbon monoxide poisoning.


  • Choose vented appliances whenever possible.
  • Only buy combustion appliances that have been tested and certified to meet current safety standards. Examples of certifying organizations are Underwriters Laboratories (UL) and the American Gas Association (AGA) Laboratories. Look for a label that clearly shows the certification.
  • All currently manufactured vented gas heaters are required by industry safety standards to have a safety shut-off device. This device helps protect you from carbon monoxide poisoning by shutting off an improperly vented heater.
  • Check your local and state building codes and fire ordinances to see if you can use an unvented space heater, if you consider purchasing one. They are not allowed to be used in some communities, dwellings, or certain rooms in the house.
  • If you must replace an unvented gas space heater with another, make it a new one. Heaters made after 1982 have a pilot light safety system called an oxygen depletion sensor (ODS). This system shuts off the heater when there is not enough fresh air, before the heater begins producing large amounts of carbon monoxide. Look for the label that tells you that the appliance has this safety system. Older heaters will not have this protection system.
  • Consider buying gas appliances that have electronic ignitions rather than pilot lights. These appliances are usually more energy efficient and eliminate the continuous low-level pollutants from pilot lights.
  • Buy appliances that are the correct size for the area you want to heat. Using the wrong size heater may produce more pollutants in your home and is not an efficient use of energy.
  • Talk to your dealer to determine the type and size of appliance you will need. You may wish to write to the appliance manufacturer or association for more information on the appliance. Some addresses are in the back of this booklet.
  • All new woodstoves are EPA-certified to limit the amounts of pollutants released into the outdoor air. For more information on selecting, installing, operating, and maintaining woodburning stoves, write to the EPA Wood Heater Program. Their address is at the bottom of this booklet. Before buying a woodstove check your local laws about the installation and use of woodstoves.

Proper Installation

You should have your appliances professionally installed. Professionals should follow the installation directions and applicable building codes. Improperly installed appliances can release dangerous pollutants in your home and may create a fire hazard. Be sure that the installer checks for backdrafting on all vented appliances. A qualified installer knows how to do this.


  • To reduce indoor air pollution, a good supply of fresh outdoor air is needed. The movement of air into and out of your home is very important. Normally, air comes through cracks around doors and windows. This air helps reduce the level of pollutants indoors. This supply of fresh air is also important to help carry pollutants up the chimney, stovepipe, or flue to the outside.
  • Keep doors open to the rest of the house from the room where you are using an unvented gas space heater or kerosene heater, and crack open a window. This allows enough air for proper combustion and reduces the level of pollutants, especially carbon monoxide.
  • Use a hood fan, if you are using a range. They reduce the level of pollutants you breath, if they exhaust to the outside. Make sure that enough air is coming into the house when you use an exhaust fan. If needed, slightly open a door or window, especially if other appliances are in use. For proper operation of most combustion appliances and their venting system, the air pressure in the house should be greater than that outside. If not, the vented appliances could release combustion pollutants into the house rather than outdoors. If you suspect that you have this problem you may need the help of a qualified person to solve it.
  • Make sure that your vented appliance has the vent connected and that nothing is blocking it. Make sure there are no holes or cracks in the vent. Do not vent gas clothes dryers or water heaters into the house for heating. This is unsafe.
  • Open the stove’s damper when adding wood. This allows more air into the stove. More air helps the wood burn properly and prevents pollutants from being drawn back into the house instead of going up the chimney. Visible smoke or a constant smoky odor inside the home when using a woodburning stove is a sign that the stove is not working properly. Soot on furniture in the rooms where you are using the stove also tells this. Smoke and soot are signs that the stove is releasing pollutants into the indoor air.

Correct Use

  • Read and follow the instructions for all appliances so you understand how they work. Keep the owner’s manual in a convenient place to refer to when needed. Also, read and follow the warning labels because they tell you important safety information that you need to know. Reading and following the instructions and warning labels could save your life.
  • Always use the correct fuel for the appliance.
  • Only use water-clear ASTM 1-K kerosene for kerosene heaters. The use of kerosene other than 1-K could lead to a release of more pollutants in your home. Never use gasoline in a kerosene heater because it can cause a fire or an explosion. Using even small amounts of gasoline could cause a fire.
  • Use seasoned hardwoods (elm, maple, oak) instead of softwoods (cedar, fir, pine) in woodburning stoves and fireplaces. Hardwoods are better because they burn hotter and form less creosote, an oily, black tar that sticks to chimneys and stove pipes. Do not use green or wet woods as the primary wood because they make more creosote and smoke. Never burn painted scrap wood or wood treated with preservatives, because they could release highly toxic pollutants, such as arsenic or lead. Plastics, charcoal, and colored paper such as comics, also produce pollutants. Never burn anything that the stove or fireplace manufacturer does not recommend.
  • Never use a range, oven, or dryer to heat your home. When you misuse gas appliances in this way, they can produce fatal amounts of carbon monoxide. They can produce high levels of nitrogen dioxide, too.
  • Never use an unvented combustion heater overnight or in a room where you are sleeping. Carbon monoxide from combustion heaters can reach dangerous levels.
  • Never ignore a safety device when it shuts off an appliance. It means that something is wrong. Read your appliance instructions to find out what you should do or have a professional check out the problem.
  • Never ignore the smell of fuel. This usually indicates that the appliance is not operating properly or is leaking fuel. Leaking fuel will not always be defectible by smell. If you suspect that you have a fuel leak have it fixed as soon as possible. In most cases you should shut off the appliance, extinguish any other flames or pilot lights, shut off other appliances in the area, open windows and doors, call for help, and leave the area.

Inspection and Maintenance

  • Have your combustion appliance regularly inspected and maintained to reduce your exposure to pollutants. Appliances that are not working properly can release harmful and even fatal amounts of pollutants, especially carbon monoxide.
  • Have chimneys and vents inspected when installing or changing vented heating appliances. Some modifications may be required. For example, if a change was made in your heating system from oil to natural gas, the flue gas produced by the gas system could be hot enough to melt accumulated oil combustion debris in the chimney or vent. This debris could block the vent forcing pollutants into the house. It is important to clean your chimney and vents especially when changing heating systems.

What are the inspection and maintenance procedures?

The best advice is to follow the recommendations of the manufacturer. The same combustion appliance may have different inspection and maintenance requirements, depending upon where you live.

In general, check the flame in the furnace combustion chamber at the beginning of the heating season. Natural gas furnaces should have a blue flame with perhaps only a slight yellow tip. Call your appliance service representative to adjust the burner if there is a lot of yellow in the flame, or call your local utility company for this service. LP units should have a flame with a bright blue center that may have a light yellow tip. Pilot lights on gas water heaters and gas cooking appliances should also have a blue flame. Have a trained service representative adjust the pilot light if it is yellow or orange.

Before each heating season, have flues and chimneys inspected and cleaned before each heating season for leakage and for blockage by creosote or debris. Creosote buildup or leakage could cause black stains on the outside of the chimney or flue. These stains can mean that pollutants are leaking into the house.

The chart below shows how and when to take care of your appliance.

This booklet discussed the types of pollutants that may be produced by combustion appliances, described how they might affect your health, and suggested ways you could reduce your exposure to them. It also explained that proper appliance selection, installation, operation, inspection, and maintenance are very important in reducing exposure to combustion pollutants.


Appliance Inspection/Frequency Maintenance/Frequency
Gas Hot Air Heating System Air Filters – Clean/change filter – Monthly As needed;
Look at flues for rust and soot – Yearly
Qualified person check/clean chimney, clean/adjust burners, check heat exchanger and operation – Yearly (at start of heating season)
Gas/Oil Water/Steam Heating Systems and Water Heaters Look at flues for rust and soot – Yearly Qualified person check/clean chimney, clean combustion chamber, adjust burners, check operation – Yearly (at start of heating season)
Kerosene Space Heaters Look to see that mantle is properly seated – daily when in use;
Look to see that fuel tank is free of water and other contaminants — daily or before refueling
Check and replace wick — Yearly (at start of heating season);
Clean Combustion chamber — Yearly (at start of heating season);
Drain fuel tank — Yearly (at end of heating season)
Wood/Coal Stoves Look at flues for rust and soot – Yearly Qualified person check/clean chimney, check seams and gaskets,
check operation — Yearly (at start of heating season)

 Controlling Indoor Air Pollution

Methods of Controlling Indoor Air Pollution

The three most common approaches to reducing indoor air pollution, in order of effectiveness, are:

  1. Source Control: Eliminate or control the sources of pollution;
  2. Ventilation: Dilute and exhaust pollutants through outdoor air ventilation, and
  3. Air Cleaning: Remove pollutants through proven air cleaning methods.

Of the three, the first approach — source control — is the most effective. This involves minimizing the use of products and materials that cause indoor pollution, employing good hygiene practices to minimize biological contaminants (including the control of humidity and moisture, and occasional cleaning and disinfection of wet or moist surfaces), and using good housekeeping practices to control particles.

The second approach — outdoor air ventilation — is also effective and commonly employed. Ventilation methods include installing an exhaust fan close to the source of contaminants, increasing outdoor air flows in mechanical ventilation systems, and opening windows, especially when pollutant sources are in use.

The third approach — air cleaning — is not generally regarded as sufficient in itself, but is sometimes used to supplement source control and ventilation. Air filters, electronic particle air cleaners and ionizers are often used to remove airborne particles, and gas adsorbing material is sometimes used to remove gaseous contaminants when source control and ventilation are inadequate.

Three Basic Strategies

Source Control

Usually the most effective way to improve indoor air quality is to eliminate inpidual sources of pollution or to reduce their emissions. Some sources, like those that contain asbestos, can be sealed or enclosed; others, like gas stoves, can be adjusted to decrease the amount of emissions. In many cases, source control is also a more cost-efficient approach to protecting indoor air quality than increasing ventilation because increasing ventilation can increase energy costs. Specific sources of indoor air pollution in your home are listed later in this section.

Ventilation Improvements

Another approach to lowering the concentrations of indoor air pollutants in your home is to increase the amount of outdoor air coming indoors. Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Opening windows and doors, operating window or attic fans, when the weather permits, or running a window air conditioner with the vent control open increases the outdoor ventilation rate. Local bathroom or kitchen fans that exhaust outdoors remove contaminants directly from the room where the fan is located and also increase the outdoor air ventilation rate.

It is particularly important to take as many of these steps as possible while you are involved in short-term activities that can generate high levels of pollutants–for example, painting, paint stripping, heating with kerosene heaters, cooking, or engaging in maintenance and hobby activities such as welding, soldering, or sanding. You might also choose to do some of these activities outdoors, if you can and if weather permits.

Advanced designs of new homes are starting to feature mechanical systems that bring outdoor air into the home. Some of these designs include energy-efficient heat recovery ventilators (also known as air-to-air heat exchangers).

  • For more information about air-to-air heat exchangers, contact the U.S. Department of Energy’s Energy Efficiency and Renewable Energy’s Office (EERE) at You may contact the EERE Information Center with questions on EERE’s products, services, and 11 technology programs by calling 1-877-EERE-INF (1-877-337-3463).

Air Cleaners

There are many types and sizes of air cleaners on the market, ranging from relatively inexpensive table-top models to sophisticated and expensive whole-house systems. Some air cleaners are highly effective at particle removal, while others, including most table-top models, are much less so. Air cleaners are generally not designed to remove gaseous pollutants.

The effectiveness of an air cleaner depends on how well it collects pollutants from indoor air (expressed as a percentage efficiency rate) and how much air it draws through the cleaning or filtering element (expressed in cubic feet per minute). A very efficient collector with a low air-circulation rate will not be effective, nor will a cleaner with a high air-circulation rate but a less efficient collector. The long-term performance of any air cleaner depends on maintaining it according to the manufacturer’s directions.

Another important factor in determining the effectiveness of an air cleaner is the strength of the pollutant source. Table-top air cleaners, in particular, may not remove satisfactory amounts of pollutants from strong nearby sources. People with a sensitivity to particular sources may find that air cleaners are helpful only in conjunction with concerted efforts to remove the source.

Over the past few years, there has been some publicity suggesting that houseplants have been shown to reduce levels of some chemicals in laboratory experiments. There is currently no evidence, however, that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices. Indoor houseplants should not be over-watered because overly damp soil may promote the growth of microorganisms which can affect allergic inpiduals.

At present, EPA does not recommend using air cleaners to reduce levels of radon and its decay products. The effectiveness of these devices is uncertain because they only partially remove the radon decay products and do not diminish the amount of radon entering the home. EPA plans to do additional research on whether air cleaners are, or could become, a reliable means of reducing the health risk from radon. EPA’s booklet, Residential Air-Cleaning Devices, provides further information on air-cleaning devices to reduce indoor air pollutants.

For most indoor air quality problems in the home, source control is the most effective solution. This section takes a source-by-source look at the most common indoor air pollutants, their potential health effects, and ways to reduce levels in the home. (For a summary of the points made in this section, see the section entitled “Reference Guide to Major Indoor Air Pollutants in the Home“).

  • Ozone Generators That Are Sold As Air Cleaners (which is only available via this web site) was prepared by EPA to provide accurate information regarding the use of ozone-generating devices in indoor occupied spaces. This information is based on the most credible scientific evidence currently available.

 FAQs about Radon

1) How does radon get into your home?

Any home may have a radon problem.

Radon is a radioactive gas. It comes from the natural decay of uranium that is found in nearly all soils. It typically moves up through the ground to the air above and into your home through cracks and other holes in the foundation. Your home traps radon inside, where it can build up. Any home may have a radon problem. This means new and old homes, well-sealed and drafty homes, and homes with or without basements.

Radon from soil gas is the main cause of radon problems. Sometimes radon enters the home through well water (see “Radon in Water” below). In a small number of homes, the building materials can give off radon, too. However, building materials rarely cause radon problems by themselves.

2) How can you find a qualified radon service provider in your area?

If you are interested in finding a qualified radon service professional to test or mitigate your home, or you need to purchase or have questions about a radon measurement device, you should:

  1. Contact your State Radon Contact (go to and click on your state to get contact information) to determine what are, or whether there are, requirements associated with providing radon measurement and or radon mitigations/reductions in your State. Some States maintain lists of contractors available in their state or they have proficiency programs or requirements of their own.
  2. Contact one or both of the two privately-run National Radon Proficiency Programs (listed below alphabetically) who are offering proficiency listing/accreditation/certification in radon testing and mitigation.

The National Environmental Health Association (NEHA)
National Radon Proficiency Program
Toll Free: (800) 269-4174 or (828) 890-4117
Fax: (828) 890-4161
E-Mail Address:

The National Radon Safety Board (NRSB)
Toll Free: (866) 329-3474
Fax: (914) 345-1169
E-mail Address:

3) What is the average level of radon found in homes in the U.S.?

Based on a national residential radon survey completed in 1991, the average indoor radon level is about 1.3 picocuries per liter (pCi/L) in the United States. The average outdoor level is about 0.4 pCi/L.

4) What are the health effects from exposure to radon?

There are no immediate symptoms from exposures to radon. Based on an updated Assessment of Risk for Radon in Homes (see, radon in indoor air is estimated to cause about 21,000 lung cancer deaths each year in the United States. Smokers are at higher risk of developing Radon-induced lung cancer. Lung cancer is the only health effect which has been definitively linked with radon exposure. Lung cancer would usually occur years (5-25) after exposure. There is no evidence that other respiratory diseases, such as asthma, are caused by radon exposure and there is no evidence that children are at any greater risk of radon induced lung cancer than adults.

5) Where does radon come from?

Radon-222 is the decay product of radium-226. Radon-222 and its parent, radium-226, are part of the long decay chain for uranium-238. Since uranium is essentially ubiquitous (being or seeming to be everywhere at the same time) in the earth’s crust, radium-226 and radon-222 are present in almost all rock and all soil and water.

The amount of radon in the soil depends on soil chemistry, which varies from one house to the next. Radon levels in the soil range from a few hundred to several thousands of pCi/L (pico Curries per Liter). The amount of radon that escapes from the soil to enter the house depends on the weather, soil porosity, soil moisture, and the suction within the house.

6) What is the debate on radon?

There is no debate about radon being a lung carcinogen in humans. All major national and international organizations that have examined the health risks of radon agree that it is a lung carcinogen. The scientific community continues to conduct research to refine our understanding of the precise number of deaths attributable to radon. The National Academy of Sciences BEIR VI Report has estimated that radon causes about 15,000 to 22,000 lung cancer deaths annually based on their two-preferred models. Major scientific organizations continue to believe that approximately 12% of lung cancers annually in the United States are attributable to radon.

7) What is Radon?

Radon is a gaseous radioactive element having the symbol Rn, the atomic number 86, an atomic weight of 222, a melting point of -71ºC, a boiling point of -62ºC, and (depending on the source, there are between 20 and 25 isotopes of radon – 20 cited in the chemical summary, 25 listed in the table of isotopes); it is an extremely toxic, colorless gas; it can be condensed to a transparent liquid and to an opaque, glowing solid; it is derived from the radioactive decay of radium and is used in cancer treatment, as a tracer in leak detection, and in radiography. (From the word radium, the substance from which it is derived.)

Sources: Condensed Chemical Dictionary, and Handbook of Chemistry and Physics, 69th ed., CRC Press, Boca Raton, FL, 1988.

8) Are we sure that radon is a health risk?

EPA already has a wealth of scientific data on the relationship between radon exposure and the development of lung cancer. The scientific experts agree that the occupational miner data is a very solid base from which to estimate risk of lung cancer deaths annually. While residential radon epidemiology studies will improve what we know about radon, they will not supersede the occupational data. Health authorities like the Centers for Disease Control (CDC), the Surgeon General , the American Lung Association, the American Medical Association, and others agree that we know enough now to recommend radon testing and to encourage public action when levels are above 4 pCi/L. The most comprehensive of these efforts has been the National Academy of Science’s Biological Effects of Ionizing Radiation (BEIR VI) Report (see This report reinforces that radon is the second-leading cause of lung cancer and is a serious public health problem. As in the case of cigarette smoking, it would probably take many years and rigorous scientific research to produce the composite data needed to make an even more definitive conclusion.

9) What about radon in schools?

Radon problems in schools are often remedied by increasing the ventilation. However, this will not necessarily remedy an IAQ problem. Some indoor pollution issues cannot be corrected by increasing ventilation. Increasing the ventilation in areas with high humidity or elevated outdoor air pollutants may, in fact, make an existing IAQ problem worse.

10) How do we know radon is a carcinogen?

The World Health Organization (WHO), the National Academy of Sciences, the US Department of Health and Human Services, as well as EPA, have classified radon as a known human carcinogen, because of the wealth of biological and epidemiological evidence and data showing the connection between exposure to radon and lung cancer in humans.

There have been many studies conducted by many different organizations in many nations around the world to examine the relationship of radon exposure and human lung cancer. The largest and most recent of these was an international study, led by the National Cancer Institute (NCI), which examined the data on 68,000 underground miners who were exposed to a wide range of radon levels. The studies of miners are very useful because the subjects are humans, not rats, as in many cancer research studies. These miners are dying of lung cancer at 5 times the rate expected for the general population. Over many years scientists around the world have conducted exhaustive research to verify the cause-effect relationship between radon exposure and the observed increased lung cancer deaths in these miners and to eliminate other possible causes.

In addition, there is an overlap between radon exposures received by miners who got lung cancer and the exposures people would receive over their lifetime in a home at EPA’s action level of 4 pCi/L (pico Curries per Liter), i.e., the lung cancer risk in miners has been documented at exposure levels comparable to those which occur in homes/residences.

11) How do I know if my radon mitigation system is working properly?

There are several methods that a contractor can use to lower radon levels in your home. Some techniques prevent radon from entering your home while others reduce radon levels after it has entered. EPA generally recommends methods which prevent the entry of radon. Soil suction, for example, prevents radon from entering your home by drawing the radon from below the house and venting it through a pipe, or pipes, to the air above the house where it is quickly diluted.

We offer some tips on what to look for to check the contractor’s work at Checking Your Contractors Work

Similar to a furnace or chimney, radon reduction systems need some occasional maintenance. You should look at your warning device on a regular basis to make sure the system is working correctly. Fans may last for five years or more (manufacturer warranties tend not to exceed five years) and may then need to be repaired or replaced. Replacing a fan will cost around $200 – $350 including parts and labor. It is a good idea to retest your home at least every two years to be sure radon levels remain low.

 Radon Risk Assessment Fact Sheet

  • EPA’s indoor radon program promotes voluntary public actions to reduce the risks from indoor radon. EPA and the U.S. Surgeon General recommend that people do a simple home test and if high levels of radon are confirmed, reduce those high levels with straight-forward techniques.
  • EPA recently completed an updated assessment of the Agency’s estimates of lung cancer risks from indoor radon. This assessment reinforces EPA’s recommendations on radon that homeowners should still test and fix their homes for radon.
  • Found all over the U.S., radon is a naturally occurring radioactive gas without color, odor, or taste that comes from the radioactive decay of uranium in soil, rock, and groundwater. It emits ionizing radiation during its radioactive decay to several radioactive isotopes known as radon decay products.
  • Radon gets into the indoor air primarily from soil under homes and other buildings. Radon is a known human lung carcinogen and is the largest source of radiation exposure and risk to the general public. Most inhaled radon is rapidly exhaled, but the inhaled decay products readily deposit in the lung, where they irradiate sensitive cells in the airways increasing the risk of lung cancer.
  • EPA updated the Agency’s estimates of lung cancer risks from indoor radon based on the National Academy of Sciences’ (NAS) latest report on radon, the Biological Effects of Ionizing Radiation (BEIR) VI Report (1999). This report is the most comprehensive review of scientific data gathered on radon and builds on and updates the findings of the previous NAS BEIR IV Report (1988). NAS concluded that the findings of BEIR VI showed that if homeowners haven’t yet tested their homes for radon and fixed them if the levels are elevated, they should do so.
  • The NAS BEIR VI Report confirmed EPA’s long-held position that radon is the second leading cause of lung cancer and a serious public health problem. NAS estimated that radon causes about 20,000 lung cancer deaths each year. The report found that even very small exposures to radon can result in lung cancer and concluded that no evidence exists that shows a threshold of exposure below which radon levels are harmless. The report also concludes that many smokers will get lung cancer due to their radon exposure who otherwise would not have gotten lung cancer. This is because of the synergistic relationship between radon and cigarette smoking in causing lung cancer.
  • To update EPA’s previous risk estimates, EPA worked closely with the Agency’s Science Advisory Board (SAB), an independent panel of scientific experts, to determine how best to apply the various risk models developed by the BEIR VI committee. EPA incorporated the SAB’s advice and recommendations for modifying and extending the methods and approaches used in BEIR VI and constructed a single model yielding results midway between the results obtained using the two models preferred by the BEIR VI committee. These adjustments did not result in significant changes to the BEIR VI risk estimates.
  • EPA’s updated calculation of a best estimate of annual lung cancer deaths from radon is about 21,000 (with an uncertainty range of 8,000 to 45,000) and is consistent with the estimates of the BEIR VI Report. [EPA’s previous best estimate of annual lung cancer deaths from inhaled radon was based on the earlier BEIR IV Report and was about 14,000 (with an uncertainty range of 7,000 to 30,000).]
  • The SAB-endorsed modifications included applying the Agency’s definition of excess risk that includes all radon-induced lung cancer deaths, rather than excluding premature deaths caused by radon in people who would otherwise have eventually died of lung cancer. EPA also used more detailed smoking prevalence data and more recent mortality data to calculate risks than were used by the BEIR VI committee. EPA also calculated numerical estimates of the risk per unit exposure [lung cancer deaths per working level month (WLM)], whereas BEIR VI estimated the fractional increase in lung cancers due to radon.

 Biological Pollutants in Your Home

Biological Pollutants in Your Home

CPSC Document #425

This information will help you understand:

  1. what indoor biological pollution is
  2. whether your home or lifestyle promotes its development
  3. how to control its growth and buildup.

Outdoor air pollution in cities is a major health problem. Much effort and money continues to be spent cleaning up pollution in the outdoor air. But air pollution can be a problem where you least expect it, in the place you may have thought was safest — your home. Many ordinary activities such as cooking, heating, cooling, cleaning, and redecorating can cause the release and spread of indoor pollutants at home. Studies have shown that the air in our homes can be even more polluted than outdoor air.

Many Americans spend up to 90 percent of their time indoors, often at home. Therefore, breathing clean indoor air can have an important impact on health. People who are inside a great deal may be at greater risk of developing health problems, or having problems made worse by indoor air pollutants. These people include infants, young children the elderly and those with chronic illnesses.

What are Biological Pollutants?

Biological pollutants are or were living organisms. They promote poor indoor air quality and may be a major cause of days lost from work or school, and of doctor and hospital visits. Some can even damage surfaces inside and outside your house. Biological pollutants can travel through the air and are often invisible.

Some common indoor biological pollutants are:

  • Animal Dander (minute scales from hair, feathers, or skin)
  • Dust Mite and Cockroach parts
  • Infectious agents (bacteria or viruses)
  • Pollen

Some of these substances are in every home. It is impossible to get rid of them all. Even a spotless home may permit the growth of biological pollutants. Two conditions are essential to support biological growth nutrients and moisture. These conditions can be found in many locations, such as bathrooms, damp or flooded basements, wet appliances (such as humidifiers or air conditioners), and even some carpets and furniture.

Modern materials and construction techniques may reduce the amount of outside air brought into buildings which may result in high moisture levels inside. Using humidifiers, unvented heaters, and air conditioners in our homes has increased the chances of moisture forming on interior surfaces. This encourages the growth of certain biological pollutants.

The Scope of the Problem

Most information about sources and health effects of biological pollutants is based on studies of large office buildings and two surveys of homes in northern U.S. and Canada. These surveys show that 30% to 50% of all structures have damp conditions which may encourage the growth and buildup of biological pollutants. This percentage is likely to be higher in warm, moist climates.

Some diseases or illnesses have been linked with biological pollutants in the indoor environment. However, many of them also have causes unrelated to the indoor environment. Therefore, we do nut know how many health problems relate only to poor indoor air.

Health Effects of Biological Pollutants

All of us are exposed to biological pollutants. However, the effects on our health depend upon the type and amount of biological pollution and the inpidual person. Some people do not experience health reactions from certain biological pollutants, while others may experience one or more of the following reactions:

  • Allergic
  • Infectious
  • Toxic

Except for the spread of infections indoors, ALLERGIC REACTIONS may be the most common health problem with indoor air quality in homes. They are often connected with animal dander (mostly from cats and dogs), with house dust mites (microscopic animals living in household dust), and with pollen. Allergic reactions can range from mildly uncomfortable to life-threatening, as in a severe asthma attack. Some common signs and symptoms are:

  • Watery eyes
  • Runny nose and sneezing
  • Nasal congestion
  • Itching
  • Coughing
  • Wheezing and difficulty breathing
  • Headache
  • Fatigue

Health experts are especially concerned about people with asthma These people have very sensitive airways that can react to various irritants, making breathing difficult. The number of people who have asthma has greatly increased in recent years. The number of people with asthma has gone up by 59 percent since 1970, to a total of 9.6 million people. Asthma in children under 15 years of age has increased 41 percent in the same period, to a total of 2.6 million children. The number of deaths from asthma is up by 68 percent since 1979, to a total of almost 4,400 deaths per year.

Talking to Your Doctor

Are you concerned about the effects on your health that may be related to biological pollutants in your home? Before you discuss your concerns with your doctor, you should know the answers to the following questions. This information can help the doctor determine whether your health problems may be related to biological pollution.

  • Does anyone in the family have frequent headaches, fevers, itchy watery eyes, a stuffy nose, dry throat, or a cough? Does anyone complain of feeling tired or dizzy all the time? Is anyone wheezing or having difficulties breathing on a regular basis?
  • Did these symptoms appear after you moved to a new or different home?
  • Do the symptoms disappear when you go to school or the office or go away on a trip, and return when you come back?
  • Have you recently remodeled your home or done any energy conservation work, such as installing insulation, storm windows, or weather stripping? Did your symptoms occur during or after these activities?
  • Does your home feel humid? Can you see moisture on the windows or on other surfaces, such as walls and ceilings?
  • What is the usual temperature in your home? Is it very hot or cold?
  • Have you recently had water damage?
  • Is your basement wet or damp?
  • Is there any obvious mold or mildew?
  • Does any part of your home have a musty or moldy odor?
  • Is the air stale?
  • Do you have pets?
  • Do your house plants show signs of mold?
  • Do you have air conditioners or humidifiers that have not been properly cleaned?
  • Does your home have cockroaches or rodents?

INFECTIOUS DISEASES caused by bacteria and viruses, such as flu, measles, chicken pox, and tuberculosis, may be spread indoors. Most infectious diseases pass from person to person through physical contact. Crowded conditions with poor air circulation can promote this spread. Some bacteria and viruses thrive in buildings and circulate through indoor ventilation systems. For example, the bacterium causing Legionnaire’s disease, a serious and sometimes lethal infection, and Pontiac Fever, a flu-like illness, have circulated in some large buildings.

TOXIC REACTIONS are the least studied and understood health problem caused by some biological air pollutants in the home. Toxins can damage a variety of organs and tissues in the body, including the liver, the central nervous system, the digestive tract, and the immune system.

Coping with the Problem

Checking Your Home

There is no simple and cheap way to sample the air in your home to determine the level of all biological pollutants. Experts suggest that sampling for biological pollutants is not a useful problem-solving tool. Even if you had your home tested, it is almost impossible to know which biological pollutant(s) cause various symptoms or health problems. The amount of most biological substances required to cause disease is unknown and varies from one person to the next.

Does this make the problem sound hopeless? On the contrary, you can take several simple, practical actions to help remove sources of biological pollutants, to help get rid of pollutants, and to prevent their return.

Self-Inspection: A Walk Through Your Home

Begin by touring your household. Follow your nose, and use your eyes. Two major factors help create conditions for biological pollutants to grow nutrients and constant moisture with poor air circulation.

Dust and construction materials, such as wood, wallboard, and insulation, contain nutrients that allow biological pollutants to grow. Firewood also is a source of moisture, fungi, and bugs.

Appliances such as humidifiers, kerosene and gas heaters, and gas stoves add moisture to the air.

A musty odor, moisture on hard surfaces, or even water stains, may be caused by:

  • Air-conditioning units
  • Basements, attics, and crawlspaces
  • Bathrooms
  • Carpets
  • Heating and air-conditioning ducts
  • Humidifiers and dehumidifiers
  • Refrigerator drip pans

What You Can Do about Biological Pollutants

Before you give away the family pet or move, there are less drastic steps that can be taken to reduce potential problems. Properly cleaning and maintaining your home can help reduce the problem and may avoid interrupting your normal routine. People who have health problems such as asthma, or are allergic, may need to do this and more. Discuss this with your doctor.

Moisture Control

Water in your home can come from many sources. Water can enter your home by leaking or by seeping through basement floors. Showers or even cooking can add moisture to the air in your home. The amount of moisture that the air in your home can hold depends on the temperature of the air. As the temperature goes down, the air is able to hold less moisture. This is why, in cold weather, moisture condenses on cold surfaces (for example, drops of water form on the inside of a window). This moisture can encourage biological pollutants to grow.

There are many ways to control moisture in your home:

  • Fix leaks and seepage. If water is entering the house from the outside, your options range from simple landscaping to extensive excavation and waterproofing. (The ground should slope away from the house). Water in the basement can result from the lack of gutters or a water flow toward the house. Water leaks in pipes or around tubs and sinks can provide a place for biological pollutants to grow.
    Put a plastic cover over dirt crawlspaces to prevent moisture from coming in from the ground. Be sure crawlspaces are well-ventilated.
  • Use exhaust fans in bathrooms and kitchens to remove moisture to the outside (not into the attic) Vent your clothes dryer to the outside.
  • Turn off certain appliances (such as humidifiers or kerosene heaters) if you notice moisture on windows and other surfaces.
  • Use dehumidifiers and air conditioners, especially in hot, humid climates, to reduce moisture in the air, but be sure that the appliances themselves don’t become sources of biological pollutants.
  • Raise the temperature of cold surfaces where moisture condenses. Use insulation or storm windows. (A storm window installed on the inside works better than one installed on the outside ) Open doors between rooms (especially doors to closets which may be colder than the rooms) to increase circulation. Circulation carries heat to the cold surfaces Increase air circulation by using fans and by moving furniture from wall corners to promote air and heat circulation. Be sure that your house has a source of fresh air and can expel excessive moisture from the home.
  • Pay special attention to carpet on concrete floors. Carpet can absorb moisture and serve as a place for biological pollutants to grow. Use area rugs which can be taken up and washed often In certain climates, if carpet is to be installed over a concrete floor, it maybe necessary to use a vapor barrier (plastic sheeting) over the concrete and cover that with sub-flooring (insulation covered with plywood) to prevent a moisture problem.
  • Moisture problems and their solutions differ from one climate to another. The Northeast is cold and wet, the Southwest is hot and dry, the South is hot and wet, and the Western Mountain states are cold and dry. All of these regions can have moisture problems. For example, evaporative coolers used in the Southwest can encourage the growth of biological pollutants. In other hot regions, the use of air conditioners which cool the air too quickly may prevent the air conditioners from running long enough to remove excess moisture from the air. The types of construction and weatherization for the different climates can lead to different problems and solutions.

Where Biological Pollutants may be Found in the Home






1. Dirty air conditioners

2. Dirty humidifiers and/or dehumidifiers

3. Bathroom without vents or windows

4. Kitchen without vents or windows

5. Dirty refrigerator drip pans

6. Laundry room with unvented dryer

7. Unventilated attic






8. Carpet on damp basement floor

9. Bedding

10. Closet on outside wall

11. Dirty heating/air conditioning system

12. Dogs or cats

13. Water damage (around windows, the roof or the basement)

Maintain and Clean all Appliances that Come in Contact with Water

  • Have major appliances, such as furnaces, heat pumps and central air conditioners, inspected and cleaned regularly by a professional, especially before seasonal use. Change filters on heating and cooling systems according to manufacturer’s directions. (In general, change filters monthly during use.) When first turning on the heating or air conditioning at the start of the season, consider leaving your home until it airs out.
  • Have window or wall air-conditioning units cleaned and serviced regularly by a professional, especially before the cooling season. Air conditioners can help reduce the entry of allergy-causing pollen. But they may also become a source of biological pollutants if not properly maintained. Clean the coils and rinse the drain pans according to manufacturer’s instructions, so water can-not collect in pools.
  • Have furnace-attached humidifiers cleaned and serviced regularly by a professional, especially before the heating season.
  • Follow manufacturer’s instructions when using any type of humidifier Experts differ on the benefits of using humidifiers. If you do use a portable humidifier (approximately 1 to 2 gallon tanks), be sure to empty its tank every day and refill with distilled or demineralized water, or even fresh tap water if the other types of water are unavailable For larger portable humidifiers, change the water as recommended by the manufacturer. Unplug the appliance before cleaning. Every third day, clean all surfaces coming in contact with water with a 3% solution of hydrogen peroxide, using a brush to loosen deposits Some manufacturers recommend using diluted household bleach for cleaning and maintenance, generally in a solution of one-half cup bleach to one gallon water When any household chemical, rinse well to remove all traces of chemical before refilling humidifier.
  • Empty dehumidifiers daily and clean often. If possible, have the appliance drip directly into a drain. Follow manufacturer’s instructions for cleaning and maintenance. Always disconnect the appliance before cleaning.
  • Clean refrigerator drip pans regularly according to manufacturer’s instructions. If refrigerator and freezer doors don’t seal properly, moisture may build up and mold can grow. Remove any mold on door gaskets and replace faulty gaskets.

Clean Surfaces

  • Clean moist surfaces, such as showers and kitchen counters.
  • Remove mold from walls, ceilings, floors, and paneling. Do not simply cover mold with paint, stain, varnish, or a moisture-proof sealer, as it may resurface.
  • Replace moldy shower curtains, or remove them and scrub well with a household cleaner and rinse before rehanging them.

Dust Control

Controlling dust is very important for people who are allergic to animal dander and mites. You cannot see mites, but you can either remove their favorite breeding grounds or keep these areas dry and clean. Dust mites can thrive in sofas, stuffed chairs, carpets, and bedding. Open shelves, fabric wallpaper, knickknacks, and venetian blinds are also sources of dust mites. Dust mites live deep in the carpet and are not removed by vacuuming. Many doctors suggest that their mite-allergic patients use washable area rugs rather than wall-to-wall carpet.

  • Always wash bedding in hot water (at least 130° F) to kill dust mites. Cold water won’t do the job. Launder bedding at least every 7 to 10 days.
  • Use synthetic or foam rubber mattress pads and pillows, and plastic mattress covers if you are allergic Do not use fuzzy wool blankets, feather or wool-stuffed comforters, and feather pillows.
  • Clean rooms and closets well, dust and vacuum often to remove surface dust. Vacuuming and other cleaning may not remove all animal dander, dust mite material, and other biological pollutants. Some particles are so small they can pass through vacuum bags and remain in the air If you are allergic to dust, wear a mask when vacuuming or dusting. People who are highly allergy-prone should not perform these tasks. They may even need to leave the house when someone else is cleaning.

Before You Move

Protect yourself by inspecting your potential new home. If you identify problems, have the landlord or seller correct them before you move in, or even consider moving elsewhere.

  • Have professionals check the heating and cooling system, including humidifiers and vents. Have duct lining and insulation checked for growth.
  • Check for exhaust fans in bathrooms and kitchens If there are no vents, do the kitchen and bathrooms have at least one window a piece? Does the cook top have a hood vented outside? Does the clothes dryer vent outside? Are all vents to the outside of the building, not in attics or crawlspaces?
  • Look for obvious mold growth throughout the house, including attics, basements, and crawlspaces and around the foundation. See if there are many plants close to the house, particularly if they are damp and rotting. They are a potential source of biological pollutants. Downspouts from roof gutters should route water away from the building.
  • Look for stains on the walls, floor or carpet (including any carpet over concrete floors) as evidence of previous flooding or moisture problems. Is there moisture on windows and surfaces? Are there signs of leaks or seepage in the basement?
  • Look for rotted building materials which may suggest moisture or water damage.
  • If you or anyone else in the family has a pet allergy, ask if any pets have lived in the home.
  • Examine the design of the building. Remember that in cold climates, overhanging areas, rooms over unheated garages, and closets on outside walls may be prone to problems with biological pollutants.
  • Look for signs of cockroaches.


Carefully read instructions for use and any cautionary labeling on cleaning products before beginning cleaning procedures.

  • Do not mix any chemical products. Especially, never mix cleaners containing bleach with any product (such as ammonia) which does not have instructions for such mixing. When chemicals are combined, a dangerous gas can sometimes be formed.
  • Household chemicals may cause burning or irritation to skin and eyes.
  • Household chemicals may be harmful if swallowed, or inhaled.
  • Avoid contact with skin, eyes, mucous membranes and clothing.
  • Avoid breathing vapor. Open all windows and doors and use an exhaust fan that sends the air outside.
  • Keep household chemicals out of reach of children.
  • Rinse treated surface areas well to remove all traces of chemicals.
  • Correcting Water Damage

What if damage is already done? Follow these guidelines for correcting water damage:

  • Throw out mattresses, wicker furniture, straw baskets and the like that have been water damaged or contain mold. These cannot be recovered.
  • Discard any water-damaged furnishings such as carpets, drapes, stuffed toys, upholstered furniture and ceiling tales, unless they can be recovered by steam cleaning or hot water washing and thorough drying.
  • Remove and replace wet insulation to prevent conditions where biological pollutants can grow.

 Preventing Sinusitis


You’re coughing and sneezing and tired and achy. You think that you might be getting a cold. Later, when the medicines you’ve been taking to relieve the symptoms of the common cold are not working and you’ve now got a terrible headache, you finally drag yourself to the doctor. After listening to your history of symptoms and perhaps doing a sinus X-ray, the doctor says you have sinusitis.

Sinusitis simply means inflammation of the sinuses, but this gives little indication of the misery and pain this condition can cause. Chronic sinusitis, sinusitis that recurs frequently, affects an estimated 32 million people in the United States. Americans spend millions of dollars each year for medications that promise relief from their sinus symptoms.

Sinuses are hollow air spaces, of which there are many in the human body. When people say, “I’m having a sinus attack,” they usually are referring to symptoms in one or more of four pairs of cavities, or spaces, known as paranasal sinuses. These cavities, located within the skull or bones of the head surrounding the nose, include the frontal sinuses over the eyes in the brow area, the maxillary sinuses inside each cheekbone, the ethmoids just behind the bridge of the nose and between the eyes, and behind them, the sphenoids in the upper region of the nose and behind the eyes.

Each sinus has an opening into the nose for the free exchange of air and mucus, and each is joined with the nasal passages by a continuous mucous membrane lining. Therefore, anything that causes a swelling in the nose-an infection or an allergic reaction-also can affect the sinuses. Air trapped within an obstructed sinus, along with pus or other secretions, may cause pressure on the sinus wall. The result is the sometimes intense pain of a sinus attack. Similarly, when air is prevented from entering a paranasal sinus by a swollen membrane at the opening, a vacuum can be created that also causes pain.


Sinusitis has its own localized pain signals, depending upon the particular sinus affected. Headache upon awakening in the morning is characteristic of sinus involvement. Pain when the forehead over the frontal sinuses is touched may indicate inflammation of the frontal sinuses. Infection in the maxillary sinuses can cause the upper jaw and teeth to ache and the cheeks to become tender to the touch. Since the ethmoid sinuses are near the tear ducts in the corner of the eyes, inflammation of these cavities often causes swelling of the eyelids and tissues around the eyes and pain between the eyes. Ethmoid inflammation also can cause tenderness when the sides of the nose are touched, a loss of smell, and a stuffy nose. Although the sphenoid sinuses are less frequently affected, infection in this area can cause earaches, neck pain, and deep aching at the top of the head.

Other symptoms of sinusitis can include fever, weakness, tiredness, a cough that may be more severe at night, and runny nose or nasal congestion. In addition, drainage of mucus from the sphenoids down the back of the throat (postnasal drip) can cause a sore throat and can irritate the membranes lining the larynx (upper windpipe).


Most cases of acute sinusitis are caused by viruses and will clear up without treatment within two weeks. Viruses can enter the body through the nasal passages and set off a chain reaction resulting in sinusitis. For example, the nose reacts to an invasion by viruses that cause infections such as the common cold, flu, or measles by producing mucus and sending white blood cells to the lining of the nose, which congest and swell the nasal passages. When this swelling involves the adjacent mucous membranes of the sinuses, air and mucus are trapped behind the narrowed openings of the sinuses. If the sinus openings become too narrow to permit drainage of the mucus, then bacteria, which normally are present in the respiratory tract, begin to multiply. Most apparently healthy people harbor bacteria, such as Streptococcus pneumoniae and Haemophilus influenzae, in their upper respiratory tracts with no ill effects until the body’s defenses are weakened or drainage from the sinuses is blocked by a cold or other viral infection. The bacteria that may have been living harmlessly in the nose, throat, or sinus area can multiply and cause an acute sinus infection.

Medicines, too, can set off a nasal reaction with accompanying sinusitis. For example, intolerance to aspirin and other related non-steroidal anti-inflammatory medications, such as ibuprofen, can be associated with sinusitis in patients with asthma or nasal polyps (small growths on the mucous membrane lining of the sinuses).

Sometimes, fungal infections can cause acute sinusitis. Although these organisms are abundant in the environment, they usually are harmless to healthy people, indicating that the human body has a natural resistance to them. Fungi, such as Aspergillus and Curvularia, can cause serious illness, in people whose immune systems are not functioning properly. Some people with fungal sinusitis have an allergic-type reaction to the fungi.

Chronic inflammation of the nasal passages (rhinitis) also can lead to sinusitis. Allergic rhinitis or hay fever (discussed below) is the mostcommon cause of chronic sinusitis and is a frequent cause of acute sinusitis. Vasomotor rhinitis, caused by humidity, cold air, alcohol, perfumes, and other environmental conditions, also can result in a sinus infection.

Chronic Sinusitis

Chronic sinusitis refers to inflammation of the sinuses that continues for weeks, months, or even years.

As noted above, allergies are the most common cause of chronic sinusitis. Inhalation of airborne allergens (foreign substances that provoke an allergic reaction), such as dust, mold, and pollen, often set off allergic reactions (allergic rhinitis) that, in turn, may contribute to sinusitis. People who are allergic to fungi can develop a condition called “allergic fungal sinusitis.” As body cells react against these inhaled substances, they release chemical compounds, such as histamine, at the mucosal surface. These chemicals then cause the nasal passages to swell and block drainage from the sinuses, resulting in sinusitis.

Damp weather, especially in northern temperate climates, or pollutants in the air and in buildings also can affect people subject to chronic sinusitis.

Chronic sinusitis can be caused by structural abnormalities of the nose, such as a deviated septum (the bony partition separating the two nasal passages), or by small growths called nasal polyps, both of which can trap mucus in the sinuses.


Although a stuffy nose can occur in other conditions, like the common cold, many people confuse simple nasal congestion with sinusitis. A cold, however, usually lasts about seven days and disappears without treatment. Acute sinusitis often lasts longer than a week. A doctor can diagnose sinusitis by medical history, physical examination, X-rays, and if necessary, MRIs or CT scans (magnetic resonance imaging and computed tomography).


After diagnosing sinusitis and identifying a possible cause, a doctor can prescribe a course of treatment that will clear up the source of the inflammation and relieve the symptoms. Sinusitis is treated by re-establishing drainage of the nasal passages, controlling or eliminating the source of the inflammation, and relieving the pain. Doctors generally recommend decongestants to reduce the congestion, antibiotics to control a bacterial infection, if present, and pain relievers to reduce the pain.

Over-the-counter and prescription decongestant nose drops and sprays, however, should not be used for more than a few days. When used for longer periods, these drugs can lead to even more congestion and swelling of the nasal passages.

If symptoms do not improve within 10 to 14 days, the cause of sinusitis is likely to be bacterial. Most patients with sinusitis that is caused by bacteria can be treated successfully with antibiotics used along with a nasal or oral decongestant. A narrow-spectrum antibiotic — one that fights the most common bacteria — is the initial treatment recommended.

For many years, the combination of allergic disease and infectious sinusitis has been considered the most difficult form of sinus disease to treat. The patient with uncontrolled nasal allergies frequently experiences a lot of congestion, swelling, excess secretions, and discomfort in the sinus areas. Therefore, the patient should work with a doctor who understands the diagnosis and treatment of allergic diseases to pinpoint the cause of the allergies and follow an allergy care program to help alleviate sinusitis.

Doctors often prescribe steroid nasal sprays, along with other treatments, to reduce the congestion, swelling, and inflammation of sinusitis. Because steroid nasal sprays have no serious side effects, they can be used for long-term treatment. In some people, however, they irritate the nasal passages.

For patients with severe chronic sinusitis, a doctor may prescribe oral steroids, such as prednisone. Because oral steroids can have significant side effects, they are prescribed only when other medications have not been effective.

Although sinus infection cannot be cured by home remedies, people can use them to lessen their discomfort. Inhaling steam from a vaporizer or a hot cup of water can soothe inflamed sinus cavities. Another treatment is saline nasal spray, which can be purchased in a pharmacy. A hot water bottle; hot, wet compresses; or an electric heating pad applied over the inflamed area also can be comforting.

In treating patients with severe sinusitis, a physician may use special procedures. One technique requires the patient to lie on his back with his head over the edge of the examining table. A decongestant fluid is placed in the nose, and air is suctioned out of the nose so that the decongestant fluid can shrink the sinus membranes sufficiently to permit drainage. Or, a thin tube can be inserted into the sinuses for washing out entrapped pus and mucus.

Sometimes, however, surgery is the only alternative for preventing chronic sinusitis. In children, problems often are eliminated by removal of adenoids obstructing nasal-sinus passages. Adults who have had allergic and infectious conditions over the years sometimes develop polyps that interfere with proper drainage. Removal of these polyps and/or repair of a deviated septum to ensure an open airway often provides considerable relief from sinus symptoms. The most common surgery done today is functional endoscopic sinus surgery, in which the natural openings from the sinuses are enlarged to allow drainage.


Although people cannot prevent all sinus disorders-any more than they can avoid all colds or bacterial infections-they can take certain measures to reduce the number and severity of the attacks and possibly prevent sinusitis from becoming chronic. Appropriate amounts of rest, a well-balanced diet, and exercise can help the body function at its most efficient level and maintain a general resistance to infections. Eliminating environmental factors, such as climate and pollutants, is not always possible, but they can often be controlled.

Many people with sinusitis find partial relief from their symptoms when humidifiers are installed in their homes, particularly if room air is heated by a dry forced-air system. Air conditioners help to provide an even temperature, and electrostatic filters attached to heating and air conditioning equipment are helpful in removing allergens from the air.

A person susceptible to sinus disorders, particularly one who also is allergic, should avoid cigarette smoke and other air pollutants.

Inflammation in the nose caused by allergies predisposes a patient to a strong reaction to all irritants. Drinking alcohol also causes the nasal-sinus membranes to swell.

Sinusitis-prone persons may be uncomfortable in swimming pools treated with chlorine, since it irritates the lining of the nose and sinuses. pers often experience congestion with resulting infection when water is forced into the sinuses from the nasal passages.

Air travel, too, poses a problem for the inpidual suffering from acute or chronic sinusitis. A bubble of air trapped within the body expands as air pressure in a plane is reduced. This expansion causes pressure on surrounding tissues and can result in a blockage of the sinuses or the eustachian tubes in the ears. The result may be discomfort in the sinus or middle ear during the plane’s ascent or descent. Doctors recommend using decongestant nose drops or inhalers before the flight to avoid this difficulty.

People who suspect that their sinus inflammation may be related to dust, mold, pollen, or food-or any of the hundreds of allergens that can trigger a respiratory reaction-should consult a doctor. Various tests can determine the cause of the allergy and also help the doctor recommend steps to reduce or limit allergy symptoms.

NIAID, a component of the National Institutes of Health, supports research on AIDS, tuberculosis and other infectious diseases as well as allergies and immunology.

Prepared by:


Office of Communications and Public Liaison
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892




Public Health Service:

U.S. Department of Health and Human Services
June 1998

 Asthma Causes and Triggers

Clear Your Home of Asthma Triggers

Your children will breathe easier

Act now against asthma at home. Asthma is a serious lung disease.

  • During an asthma attack, the airways get narrow, making it difficult to breathe.
  • Symptoms of asthma include wheezing, shortness of breath, and coughing.
  • Asthma can even cause death.
If you have asthma or a child with asthma, you are not alone.

  • About 17 million Americans have asthma.
  • Asthma is the leading cause of long-term illness in children.
The air that children breathe can make a difference.

  • Asthma may be triggered by allergens and irritants that are common in homes.
  • Help your child breathe easier: consult a doctor and reduce asthma triggers in your home.

Clear Your Home of Asthma Triggers

Below are five common asthma triggers found in homes and what you can do to reduce you and your child’s exposure to them. Not all of the asthma triggers listed here affect every person with asthma. Not all asthma triggers are listed here. See your doctor or health care provider for more information.

Secondhand Smoke

Asthma can be triggered by the smoke from the burning end of a cigarette, pipe, or cigar and the smoke breathed out by a smoker.

  • Choose not to smoke in your home or car and do not allow others to do so either.
Dust Mites

Dust mites are too small to be seen but are found in every home.

Dust mites live in mattresses, pillows, carpets, fabric-covered furniture, bedcovers, clothes, and stuffed toys.

  • Wash sheets and blankets once a week in hot water.
  • Choose washable stuffed toys, wash them often in hot water, and dry thoroughly. Keep stuffed toys off beds.
  • Cover mattresses and pillows in dust-proof (allergen-impermeable) zippered covers.

Your pet’s skin flakes, urine, and saliva can be asthma triggers.

  • Consider keeping pets outdoors or even finding a new home for your pets, if necessary.
  • Keep pets out of the bedroom and other sleeping areas at all times, and keep the door closed.
  • Keep pets away from fabric-covered furniture, carpets, and stuffed toys.

Molds grow on damp materials. The key to mold control is moisture control.

If mold is a problem in your home, clean up the mold and get rid of excess water or moisture.

Lowering the moisture also helps reduce other triggers, such as dust mites and cockroaches.

  • Wash mold off hard surfaces and dry completely. Absorbent materials, such as ceiling tiles and carpet, with mold may need to be replaced.
  • Fix leaky plumbing or other sources of water.
  • Keep drip pans in your air conditioner, refrigerator, and dehumidifier clean and dry.
  • Use exhaust fans or open windows in kitchens and bathrooms when showering, cooking, or using the dishwasher.
  • Vent clothes dryers to the outside.
  • Maintain low indoor humidity, ideally between 30-50% relative humidity. Humidity levels can be measured by hygrometers which are available at local hardware stores.

Droppings or body parts of pests such as cockroaches or rodents can be asthma triggers.

  • Do not leave food or garbage out.
  • Store food in airtight containers.
  • Clean all food crumbs or spilled liquids right away.
  • Try using poison baits, boric acid (for cockroaches), or traps first before using pesticidal sprays.
  • If sprays are used:
    • Limit the spray to infested area.
    • Carefully follow instructions on the label.
    • Make sure there is plenty of fresh air when you spray, and keep the person with asthma out of the room.
Also… House dust may contain asthma triggers. Remove dust often with a damp cloth, and vacuum carpet and fabric-covered furniture to reduce dust build-up. Allergic people should leave the area being vacuumed. Using vacuums with high efficiency filters or central vacuums may be helpful.

When your local weather forecast announces an ozone action day, stay indoors as much as possible.

For more information:

You can request information from EPA’s:

Indoor Air Quality Information Clearinghouse (IAQ INFO)
P.O. Box 37133
Washington, DC 20013-7133
(800) 438-4318, or
(703) 356-4020 (local)
(703) 356-5386 (fax)

Other related sites:

National Academy of Sciences Report – “Clearing the Air: Asthma and Indoor Air Exposures”

Two years ago, the Environmental Protection Agency (EPA) asked the National Academy of Sciences (NAS) to undertake an assessment of the role of indoor air quality in the growing asthma problem. EPA asked NAS to characterize the state of the science on health impacts and prevention strategies, and to provide recommendations on needed research. In response to this request, the National Academy of Sciences Institute of Medicine has issued a report, Clearing the Air: Asthma and Indoor Air Exposures, on the role of indoor environmental pollutants in the development and exacerbation of asthma. The report affirms the Administrator’s asthma initiative to educate the public about the ways they can help control asthma by managing indoor air quality. The report concludes that exposure to indoor pollutants is an important contributor to the asthma problem in this nation. Asthma sufferers should consult with their doctor about reducing their exposure to secondhand smoke, dust mites, pet dander, molds, and cockroaches.

 The 10 Most Dangerous Toxins in Your Home

The 10 Most Dangerous Toxins in Your Household

By Claude Morgan

It’s official: Staying home is hazardous to your health. Toxins found in the home injured 789,000 Americans between 1992 and 1995, and new research suggests that this figure is underestimated.

“Toxins in U.S. homes now account for 90 percent of all reported poisonings each year,” says Rose Ann Soloway, administrator of the American Association of Poison Control Centers. That’s an epidemic of hazardous living by any standard. And while these figures include everything from non-fatal aspirin overdoses to the deadly consumption of drain cleaners, they fail to include long-term exposure to toxins like lead and asbestos.

To address the climbing domestic injury rates associated with household toxins, Congress and the Centers for Disease Control (CDC) in 1992 created the Unintentional Injury Center to focus on the health dangers of consumer goods and modern home living. Other federal agencies are following suit. The Environmental Protection Agency (EPA) now has branches which deal with home indoor air quality, lead exposure and ubiquitous low-level toxicity, and the Department of Housing and Urban Development publishes a pollution look-out list for first-time homebuyers.

The short list of toxins under your roof may surprise you:

* Formaldehyde offgasses (evaporates) from cushions, particleboard and adhesives used to manufacture most inexpensive wood-based products. Carpets and carpet cushions may also offgas formaldehyde, causing eye and upper respiratory irritation. According to the EPA, formaldehyde may even cause cancer;

* Radon is the second-leading cause of lung cancer in the U.S., warns the Surgeon General. Radon is a natural radioactive gas which can seep into homes through cracks in the basement, the surrounding foundation, and in well water. It enters the body quietly through the airway;

* Lead keeps epidemiologists returning to the drawing board, says Soloway, “mostly because we know more now about the adverse effects of low-level exposure.” Levels once thought to be acceptable are now known contributors to learning disabilities and behavioral problems. Lead is found in paint in older houses, old plumbing, and soil near highways and busy roads. It causes neurological and kidney damage, high blood pressure, disrupted blood cell production, and reproductive problems;

* Carbon monoxide will kill an estimated 660 Americans this year. Don’t look for exhaust fumes in the attached garage; the biggest culprit is the unserviced furnace burning propane, butane or oil;

* Arsenic is still laced in many household pesticides and is increasingly used as a wood preservative. Low levels of inorganic arsenic “may increase lung cancer risk,” according to the CDC. The Department of Health and Human Services agrees, adding arsenic compounds to the list of known carcinogens;

* Vinyl chloride is the source of “new car smell”: The plastic interior of a new car offgasses this known carcinogen. Water sitting in PVC pipes overnight may be steeping into a toxic tea. Very large exposures can lead to “vinyl chloride disease,” which causes severe liver damage and ballooning of the fingertips;

* Hydrofluoric acid “can cause intense pain and damage to tissues and bone if the recommended gloves happen to have holes in them,” says Soloway. This highly corrosive substance is the active ingredient in many household rust removers;

But even the most liberal list of known toxins pales next to the order of volatile organic compounds (VOCs). VOCs comprise hundreds of natural and man-made, carbon-based agents. They react quickly with other carbon-based compounds, and evaporate easily, making them ideal solvents. VOCs can be found in disinfectants and pesticides too.

* Solvents: Benzene and methyl ethyl ketone traverse cell walls unchecked by normal cell defenses. Both are known carcinogens. Cousins toluene, xylene, 1,1,1-trichloroethane (TCA) and trichloroethylene (TCE) make up the lion’s share of the solvent market;

* Disinfectants: Phenols, which include biphenyl, phenolics and the preservative pentachloraphenol, are found in disinfectants, antiseptics, perfumes, mouthwashes, glues and air fresheners;

* Pesticides: Chlordane, aldrin, dieldrin, though all banned for nearly two decades, continue to show up airborne in older houses.

Don’t be a statistical figure on the CDC’s tracking list: Be aware of what substances, from pesticides to cleaners, pose real threats in your household. Maintain ingredient awareness. Many poisonings still occur because of product combinations, like the ammonia-chlorine bleach reaction, which produces the deadly respiratory irritant chloramine (a problem labeling practices have not addressed). Replace toxic agents with non-toxic alternatives. Above all, educate your household to reduce risk and exposure.

For practical ideas on reducing risk, consult the following books: Living Healthy in a Toxic World by David Steinman and R. Michael Wisner (Berkley, 1996); Toxins A-Z: A Guide to Everyday Pollution Hazards by John Harte, Cheryl Holdren, Richard Schneider, and Christine Shirley (University of California, 1991); Home Safe Home: Protecting Yourself and Your Family from Everyday Toxics and Harmful Household Products by Debra L. Dadd (Putnam, 1997).

For more information, contact the Unintentional Injury Center, (770)488-4652.

(Claude Morgan is a freelance writer based in Maine who contributes to E, the Environmental Magazine.)

Copyright 1997, The Los Angeles Times Syndicate, All Rights Reserved

 Residential Air Cleaning Devices

Residential Air Cleaning Devices

A Summary of Available Information

Office of Air and Radiation (OAR)
Washington, DC 20460
EPA 400/1-90-002, February 1990

Disclaimer: This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of any trade names or commercial products does not constitute endorsement or recommendation for use.


Indoor air pollutants are unwanted, sometimes harmful materials in the air. They range from dusts to chemicals to radon. Air cleaners are devices that attempt to remove such pollutants from the indoor air you breathe.

The typical furnace filter installed in the ductwork of most home heating and/or air-conditioning systems is a simple air cleaner. This basic filtering system may be upgraded by using another filter to trap additional pollutants or by adding additional air-cleaning devices. An alternative to upgrading the induct air cleaning system is using inpidual room, portable air cleaners. Air cleaners generally rely on filtration, or the attraction of charged particles to the air cleaning device itself or to surfaces within the home, for the removal of pollutants. The use of “air cleaning” to remove pollutants from the air in residences is in its infancy; this publication presents the current state of knowledge.

This publication describes the types of air cleaners available to the consumer, provides available information on their general effectiveness in removing indoor air pollutants, discusses some factors to consider in deciding whether to use an air-cleaning unit, and describes existing guidelines that can be used to compare units. It does not discuss the effectiveness of air-cleaning systems installed in the central heating, ventilating, and air-conditioning (HVAC) systems of large buildings, such as apartment, office, or public buildings, nor does it evaluate specific products.

Because many factors need to be considered in determining whether use of an air cleaner is appropriate in a particular setting, the decision whether or not to use an air cleaner is left to the inpidual. EPA has not taken a position either for or against the use of these devices in the home.

What Pollutants are of Concern in Indoor Air?

For the purposes of discussion, we will pide the pollutants into three groups: particles, gaseous pollutants, and radon and its progeny.

Particles are very small solid or liquid substances that are light enough to float suspended in air (e.g., mists, dust, or pollen). They are composed of perse materials including inorganic and organic compounds and dormant and living organisms. Of primary concern from a health standpoint are: 1) small, invisible respirable-size particles, with a higher probability of penetrating deep into the lungs, where they may stay a long time and may cause acute or chronic effects, and 2) larger particles, such as some molds, pollen, animal dander, and house dust allergens, which do not penetrate as deeply, but may cause an allergic response.

Respirable-size particles include, but are not limited to, those from cigarette smoke; unvented combustion appliances such as gas stoves and kerosene heaters; viruses, bacteria, and some molds; and fragments of materials which, when whole, would be considered larger than respirable size particles. Health effects from exposure to respirable-size particles in the air depend on the types and concentrations of particles present, the frequency and duration of exposure, and inpidual sensitivity. Health effects can range from irritation of the eyes and/or respiratory tissues to more serious effects, such as cancer and decreased lung function. Biological particles, such as animal and insect allergens, viruses, bacteria, and molds, can cause allergic reactions, infectious diseases, and/or can produce toxic products which may be released into the air.

Gaseous pollutants include combustion gases and organic chemicals which are not associated with particles. Hundreds of different gaseous pollutants have been detected in indoor air.

Sources of combustion gases (such as carbon monoxide and nitrogen dioxide) include combustion appliances, cigarette smoking, and the infiltration of vehicle exhaust gases from attached garages or the outdoors.

Gaseous organic compounds may enter the air from sources such as cigarette smoking, building materials and furnishings, and the use of products such as paints, adhesives, dyes, solvents, caulks, cleaners, deodorizers, personal hygiene products, waxes, hobby and craft materials, and pesticides. In addition, organic compounds may originate outdoors or through cooking of foods and human, plant, and animal metabolic processes.

Health effects from exposure to gaseous pollutants in the air may vary widely depending on the types and concentrations of the chemicals present, the frequency and duration of exposure, and inpidual sensitivity. Adverse effects may include irritation of the eyes and/or respiratory tissues; allergic reactions; effects on the respiratory, liver, immune, cardiovascular, reproductive, and/or nervous system; and cancer.

Radon and its progeny are radioactive pollutants which originate from natural sources such as rock, soil, groundwater, natural gas, and mineral building materials. These pollutants have the potential to cause lung cancer in humans. The risk of lung cancer increases with the level in the air and the frequency and duration of exposure.

Radon itself is a gas which produces short-lived progeny in the form of particles, some of which become attached to larger particles. Radon progeny may deposit in the lungs and represent the main health hazard from the radon series.

How Does Air Cleaning Compare with other Strategies for Reducing Pollutant Concentrations in Indoor Air?

The three strategies (in order of effectiveness) for reducing pollutants in indoor air are source control, ventilation, and air cleaning.

Source control eliminates inpidual sources of pollutants or reduces their emissions, and is generally the most effective strategy. Some sources, like those that contain asbestos, can be sealed or enclosed; others, like combustion appliances, can be adjusted to decrease the amount of emissions. Unfortunately, not all pollutant sources can be identified and practically eliminated or reduced.

Ventilation brings outside air indoors. It can be achieved by opening windows and doors, by turning on local bathroom or kitchen exhaust fans, or, in some situations, by the use of mechanical ventilation systems, with or without heat recovery ventilators (air-to-air heat exchangers). However, there are practical limits to the extent ventilation can be used to reduce airborne pollutants. Costs for heating or cooling incoming air can be significant, and outdoor air itself may contain undesirable levels of contaminants.

Air cleaning may serve as an adjunct to source control and ventilation. However, the use of air cleaning devices alone cannot assure adequate air quality, particularly where significant sources are present and ventilation is inadequate.

What Types of Air Cleaners are Available?

Air cleaners are usually classified by the method employed to remove particles of various sizes from the air. There are three general types of air cleaners on the market: mechanical filters, electronic air cleaners, and ion generators. (Note: Because they may reduce some pollutants present in indoor air through condensation, absorption, and other mechanisms, devices such as air conditioners, humidifiers, and dehumidifiers may technically be considered air cleaners. However, this publication includes only those devices specifically designed and marketed as air cleaners.)

Mechanical filters may be installed in ducts in homes with central heating and/or air-conditioning or may be used in portable devices which contain a fan to force air through the filter. Mechanical filters used for air cleaning are of two major types.

Flat or panel filters generally consist either of a low packing density of coarse glass fibers, animal hair, vegetable fibers, or synthetic fibers often coated with a viscous substance (e.g., oil) to act as an adhesive for particulate material, or slit and expanded aluminum. (A flat filter in use in many homes is the typical furnace filter installed in central heating and/or air-conditioning systems.) Flat filters may efficiently collect large particles, but remove only a small percentage of respirable size particles.

Flat filters may also be made of “electret” media, consisting of a permanently-charged plastic film or fiber. Particles in the air are attracted to the charged material.

Pleated or extended surface filters generally attain greater efficiency for capture of respirable size particles than flat filters. Their greater surface area allows the use of smaller fibers and an increase in packing density of the filter without a large drop in air flow rate.

Electronic air cleaners use an electrical field to trap charged particles. Like mechanical filters, they may be installed in central heating and/or air-conditioning system ducts or may be portable units with fans. Electronic air cleaners are usually electrostatic precipitators or charged-media filters. In electrostatic precipitators, particles are collected on a series of flat plates. In charged-media filter devices, which are less common, the particles are collected on the fibers in a filter. In most electrostatic precipitators and some charged-media filters, the particles are deliberately ionized (charged) before the collection process, resulting in a higher collection efficiency.

Ion generators also use static charges to remove particles from indoor air. These devices come in portable units only. They act by charging the particles in a room, so they are attracted to walls, floors, table tops, draperies, occupants, etc. In some cases, these devices contain a collector to attract the charged particles back to the unit.

(Note: The latter two types of devices may produce ozone, either as a byproduct of use or intentionally. Concerns about ozone production are discussed in more depth later.)

Some newer systems on the market are referred to as “hybrid” devices. They contain two or more of the particle removal devices discussed above. For example, one or more types of mechanical filters may be combined with an electrostatic precipitator or an ion generator.

In addition to particle removal devices, air cleaners may also contain adsorbents and/or reactive materials to facilitate removal of gaseous materials from indoor air. Air cleaners which do not contain these types of materials will not remove gaseous pollutants. The potential effectiveness of air cleaners containing these materials in reducing levels of gaseous pollutants in indoor air is discussed later.

How Effective are Air Cleaners in Reducing Pollutant Concentrations in Indoor Air?

The effectiveness of air cleaners in removing pollutants from the air depends on both the efficiency of the device itself (e.g., the percentage of the pollutant removed as it goes through the device) and the amount of air handled by the device. For example, a filter may remove 99% of the pollutant in the air that passes through it, but if the air flow rate is only 10 cubic feet per minute (cfm), it will take a long time to process the air in a typical room of 1000 cubic feet.

Although there is no universally accepted method for comparing air-cleaning devices, several investigators of portable air-cleaning units have expressed their results as a “clean air delivery rate” or CADR. The CADR is the product of the unit efficiency and the air flow rate, and is a measure of the number of cfm of air it cleans of a specific material. For example, if an air cleaner has a CADR of 250 for smoke particles, it may reduce smoke particle levels to the same concentration as would be achieved by adding 250 cubic feet of clean (ventilation) air each minute.

The CADR can be used to compare removal rates between different devices and to estimate the removal rate of materials in larger or smaller rooms than those used in the tests.

Knowledge of both the CADR and the unit efficiency may be helpful in choosing a device for use in removing pollutants from a specific source. For example, a 45 percent efficient unit operating at a flow rate of 100 cfm has the same CADR as a 90 percent efficient unit operating at 50 cfm. Nevertheless, the 90 percent efficient unit placed near a specific source of pollutants would generally provide lower levels of the pollutant in the space away from the source than the 45 percent efficient unit.

In many cases, especially for in-duct systems and gaseous pollutant removal, only device efficiencies are reported, and the total effectiveness of the device would vary based on room size and air flow rate.

A summary of the results of studies on the effectiveness of air cleaners in removing particles, gaseous pollutants, and radon and its progeny follows.

Particle Removal

The performance of air cleaners in removing particles from indoor air depends not only on the air flow rate through the cleaner and the efficiency of its particle capture mechanism, but also on factors such as:

  • The mass of the particles entering the device.
  • The characteristics of the particles (e.g., their size).
  • The degradation rate of the efficiency of the capture mechanism caused by loading.
  • Whether some of the air entering the unit bypasses the internal capture mechanism.
  • How well the air leaving the device is mixed with air in the room before reentering the device.

In-duct Systems

Only limited information is available on the performance of wholehouse in-duct air cleaning systems in removing particles. Their efficiency for particle removal can be assessed by three standard methods: the weight arrestance test, the atmospheric dust spot test, and the DOP method in Military Standard 282.

The weight arrestance test, described in the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Standard 52-76l, is generally used to evaluate low efficiency filters designed to remove the largest and heaviest particles; these filters are commonly used in residential furnaces and/or air-conditioning systems or as upstream filters for other air-cleaning devices. For the test, a standard synthetic dust is fed into the air cleaner and the proportion (by weight) of the dust trapped on the filter is determined. Because the particles in the standard dust are relatively large, the weight arrestance test is of limited value in assessing the removal of smaller, respirable-size particles from indoor air.

The atmospheric dust spot test, also described in ASHRAE Standard 52-76, is usually used to rate medium efficiency air cleaners (both filters and electronic air cleaners). The removal rate is based on the cleaner’s ability to reduce soiling of a clean paper target, an ability dependent on the cleaner removing very fine particles from the air. Exhibit 1 shows typical applications and limitations of filters rated using the ASHRAE Standard 52-76 atmospheric dust spot test2.

Military Standard 2823 [i.e., the percentage removal of 0.3 micrometer (µm) particles of dioctylphthalate (DOP)] is used to rate high efficiency air filters, those with efficiencies above about 98 percent. [The term “HEPA” (high efficiency particulate air) filter is commonly encountered in the marketplace. These filters are a subset of high efficiency filters and are typically rated using the DOP method. One standard-setting organization defines a HEPA filter as having a minimum particle collection efficiency of 99.97 percent by this testing method4.]

Although the above standard tests yield information on the expected efficiency of rated air cleaning devices in removing particles from the air flowing through them, few studies have been conducted to obtain actual effective removal rates in houses in which the devices were installed. The efficiency of in-duct devices may vary based on the air flow rate and the particulate matter load. Effectiveness may also be decreased if air exiting the heating and/or air-conditioning system is not well mixed with room air before reentering the system. This can happen if air return and intake vents are too closely spaced within the home. In addition, the type of device chosen should depend not only on its efficiency but also on its dust-holding capacity and its resistance to air flow, two additional factors assessed by ASHRAE Standard 52-76.

Finally, it should be noted that ASHRAE Standard 52-76 addresses the overall efficiency of removal of a complex mixture of dust. However, removal efficiencies for different size particles may vary widely. Recent studies by EPA, comparing ASHRAE ratings to filter efficiencies for particles by size, have shown that efficiencies for particles in the size range of 0.1 to 1 µm are much lower than the ASHRAE rating5. A filter with an ASHRAE dust spot rating of 95 percent only removed 50-60 percent of particles in the 0.1 to 1 µm size range. Many of the respirable-size particles in indoor air (e.g., cigarette smoke) appear to be in this size range.

In contrast to the ASHRAE Standard 52-76 ratings, efficiencies derived by the DOP method in Military Standard 282 are expected to be more representative of capture efficiencies for respirable-size particles.

Exhibit 1. Filter Applications for In-duct Systems Based on ASHRAE Atmospheric Dust Spot Test

Air Cleaner Efficiency Ratings
10% 20% 40% 60% 80% 90%
Used in window air conditioners and heating systems

Useful on lint.

Somewhat useful on ragweed pollen.

Not very useful on smoke and staining particles.

Used in air conditioners, domestic heating, and central air systems.

Fairly useful on ragweed pollen.

Not very useful on smoke and staining particles.

Used in heating and air conditioning systems, and as pre-filters to high efficiency cleaners.

Useful on finer airborne dust and pollen.

Reduce smudge and stain materially.

Slightly useful on non-tobacco smoke particles.

Not very useful on tobacco smoke particles.

Use same as 40%, but better protection.

Useful on all pollens, the majority of particles causing smudge and stain, and coal and oil smoke particles.

Partially useful on tobacco smoke particles.

Generally used in hospitals and controlled areas.

Very useful on particles causing smudge and stain, and coal and oil smoke particles.

Quite useful on tobacco smoke particles.

Use same as 80%, but better protection.

Excellent protection against all smoke particles.

1. Efficiency rating by ASHRAE Standard 52-76 atmospheric dust spot test.

Adapted from Reference #2.

Portable Units

Studies have been performed on portable air cleaners assessing particle removal from the air in room-size test chambers or extensively weatherized or unventilated rooms. All of the tests addressed removal of cigarette smoke particles6-14; some limited testing with larger particles (fine automotive test dust, airborne cat allergen, and pollen) was also performed9,l2,l4. The test methods used by each group of investigators varied.

The studies show varying degrees of effectiveness of portable air cleaners in removing particles from indoor air. In general, units containing either electrostatic precipitators, negative ion generators, or pleated filters, and hybrid units containing combinations of these mechanisms, are more effective than flat filter units in removing cigarette smoke particles. Effectiveness within these classes varies widely, however.

Again, important factors, in addition to the efficiency of the device itself are the air flow rate; the particle characteristics; the degradation of efficiency with particulate loading; the bypass of air around the collection mechanisms used; and the size of the room.

In addition, for negative ion generators, the placement of the device and the air circulation in the room affect performance. For removal of larger dust particles, negative ion generators, without additional particle capture mechanisms (e.g., filters), may perform poorly.

The general trend in the market over the past few years has been toward larger, more powerful console-sized models. In recent testsl2, the CADRs for 6 tabletop units ranged from about 50 to 100 cfm for smoke particles, whereas the CADRs for the 21 console units ranged from about 50 to 250 cfm. (However, as discussed later, reemission of chemicals from particles trapped by these devices is of concern.)

In general, placement of any portable device may affect its performance. If there is a specific, identifiable source of pollutants, the unit should be placed so that its intake is near that source. If there is no specific source, the air cleaner should be placed to force cleaned air into occupied areas. In addition, the air cleaner should be located where the inlet and outlet are not blocked by walls, furniture, or other obstructions.

Effectiveness of a unit may also be decreased if air exiting the air cleaner outlet is not adequately mixed with room air before reentering the device.

The use of a single portable unit would not be expected to be effective in large buildings (e.g., apartments or office buildings) with central heating, ventilating, and air-conditioning (HVAC) systems. Portable units are designed to filter the air in a limited area (e.g., up to several connected rooms without obstructions to air flow). Air circulated within central HVAC systems may have large effective volumes (e.g., several floors of a building). To clean air in these situations requires the use of either multiple portable units or induct systems designed for the building by HVAC engineers.

Removal of Gaseous Pollutants

Some air cleaners are designed to remove gaseous pollutants as well as particles. However, studies on the effectiveness of portable or residential induct air cleaners in removing gaseous pollutants are limited.

Sorption on solid sorbents is the most frequently used process for removing such contaminants from indoor air. The performance of solid sorbents is dependent on several factors, including:

  • The air flow rate through the sorbent.
  • The concentration of the pollutants.
  • The presence of other gases or vapors (e.g., humidity).
  • The physical and chemical characteristics of both the pollutants and the sorbent (e.g., weight, polarity, size, and shape).
  • The configuration of the sorbent in the device.
  • The quantity of sorbent used and the sorbent bed depth.

Because the rate of sorption (i.e., the efficiency) decreases with the amount of pollutant captured, gaseous pollutant air cleaners are generally rated in terms of the sorption capacity (i.e., the total amount of the chemical that can be captured) and penetration time (i.e., the amount of time before capacity is reached)l5.

Activated Carbon

Activated carbon will adsorb some pollutants even in humid environmentsl5-l6such as those found indoors. However, it does not efficiently adsorb certain pollutants such as volatile, low molecular weight gasesl6,l7.

Sometimes, relatively small quantities of activated carbon will reduce odors in a residence to imperceptible levels. However, because many chemicals produce health effects at levels below those where odors are perceived, removal of odors alone is not an indicator of a healthful environment.

Tests of gaseous pollutant removal by activated carbon have generally been performed using only high concentrations of pollutants, so little information is available on the effectiveness of carbon in removing chemicals present at the low (part per billion, or ppb) concentrations normally found in indoor air. Recent tests performed at EPA measured the adsorption isotherms for three volatile organic chemicals (VOCs) in the 100 to 200 ppb concentration range using three samples of activated carbon. Estimates of the bed depth needed to remove the compounds were made assuming a 150 ppb concentration in the air, an exit concentration of 50 ppb, and a flow rate of 100 cfm across a 2′ X 2′ filter. The results of the study suggest that these chemicals would quickly penetrate the 6 inch deep carbon filters currently marketed for odor control in induct systemsl8. Therefore, the useful lifetime of these filters in removing many indoor air pollutants may be short.

The ability of carbon to reemit pollutants it has trapped from indoor air is also of concern. The National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS), is currently developing a standard method to be used in evaluating the effectiveness of media used for gaseous pollutant removal19. They have reported the results of a study using activated carbon, in which the concentration of toluene in the air flowing into the carbon was varied during the test (from 150 to 0 to 340 to 26 to 0 ppm). The experiment simulates the variations in pollutant levels which would be expected in indoor air situations. They found that toluene initially adsorbed by the media was slowly reemitted each time the pollutant level entering the media dropped. The amount of toluene emitted by the media during the 45-hour experiment was approximately equal to that adsorbed.

Special Sorbents

Special sorbents have been developed to remove specific gaseous pollutants such as formaldehydel5,20. Many of these are chemisorbents, impregnated with chemically active materials, such as potassium permanganate or copper oxide, which will react with one or a limited number of different reactive gaseous pollutants.

Several studies have focused on the removal of formaldehyde in homes using such chemisorbents. These data suggest that large quantities of sorbent and high air flow rates may be required to effectively reduce formaldehyde levels20.

In addition, because chemisorbents are specific for one or a limited number of reactive pollutants, they should not be expected to efficiently reduce pollutants for which they are not specifically designed.

Tests of Portable Units

Testing has been performed recently on gaseous pollutant removal by several portable air cleaners containing activated carbon and/or additional specialized sorbentsl0,ll,l3,21. The CADRs calculated for “hydrocarbons” or inpidual VOCs (excluding formaldehyde) in these studies were generally low, ranging from 0 to 30 cfm. None of four units tested for the removal of dichloromethane removed any of this compound. Lower molecular weight gases, including nitrogen oxides, sulfur dioxide, formaldehyde, hydrogen cyanide, and ammonia, were generally removed at greater rates than the higher molecular weight organic compounds. Nitrogen dioxide removal for eight units where CADR values were reported ranged from 3 to about 94 cfm11,13,21. CADRs were available for only two units for each of the remaining lower molecular weight gases; the highest CADRs reported were for nitrous oxide and formaldehyde (approximately 120 cfm in one unit).

In general, units containing specialized sorbents performed better in the removal of gaseous pollutants than those containing activated carbon alone. However, as suggested by the above results, removal rates varied widely between units. In addition, widely differing removal rates were found for the pollutants tested in the same unit; some models that removed larger quantities of one pollutant did not remove much of another.

Several factors were not assessed in the tests of the portable units, making evaluations of the effectiveness of these devices in indoor air environments incomplete. For example, because these tests did not determine the sorption capacity or penetration rates for the air cleaners, it is not known how long the filters would remain effective. Preliminary tests were performed on one air cleaner to assess long-term efficiency in removing NO2(260 ppb) and six VOCs. The VOCs chosen were representative of six classes of VOCs found in indoor air, and the concentrations and relative proportions of the six VOCs were selected to reflect those reported for their respective classes in indoor air. Following testing in a test chamber to determine the initial removal efficiencies for these compounds, the air cleaner was operated intermittently in a home over a two-and-a-half-month period. Followup testing in the test chamber showed a decrease in efficiency of 50 percent or more for each chemical after 160 hours of use (i.e., 15 percent of the manufacturer’s recommended filter lifetime)2l.

Another factor that was not assessed was the effect of additional chemicals in the air (e.g., water) during the removal process. Since indoor air is a complex mixture of chemicals, tests on one or a mixture of several pollutants may not adequately represent removal rates in indoor environments.

In summary, data are too limited at present to assess the overall effectiveness of air-cleaning devices in removing gaseous pollutant mixtures. Although some of the devices which are designed to remove gaseous pollutants may be effective in removing specific pollutants from indoor air, none are expected to adequately remove all of the gaseous pollutants present in the typical indoor air environment. In addition, information is limited on the useful lifetime of these systems.

Removal of Radon and its Progeny

Air cleaning is generally not the preferred approach to reducing health risks associated with radon. When source control techniques are not possible, or do not result in acceptable radon levels, air-cleaning techniques are available to reduce levels of radon gas and its progeny. Studies on the effectiveness of air cleaners in removing these pollutants have focused on either removing radon gas itself or removing the short-lived progeny produced by radon.

Some limited research on the effectiveness of carbon in removing radon gas itself from indoor air suggests that extremely large quantities of carbon would be required. However, some radon removal units which are specifically designed to regenerate the carbon media that they contain can increase the range of situations (area and radon concentration to be treated) where this technique is applicable.

Since the health hazard from radon is associated with the radon progeny, rather than radon gas itself, the effectiveness of air cleaners in removing radon progeny has also been assessed. Although some radon progeny are removed by filtration or electrostatic precipitation, the types of radon progeny not removed from the air may be of relatively greater concern from a health standpoint. In addition, radon gas concentrations are unaffected, and can continue to be a source of radon progeny in areas of the structure that are not effectively treated by the air cleaner. Because uncertainty exists concerning the effectiveness of air cleaners in reducing the health risks associated with radon, EPA neither currently endorses nor discourages their use as a method of reducing radon progeny in indoor air22.

Will Air Cleaning Reduce Health Effects from Indoor Air Pollutants?

As previously discussed, no air-cleaning system is available that will effectively remove all pollutants from indoor air. As such, the use of air cleaners should only be considered when the use of other methods to reduce indoor air pollutants (e.g., controlling specific sources of pollutants or increasing the supply of outdoor air) are not successful in reducing pollutants to acceptable levels.

Under the right conditions, some air-cleaning systems can effectively remove certain particles, although the particles must be suspended in the air as discussed later. Some of the air cleaners containing sorbents may also remove a portion of the gaseous pollutants in indoor air, and may help eliminate some of the hazards from these pollutants, at least on a temporary basis. However, air-cleaning systems are not expected to totally eliminate all of the hazards from gaseous pollutants. In addition, gaseous pollutant removal systems may have a limited lifetime before replacement of the sorbent is necessary. It should also be noted that although some air-cleaning devices may be effective at reducing tobacco smoke particles, many of the gaseous pollutants from tobacco smoke are not expected to be effectively eliminated. In addition, gases may be reemitted from tobacco smoke particles trapped by the air cleanerl7.

The typical air cleaner which does not contain a specialized carbon regenerating device would appear to be ineffective in removing radon gas and, because many questions exist concerning the relative health risks of radon decay products, there are insufficient data to quantify the impact of air cleaning on reducing the risks of lung cancer caused by radon progeny.

There is currently some controversy about how effectively air cleaners alleviate allergic reactions produced by larger particles such as pollen, house dust allergens, some molds, and animal dander. In February 1987, an ad hoc committee convened at the request of the Food and Drug Administration and several manufacturers of air-cleaning devices met to determine whether standards could be recommended for portable air cleaners and concluded that “the data presently available are inadequate to establish the utility of these devices in the prevention and treatment of allergic respiratory disease.”23

Pollen and house dust allergens settle out rapidly from the air if not disturbed and suspended in the air again. Because only a small proportion of these allergens is generally suspended in the air, air cleaners may be relatively ineffective in their removal.

Although other allergen particles, such as animal dander, do not settle as rapidly as pollen and house dust allergens, the amount of allergen associated with surfaces either due to direct deposition or to settling will generally far exceed that in air. However, because larger quantities of these allergens may remain in air, air cleaning may be more effective in reducing these particles under some circumstances23. On the other hand, use of an air cleaner may disturb allergen which has settled on surfaces, resulting in a decrease in overall allergen removal from the airl4.

Published reports reviewed by the ad hoc committee were limited in scope, but indicated that the exposure to allergens originating outdoors during the warm months (i.e., pollen and some molds) can best be prevented by the use of an air conditioner, with only minimal additional benefit from an air cleaner. The effectiveness of air conditioning in reducing these pollutants was related to the exclusion of outdoor air (often 10 percent of the output of chilled air) and, in the case of molds, also to a reduction in humidity.

With subjects sensitive to house dust allergen, the use of impermeable coverings on the mattresses appeared to be as effective as the use of a laminar flow air-cleaning system above the bed. Based on these results, the committee felt that “air-cleaning devices should be considered only if symptoms remain severe despite other avoidance measures and there is reason to believe that a significant load of airborne allergens is present.”23

What Additional Factors Should Be Considered in Deciding Whether to Use an Air Cleaner?

Several factors other than the ability of air-cleaning devices to reduce airborne pollutant concentrations should be considered when making decisions about using air cleaners. These include:

Installation. Use, and Need for Maintenance

The air-cleaning unit may have certain installation requirements that must be met, such as an adequate and accessible power supply or the need for access during use, repairs, or maintenance.

After installation, operating and maintenance procedures specified by the manufacturer need to be followed to assure adequate performance from the air cleaner. Filters and sorbents must be cleaned or replaced and plates or charged media of electronic air cleaners must be cleaned, sometimes frequently. To avoid electrical and mechanical hazards, the purchaser should ascertain that the unit is listed with Underwriters Laboratories (UL) or another recognized independent safety testing laboratory.

In addition, during cleaning an effort needs to be made to ensure pollutants do not get reemitted back into the air. For example, when filters are removed, excessive movements or air currents should be avoided to prevent redistribution of particles into the air.


Cost may also be a consideration. Major costs include the initial purchase of the unit, maintenance costs (i.e., cleaning and/or replacement of filters and other parts), and operating costs (e.g., costs for electricity).

In general, the most effective units (e.g., those with high air flow rates and efficient particle capture systems) are also the most costly. Maintenance costs vary depending on the device, and should be considered before choosing a particular unit. In comparison to purchase and maintenance costs, operating costs for portable units (e.g., costs for electricity) are negligiblel2.

Production or Redispersal of Pollutants

Another consideration is whether some units will produce new pollutants or redisperse old ones. The potential for ion generators and electronic air cleaners to produce ozone, a lung irritant, may be of concern, particularly if electronic air cleaners are not properly installed and maintained7,l5,l6. This requires further study. At least two manufacturers of portable units advertise that their products produce ozone to facilitate removal of harmful gases, but the levels produced by these devices and the possible health effects are not known. Measurable levels of ozone were produced by one portable and two induct electrostatic precipitators in tests by EPA5, and the Agency is conducting research to determine if the concentrations produced by the induct air cleaners are potentially harmful. The Agency recently released the fact sheet, “Ozone Generators That Are Sold As Air Cleaners.” The purpose of this document (which is only available via this web site) is to provide accurate information regarding the use of ozone-generating devices in indoor occupied spaces. This information is based on the most credible scientific evidence currently available.

The production of fine particulate material by electronic air cleaners has also been reported8,ll,24. Also, filters and other particulate control devices may remove particles from air and then may reemit gases and odors from the collected particlesl7, and materials used in the construction of air cleaners may themselves emit chemicals to indoor air (e.g., formaldehyde may be emitted if particleboard is used in the air cleaner housing2l).

Inability to Remove Some Odors

A number of air cleaners tested were found to reduce the levels of cigarette smoke particles in the air. However, the odor of cigarette smoke remained because many of the devices do not contain effective systems to remove the gaseous products of cigarette smoke and because the gaseous products may be adsorbed and later reemitted by articles in the home8,9. To overcome this, some devices scent the air to mask odors, which may lead the occupants of the home to believe that the odor-causing pollutants have been removed.

Possible Effects of Particle Charging

Another factor with respect to ion generators, particularly those that do not trap some of the charged particles, is the effect of particle charging on deposition in the respiratory tract. Experiments have shown a linear increase in particle deposition with charge; therefore, the use of ion generators may not reduce the dose of particles to the lung8.

Soiling of Walls and Other Surfaces

Ion generators are generally designed not to remove particles from the air but to deposit them on surfaces around the room. This results in soiling of walls and other surfaces, especially if the particles charged by the apparatus are not collected on a filter9.


Noise may be a problem with air cleaners containing a fan7,9,l2. Some portable units operating at high speed can produce noise equivalent to a small vacuum cleaner9or that made by light traffic at 100 ft7. Even at low speed, some models produce an annoying hum or whinel2.

What Guidelines are Available to Compare Air Cleaners?

With the exception of the DOP method in Military Standard 2823, used only to rate particle reduction by high efficiency filters, the federal government has not published any guidelines or standards for use in determining how well an air cleaner works in removing pollutants from indoor air. However, standards for rating particle removal by induct or portable air cleaners have been published by two private standard-setting trade associationsl,25. These estimate the efficiency or effectiveness of an air-cleaning device in removing particles from indoor air, and can be used for comparisons among different devices.

Standards for air cleaners now focus only on particle removal. No guidelines or standards are available for use in assessing the comparative ability of air cleaners to remove gaseous pollutants or radon and its progeny, and research is currently inadequate to draw firm conclusions regarding the relative effectiveness of air-cleaning devices in removing such pollutants.

Standards for In-Duct Devices

ASHRAE Standard 52-761 and the DOP method in Military Standard 2823 may be used to estimate the efficiency of induct devices in removing particles. Using the ratings of the ASHRAE Standard 52-76 atmospheric dust spot test, Exhibit 1 can give a general indication of the types of particles which should be removed by a specific air cleaner. These standards can generally be used to compare the performance characteristics of one device with another, but cannot by themselves predict the actual effectiveness of a given unit in use in a residence or its useful lifetime. In addition, as discussed previously, the efficiency of these air cleaners may vary by air flow rate and particle load, and removal of some small respirable size particles may actually be lower than assessed by the ASHRAE atmospheric dust spot test.

(Note: In examining information on ASHRAE ratings, be aware of differences in results from the weight arrestance test and the atmospheric dust spot test. For example, a filter with a weight arrestance of 90 percent may have an atmospheric dust spot efficiency below 40 percent. The ASHRAE weight arrestance test is of limited value in assessing the removal of respirable size particles from indoor air.)

Because higher efficiency pleated filters are much thicker than filters generally used in standard home heating and/or air-conditioning systems, their use results in substantial air resistance, so they cannot be directly incorporated into the standard residential system. Instead, a system must be specially designed with a fan of sufficient power to create the necessary air pressure and with one or more efficient pre-filters Costs for installation of the system, replacement of pre-filters and filters, and system operation should be considered before deciding whether to purchase higher efficiency filters. Again, the purchaser should be aware of the difference between high “arrestance” and high “efficiency,” as provided by the standard tests.

Further information on standards for induct air cleaners can be obtained through a local heating/air-conditioning contractor or from:

Air-Conditioning & Refrigeration Institute (ARI)
4301 North Fairfax Drive, Suite 425
Arlington, VA 22203
(703) 524-8800
(703) 528-3816 (fax)

Standard for Portable Air Cleaners

The Association of Home Appliance Manufacturers (AHAM) has developed an American National Standards Institute (ANSI)-approved standard for portable air cleaners (ANSI/AHAM Standard AC-1-1988)25. This standard may be useful in estimating the effectiveness of portable air cleaners. Under this standard, room air cleaner effectiveness is rated by a clean air delivery rate (CADR) for each of three particle types in indoor air: tobacco smoke, dust, and pollen.

Only a limited number of air cleaners have been certified under this program at the present time. A complete listing of all current AHAM-certified room air cleaners and their CADRs can be obtained from CADR .

Association of Home Appliance Manufacturers (AHAM)
20 North Wacker Drive
Chicago, IL 60606

Exhibit 2 shows the percentage of particles removed from indoor air in rooms of various size by rated CADR, as estimated by AHAM. Because CADR values on air cleaners in the market will vary from the five in the exhibit, the figures are to be used only as a guide to a model’s performance. The exhibit provides estimates of the percent of particles removed by the air cleaner and the total removal by both the air cleaner and by natural settling.

There are other factors to consider in using the ANSI/AHAM ratings. The CADR values reported are based on reducing particle levels from sources which emit the particles intermittently rather than continually. If the source is continual, the devices would not be expected to be as effective as suggested by Exhibit 2. In addition, the values represent performance that can be expected during the first 72 hours of use. Subsequent performance may vary depending on conditions of use. Use and care directions should be followed routinely to get adequate performance from the air cleaner.

Estimated Percentage of Particle Removal for Portable Units
by CADR and by Room Size
Percentage of Particles Removed
Room Size CADR Smoke
(20 min.)
(20 min.)
(10 min.)
5 x 6




9 x 12


12 x 18








18 x 24








20 x 30




-67%- -84% – -40% -86%-
AC=Removal by the air-cleaning device
T= Removal by the air-cleaning device plus natural settling
Note: Estimates ignore the effect of incoming air. For smoke and, to a lesser extent, dust, the more drafty the room, the smaller the CADR required. For pollen, which enters from outdoors, a higher CADR is needed in a drafty room.
Source: Reference26.


Three strategies (in order of effectiveness) that may be used to reduce indoor air pollutants are source control, ventilation, and air cleaning. Air cleaning may achieve an additional reduction in the levels of certain pollutants when source control and ventilation do not result in acceptable pollutant concentrations. However, air cleaning alone cannot be expected to adequately remove all of the pollutants present in the typical indoor air environment.

Air cleaners are usually classified by the method employed for removing particles of various sizes from the air. There are three general types of air cleaners on the market: mechanical filters, electronic air cleaners, and ion generators. Hybrid units, using two or more of these removal methods, are also available. Air cleaners may be in-duct units (installed in the central heating and/or air-conditioning system) or stand-alone portable units.

The effectiveness of air cleaners in removing pollutants from the air is a function of both the efficiency of the device itself (e.g., the percentage of the pollutant removed as it goes through the device) and the amount of air handled by the device. A product of these two factors (for a given pollutant) is expressed as the unit’s dean air delivery rate (CADR).

Portable air cleaners vary in size and effectiveness in pollutant reduction capabilities. They range from relatively ineffective table-top units to larger, more powerful console units. In general, units containing either electrostatic precipitators, negative ion generators, or pleated filters, and hybrid units containing combinations of these mechanisms, are more effective than flat filter units in removing tobacco smoke particles. Effectiveness within these classes varies widely, however. For removal of larger dust particles, negative ion generators, without additional particle capture mechanisms (e.g., filters), may perform poorly.

Pollutants in indoor air may be pided, for convenience, into three groups: particles, gaseous pollutants, and radon and its progeny. Some air cleaners, under the right conditions, can effectively remove small particles which are suspended in air. However, controversy exists as to the efficacy of air cleaners in removing larger particles such as pollen and house dust allergens, which rapidly settle from indoor air. In assessing the potential efficacy of an air cleaner in removing allergens, one should consider the relative contribution of airborne to surface concentrations of the allergens, particularly in the case of pollen and house dust allergens where natural settling may be so rapid that air cleaners contribute little additional effect. Animal dander may settle more slowly although, again, the surface reservoir far exceeds the amount in the air. Furthermore, control of the sources of allergens and, where allergens do not originate outdoors, ventilation should be stressed as the primary means of reducing allergic reactions

Some of the air cleaners containing sorbents may also remove some of the gaseous pollutants in indoor air. However, no air-cleaning systems are expected to totally eliminate all hazards from gaseous pollutants and these systems may have a limited lifetime before replacement is necessary. In addition, air cleaning may not be effective in reducing the risks of lung cancer due to radon.

In choosing an air cleaner, several factors should be considered. These include:

  • The potential effectiveness of the device under the conditions it will be used.
  • The need for routine maintenance, including cleaning and replacement of filters and sorbents.
  • The estimated capital and maintenance cost.
  • The installation requirements (e.g., power, access).
  • The manufacturer’s recommended operating procedures.
  • The possible production or redispersal of pollutants, such as ozone, particles, formaldehyde, and trapped gaseous pollutants.
  • The inability of air cleaners designed for particle removal to control gases and some odors, such as those from tobacco smoke.
  • Possible health effects from charged particles produced by ion generators.
  • Possible soiling of surfaces by charged particles produced by ion generators.
  • The noise level at the air flow rates that will be used.

Finally, one Federal standard, addressing only high efficiency air filters, and two standards provided by independent standard-setting trade associations outside the Federal government may be useful as guidelines in choosing an air cleaner for reduction of particles in indoor air. For induct systems, the atmospheric dust spot test of ASHRAE Standard 52-76 and the DOP method in Military Standard 282 may be used, respectively, to estimate the performance of medium and high efficiency air cleaners. For portable air cleaning systems, ANSI/AHAM AC-1-1988 may be useful in estimating the effectiveness of the units. Similar standards are not currently available to compare the performance of air cleaners in removing gaseous pollutants or radon and its progeny.


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    14. Luczynska CM, Li Y, Chapman MD, Platts-Mills TAE. 1988. Airborne concentrations and particle size distribution of allergen derived from domestic cats (Felis domesticus): Measurements using cascade impactor, liquid impinger and a two site monoclonal antibody assay for Fel d I. Presented to the American Academy of Allergy Meeting, Los Angeles, March 4, 1988.
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Last Modified: April 26, 1999