This fact sheet provides answers to basic questions about air quality in the home. It will explain what causes poor indoor air quality, how it can affect your health, and what you can do to improve the air quality in your home.

The quality of air in residential buildings has become an important issue to homeowners and health professionals. Indoor air pollution studies have identified several contaminants that can be present in indoor air. These include combustion products, volatile organic compounds (including formaldehyde), tobacco smoke, bioaerosols, and pesticides. Proper ventilation and elimination of the sources of these contaminants are important in maintaining good indoor air quality.


Indoor air pollution is usually caused by the accumulation of contaminants from various sources inside a home. Emissions from fireplaces, stoves, cigarettes, cleaning products, newer building materials, and chemicals stored in the home can cause indoor air problems. People living in this type of environment may experience adverse health effects from breathing these contaminants.

Many factors contribute to indoor air pollution. Adding insulation and caulking to weatherize the home to save on energy costs can reduce air circulation and trap contaminants inside the home. Outdoor "make-up air" cannot enter the home and dilute contaminants. This is why health effects caused by indoor air pollution are often called "tight building syndrome" or “sick building syndrome.”

Many people underestimate the extent of the indoor air pollution problem. Air pollution is usually visualized as the black smoke emitted from factories. Little thought is given to tobacco smoke and the by-products of aerosol sprays, paints, cleaners, and pesticides used in the home. To compound the problem, it is estimated that the average American spends 70 percent to 90 percent of his or her time indoors, and more than half that time is spent in the home.


Occupants of homes with poor indoor air quality may complain of symptoms such as headache, eye irritation, fatigue, dry throat, sinus congestion, dizziness, and nausea. Because many illnesses can cause these symptoms, diagnosing sick building syndrome is difficult. Extremely high levels of some contaminants, such as carbon monoxide, can cause more serious illness, including death.


Poor ventilation and specific sources of contaminants in the home cause most indoor air problems. Each of these will be addressed in this section.

1. Ventilation Problems

Poor indoor air quality is generally caused by the lack of adequate ventilation, which results in a buildup of contaminants from sources in the home. The National Institute for Occupational Safety and Health identified inadequate ventilation as the primary problem in more than half the workplace indoor air investigations it has conducted. Investigations conducted in homes by the Illinois Department of Public Health have found the same to be true. These investigations revealed that proper ventilation is important in maintaining good indoor air quality.

Most residential heating, ventilation, and air conditioning (HVAC) systems recirculate indoor air to conserve energy. The current trend in home construction is to reduce air leakage through cracks and other openings in walls, floors, and roofs. The combination of these construction practices and the recirculation of indoor air has led to an increase in indoor air problems. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) recommends that a minimum of 15 cubic feet of outdoor make-up air per minute (CFM) per person be brought into the indoor living areas of residential buildings. The ASHRAE guidelines for make-up air for kitchens and bathrooms in homes are much higher. This fresh make-up air dilutes indoor contaminants and helps exhaust them from the home.

Inadequate maintenance of the HVAC system also may contribute to indoor air quality problems. Ventilation system filters that are not replaced on a regular basis may become clogged, reducing air flow volume, quality, and distribution. They also may become places for bacteria and molds to grow and be distributed throughout the home. Humidifier systems on HVAC systems also must be properly maintained to prevent bacteria and mold contamination.

2. Combustion Products

Combustion products from automobile exhaust, furnaces, water heaters, space heaters, scented candles, oil lamps, wood stoves, fireplaces, and gas stoves that are not properly vented can generate carbon monoxide, nitric oxide, nitrogen dioxide, sulfur dioxide, formaldehyde, and respirable particulates. These combustion products may result in eye, nose, and throat irritation; fatigue; dizziness; and nausea.

Tobacco smoke is also a combustion by-product that affects indoor air quality. Tobacco smoke contains thousands of different compounds, compounds including carbon monoxide, acrolein, formaldehyde, hydrogen cyanide, and respirable particles. Acrolein and formaldehyde are potent irritants that cause a burning sensation in the eyes.

3. Organic Vapors

Many household products release organic vapors that can cause adverse health effects. These effects may include nose and throat irritation, headaches, dizziness, and nausea. Products containing these vapors include paints, strippers, fuels, solvents, pesticides, hobby supplies, cleaners, deodorizers, and disinfectants. Formaldehyde is another organic vapor that can cause similar symptoms. Formaldehyde can be found in new construction materials, such as plywood, paneling, fiberboard, and particle board, and in cigarette smoke and many consumer products.

4. Bioaerosols

A bioaerosol is an airborne product of a biological contaminant. Biological contaminants in the home may include mold, bacteria, viruses, mites, and pollen. Bioaerosols released into the air can be distributed throughout the home by the HVAC system. Bioaerosols can cause infectious diseases such as Legionnaires' disease. They also can cause allergic reactions, including hypersensitivity pneumonitis, allergic rhinitis, and some types of asthma. Symptoms caused by biological pollutants include sneezing, eye irritation, coughing, dizziness, and respiratory infections.

Factors that can contribute to the growth of biological contaminants are wet or moist building materials (carpeting, ceilings, walls) and poorly maintained humidifiers, dehumidifiers, and air conditioners. "Humidifier fever" is a common illness caused by improper maintenance of humidifiers that can produce fever, chills, headaches, and persistent coughs. Various fungi and bacteria grow quickly in the warm, stagnant water inside humidifiers. During operation, these contaminants can be distributed into the air and inhaled by the building occupants. Other possible sources of biological contaminants are pets and household plants.


There are many things you can do to improve the indoor air quality of your home. These include improving overall ventilation and reducing sources of contamination in the home.

1. Improving the Ventilation System

HVAC systems must be properly designed, installed, and maintained to ensure good operation. The following recommendations may improve the ventilation in your home:

Residents can supply additional make-up air to the inside of the home by using mechanical fans when outdoor temperatures are favorable in the spring and autumn. When temperatures are severe during the summer and winter, air-to-air heat exchangers may be installed to supply make-up air. These units exhaust stale, warm air from the house and transfer the heat in that air to fresh air being supplied from the outside. In air-conditioned houses during the summer months, heat is transferred from the incoming warm air to the outgoing air, causing a reduction in the energy required for air conditioning.

Homeowners also can install fans that supply outdoor air directly to the return side of the HVAC system. These fans are usually installed with a timing mechanism or manual control to regulate the amount of outdoor air supplied to the structure. This type of system works effectively to supply make-up air, but it also increases the cost of operating the HVAC system since the air is not cooled or heated before it enters the home.

2. Reducing Combustion Products

The following remedies can reduce exposure to combustion products:

3. Reducing Organic Vapors

The following remedies can reduce exposure to organic vapors:

4. Reducing Bioaerosols

The following remedies can reduce exposure to bioaerosols:


Illinois Department of Public Health
Division of Environmental Health
525 W. Jefferson St.
Springfield, IL 62761
TYY (hearing impaired use only) 800-547-0466

Other contacts for indoor air quality material include--

United States Environmental Protection Agency
Public Information Center
401 M St., SW PM-211B
Washington, DC 20460

American Lung Association
1740 Broadway
New York, NY 10019


Your local American Lung Association

American Society of Heating, Refrigeration, and Air Conditioning Engineers
1791 Tullie Circle NE
Atlanta, GA 30329

National Environmental Health Association
720 S. Colorado Blvd.
South Tower, Room 970
Denver, CO 80222

This booklet was supported in part by funds from the Comprehensive Environmental Response, Compensation, and Liability Act trust fund through a cooperative agreement with the Agency for Toxic Substances and Disease Registry, Public Health Service, U.S. Department of Health and Human Services.

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Environmental Health Home

Illinois Department of Public Health
535 West Jefferson Street
Springfield, Illinois 62761
Phone 217-782-4977
Fax 217-782-3987
TTY 800-547-0466
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