Most people are aware that outdoor air pollution can damage their health, but many do not know that indoor air pollution also can cause significant health effects. U.S. Environmental Protection Agency (EPA) studies of human exposure to air pollutants indicate that indoor levels of pollutants may be 2 to 5 times, and occasionally more than 100 times, higher than outdoor levels. These levels of indoor air pollutants may be of particular concern because most people spend about 90% of their time indoors.

Depending on the source, indoor air pollutants can include biological contaminants (bacteria, molds, mildew, house dust, mites, and pollen), carbon monoxide, lead, nitrogen dioxide, radon and second-hand smoke.

Many sources of indoor air pollution can be found in any home or office, including:

• combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products;
• building materials and furnishings as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, cabinetry or furniture made of certain pressed wood products, and lead-based paints;
• products for household cleaning and maintenance, personal care, or hobbies;
• central heating and cooling systems and humidification devices; and
• outdoor sources such as radon, pesticides, and outdoor air pollution.

The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are signficant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide that one that is properly adjusted.

Inadequate ventilation can increase indoor pollutant levels by failing to bring in enough outdoor air to dilute emissions from indoor sources and to carry indoor air pollutants out of the home. High temperature and humidity levels also can increase concentrations of some pollutants.

Health effects from indoor air pollutants may be experienced soon after exposure or, possibly, years later.

Immediate effects may show up after a single exposure or repeated exposures. These include headaches, dizziness, fatigue, and irritation of the eyes, nose, and throat.

Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply eliminating the person's exposure to the source of the pollution, if it can be identified. Symptoms of some diseases, including asthma, hypersensitivity pneumonitis, and humidifier fever, may also show up soon after exposure to some indoor air pollutants.

The likelihood of immediate reactions to indoor air pollutants depends on several factors. Age and preexisting medical conditions are two important influences. In other cases, whether a person reacts to a pollutant depends on individual sensitivity, which varies tremendously from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well.

Certain immediate effects are similar to those from colds or other viral diseases, so it is often difficult to determine if the symptoms are a result of exposure to indoor air pollution. For this reason, it is important to pay attention to the time and place symptoms occur. If the symptoms fade or go away when a person is away from home, for example, an effort should be made to identify indoor air pollutant sources that may be possible causes. Some effects may be made worse by an inadequate supply of outdoor air or from the heating, cooling, or humidity conditions prevalent in the home.

Long-term health effects from exposure to indoor air pollutants may show up either years after exposure has occurred or only after long or repeated periods of exposure. These effects, which include some respiratory diseases, heart disease, and cancer, can be severely debilitating or fatal.

It is prudent to try to improve the indoor air quality in your home even if symptoms are not noticeable. While pollutants commonly found in indoor air are responsible for many harmful effects, it is uncertain what concentrations or periods of exposure are necessary to produce specific health problems. People also react very differently to exposure to indoor air pollutants. Further research is needed to better understand which health effects occur after exposure to the average pollutant concentrations found in homes and which occur after exposure to higher concentrations for short periods of time.

In Idaho, the Bureau of Community and Environmental Health of the Idaho Department of Health and Welfare is responsible for informing and educating citizens about human health risks associated with exposure to indoor contaminants and ways to prevent or reduce exposure. Current issues on which the Bureau is focused include radon, mold, and indoor environment triggers of asthma such as tobacco smoke.

For concerns about indoor air quality, contact the Bureau at:

Idaho Department of Health and Welfare

Bureau of Environmental Health and Safety
450 W. State Street
Boise, ID 83702
(208) 334-6584

Indoor air quality for businesses and industry is regulated by the Occupational Safeety and Health Administration (OSHA). OSHA sets permissible exposure limits (PELs) to protect workers against the health effects of exposure to hazardous substances. To date, approximately 500 PELs have been established to regulate the amount or concentration of a substance in the air.

For industrial indoor air quality concerns in Idaho, contact:

Occupational Safety and Health Administration
Boise Area Office
1150 North Curtis Road, Suite 201
Boise, Idaho 83706
(208) 321-2960