to many diseases and that aeroallergens—allergens that are airborne—are important in disease pathogenesis. For example, allergy to house dust mites and cats increases the risk of childhood asthma four- to sixfold.

There is a coherence to the body of research on these effects that now deserves emphasis: Exposure to indoor allergens is common, as are resultant sensitization and allergic disease. One hundred million Americans are immunologically sensitized to allergens; that is, they have been exposed to a substance that has raised the sensitivity of their immune system in such a way that the system will produce an "allergic response" when it encounters the allergen on subsequent occasions. The number of Americans so sensitized is fourfold more than the number with hypertension; 50 million people in this country will have a disease related to allergy at some time in their life.

With increasing levels of interest and concern about the potential health effects of indoor air, the Environmental Protection Agency's Office of Air and Radiation, in conjunction with the Agency for Toxic Substances and Disease Registry, and three of the institutes at the National Institutes of Health—the National Institute of Allergy and Infectious Diseases, the National Institute of Environmental Health Sciences, and the National Heart, Lung, and Blood Institute—requested that the Institute of Medicine (IOM) conduct an independent assessment of the public health significance of indoor allergens. Specifically, the IOM was asked to perform the following tasks:

  1. Examine and characterize what is known about the adverse effects on human health caused by indoor allergens and chemicals that elicit allergic reactions.

  2. Characterize the magnitude of these problems nationally and the populations that are commonly affected.

  3. Identify the specific causative agents and their sources.

  4. Assess testing methodologies for indoor allergens, including their applicability and interpretation.

  5. Evaluate the adequacy of the knowledge base that is currently available to physicians on this topic and the need for additional information and research.

The IOM Board on Health Promotion and Disease Prevention responded to the request by establishing a committee with expertise in allergy and immunology, epidemiology, industrial hygiene, mycology, pulmonology, general and family medical practice, engineering, education, and public policy. This report, the product of the committee's deliberations, reviews published epidemiological reports, describes risk factors, and estimates the health impacts of exposure to indoor allergens. It examines clinical diagnostic practices and the measurement of indoor allergen exposures, and discusses the

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