FIGURE 3 Development of allergic disease, illustrated schematically. A genetically susceptible individual is exposed to an allergen and becomes immunologically sensitized. At this stage the person is asymptomatic, but the sensitization may be detected by skin tests or laboratory tests. Over time, a proportion of sensitized individuals will develop one of a group of allergic diseases. Exposure to allergen is understood to be a major factor at each stage of the pathogenesis of these diseases.

MAGNITUDE OF THE PROBLEM

The most common allergic diseases caused by indoor allergens are allergic rhinitis, sinusitis, asthma, and allergic skin diseases (dermatitis). Figure 4 shows the generally accepted ranges of prevalence for these conditions in the United States. Based on these and other data, we can predict that one out of five Americans will experience allergy-related illness at some point during their lives and that indoor allergens will be responsible for a significant share of these cases. As such, indoor allergens are a major public health problem in the United States.

Some interesting facts about allergies and the indoor environment follow:

  • More than 50 million Americans—one out of five—suffer from allergic rhinitis (hay fever) and other allergic diseases, many of which are related to exposure to allergens in indoor environments

  • Allergic rhinitis is the single most common chronic disease experienced by humans.

  • The level of allergen exposure in the home relates to the risk of



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