exposed again to the allergen, the IgE on the mast cells binds the antigen, triggering the mast cells to release histamine and other chemicals from their cytoplasm. These chemicals interact with surrounding tissues, producing inflammation and the typical allergic reaction. IgE antibody production can last for many years, sensitizing the mast cells. Thus, for example, someone who had an allergic reaction to penicillin as a child could still be allergic to the drug as an adult.

Another important term is atopy. Atopy is generally defined as the state of having one or more of a defined group of diseases (allergic rhinoconjunctivitis, allergic asthma, and atopic dermatitis) that are caused by the genetic propensity to produce IgE antibodies to environmental allergens (predominantly from pollens, molds, dust mites, animals, and foods) encountered through inhalation, ingestion, and possibly skin contact. Although everyone produces some IgE, people with a genetic predisposition to allergy (i.e., atopy) produce significant quantities of it.

For epidemiological surveys, atopy is sometimes defined differently, that is, solely by the presence of IgE antibodies to one or more allergens—whether or not clinical disease is present. The population identified by this definition is considerably larger than that defined by disease because a sizable number of asymptomatic persons have such antibodies (this condition is known as asymptomatic atopy).

Thus, an atopic individual is defined differently in different settings and by different researchers as either a person with a particular disease described under atopy or a person with IgE antibody (i.e., positive skin tests). It is obviously important, therefore, that the context and use of the term be well defined in its particular applications and settings. In discussing the published literature in this report, the meaning of the term will correspond to that used in the study being considered.

SCOPE AND ORGANIZATION OF THE REPORT

In addressing the tasks described earlier in the chapter, the committee used the following guidelines to define the scope of its deliberations. First, it focused on airborne allergens, although contact allergens (e.g., cosmetics) and food allergens are also in the home (the second major focus). A second major focus in the scope was the residential environment; the broad topic of industrial/occupational allergens was deemed to be beyond the scope of this report and was not covered in depth. Some attention is given, however, to allergens that are found in nonindustrial work sites such as office buildings, hospitals, and schools. Similarly, some attention is given to selected nonbiological chemicals that have been shown to be allergenic and that are found in residential or nonindustrial work sites (e.g., trimellitic



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