The state of having one or more of a defined group of diseases—allergic rhinoconjunctivitis, allergic asthma, and atopic dermatitis—that are caused by a genetic propensity to produce IgE antibodies to environmental allergens encountered through inhalation, ingestion, and, possibly, skin contact. A broader definition, sometimes used for epidemiologic studies, requires only the presence of IgE antibody, regardless of allergic disease.