Allergies are inflammatory conditions resulting from an allergen (or antigen) producing an adverse immune reaction involving the antibody immunoglobulin E (IgE). Hypersensitivity disorders mediated by IgE include: atopic diseases (i.e., allergic rhinitis, allergic conjunctivitis, atopic dermatitis, and allergic asthma), some cases of urticaria, some cases of digestive allergy, and systemic anaphylaxis. The response to the allergen is determined by the duration, route (i.e., by inhalation, contact, ingestion, or injection), amount of expo¬ sure, and other environmental and host factors (e.g., genetic susceptibility). Allergies affect more than 20% of the population in the United States, with allergic rhinitis having a prevalence rate of 59.7 cases per 1,000. Rhinitis is the most common condition in children under the age of 18 years. Asthma, which occurs at a rate of 42.5 cases per 1,000, frequently co-occurs with allergic rhinitis. The prevalence for digestive allergies is 25.1 cases per 1,000, and for eczema and other skin allergies it is 32.9 cases per 1,000.