ALLERGY

1. A state of hypersensitivity induced by exposure to a special antigen (allergen) resulting in deleterious immunologic reactions on subsequent exposures, the term is generally used to refer to hypersensitivity to an environmental antigen (atopic allergy or contact dermatitis) or to drug allergy. The original importance, now obsolete, included all states of altered immunologic reactivity, immunity as well as hypersensitivity. Gell and Coombs used the term allergic reaction to mean any deleterious immunologic reaction causing tissue injury. 2. The medical specialty dealing with diagnosis and treatment of allergic disorders.