1. Hypersensitivity caused by exposure to a particular antigen (allergen) resulting in a marked increase in reactivity to that antigen on subsequent exposure, sometimes resulting in harmful immunologic consequences. 2. That branch of medicine concerned with the study, diagnosis, and treatment of allergic manifestations. 3. An acquired hypersensitivity to certain drugs and biologic materials. [G. allos, other, + ergon, work]
atopic allergy atopy.