Type IV, or delayed-type, hypersensitivity is a reaction where tissue damage is the result of T cell-dependent macrophage activation and inflammation Hypersensitivity is an abnormal heightened response to any type of stimulus; it does not normally occur after the initial exposure to an allergen

Type I hypersensitivity, or anaphylactic response, is facilitated by IgE antibodies produced by the immune system in response to allergens like dust mites, animal dander, and pollens The most common type of respiratory allergy is allergic rhinitis

allergic disorder — common pathological condition due to IgE-dependent immunological reactions to an allergen. allergy — inappropriate or exaggerated responses of the immune system to a foreign substance that is usually harmless. allergen — foreign substance that is usually harmless. T cell — cell that assists B cells in the immune response; also called T lymphocyte.