Hypersensitivity reactions which occur within minutes of exposure to challenging antigen due to the release of histamine which follows the antigen-antibody reaction and causes smooth muscle contraction and increased vascular permeability.

Synonyms: Hypersensitivities, Immediate, IgE-Mediated Hypersensitivity, Hypersensitivity, Atopic, Type I Hypersensitivities, Immediate Hypersensitivity, Type I Hypersensitivity, Hypersensitivity, Immediate, Atopic Hypersensitivities, Atopic Hypersensitivity, Hypersensitivity, IgE-Mediated, IgE-Mediated Hypersensitivities, Hypersensitivity, Type I, Hypersensitivities, IgE-Mediated, Hypersensitivities, Type I, Immediate Hypersensitivities, IgE Mediated Hypersensitivity, Hypersensitivities, Atopic