Hypersensitivity, Immediate (Atopic Hypersensitivity; Hypersensitivity, Atopic; Hypersensitivity, Type I; Type I Hypersensitivity; IgE-Mediated Hypersensitivity)
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.