Mast cells are a type of innate immune cell in connective tissue and the mucous membranes. They are intimately associated with defence against pathogens and wound healing. They are also often associated with allergy and anaphylaxis. When activated, mast cells rapidly release characteristic granules, rich in histamine and heparin, along with various hormonal mediators, and chemotactic cytokines into the environment. Histamine dilates blood vessels, causing the signs of inflammation, and recruits neutrophils and macrophages.