Allergic inflammation immediate allergic reaction or as a Type I allergic reaction. The reaction is caused by the release of histamine and mast cell granule proteins by a process called degranulation, as well as the production of leukotrienes, prostaglandins and cytokines, by mast cells following the cross-linking of allergen specific IgE molecules bound to mast cell FcεRI receptors. These mediators affect nerve cells causing itching, smooth muscle cells causing contraction (leading to the airway narrowing seen in allergic asthma), goblet cells causing mucus production, and endothelial cells causing vasodilatation and edema. The late phase of a Type 1 reaction (which develops 8–12
Allergic contact dermatitis primes and sensitizes the immune system for an allergic response, and an "elicitation phase", in which this response is triggered. As it involves a cell-mediated allergic response, ACD is termed a Type IV delayed hypersensitivity reaction, making it an exception in the usage of the designation "allergic," which otherwise usually refers to type I hypersensitivity reactions. Contact allergens are essentially soluble haptens (low in molecular weight) and, as such, have the physico-chemical properties that allow them to cross the stratum corneum of the skin. They can only cause their response as part of a complete antigen, involving their association with