Urticaria, Angioedema, Anaphylaxis, and Prurigo

The term allergy refers to an inappropriate immune response to typically harmless substances in the environment called allergens. Allergic skin diseases include disorders that are mediated by immunoglobulin E (IgE), such as urticaria and angioedema, or associated with a cell-mediated allergic response to haptens, such as contact dermatitis. Urticaria is a common pruritic condition that is traditionally classified as acute if symptoms evolve for less than 6 weeks and chronic if they persist for more than 6 weeks. Chronic urticaria can be classified as chronic spontaneous urticaria (lesions occur spontaneously) and inducible urticaria, which includes physical urticarias induced by physical stimuli (dermographism, cold urticaria, heat urticaria, solar urticaria, and pressure urticaria), and cholinergic urticaria, which is not triggered by exogenous physical exposure but is induced by heat and sweating due to physical activity. In this chapter, we also describe prurigo, a group of skin conditions characterized by extremely pruritic skin lesions (papules, nodules, and/or plaques).