Urticaria, is the most frequent dermatologic disorder. It appears as raised, well-circumscribed areas of erythema and edema involving the dermis and epidermis that are very itchy. Urticaria may be acute (lasting less than 6 wk) or chronic (lasting more than 6 wk). A large variety of urticaria variants exist, including acute immunoglobulin E (IgE)–mediated urticaria, chemical-induced urticaria (non-IgE-mediated), urticarial vasculitis, autoimmune urticaria, cholinergic urticaria, cold urticaria, mastocytosis, Muckle-Wells syndrome, and many others. It results from the release of histamine, bradykinin, leukotriene C4, prostaglandin D2, and other vasoactive substances from mast cells and basophils in the dermis. The mainstay is avoidance of further exposure to the antigen and antihistamines.