Urticarial rashes (hives) patients have a severely itchy skin with red lesions that can appear anywhere on the body and be of various sizes. The skin lesions usually last for few hours. Many patients with urticarial rashes may also have angioedema. Angioedema is the sudden development swelling of the skin, subcutaneous tissue, mucosa and submucosa due to an allergic reaction. It commonly affects the face, hands, feet, and also the genitals. Angioedema (like laryngeal edema) can be sometimes serious enough to cause obstruction of the airway making it a medical emergency. Angioedema can be caused by a variety of reasons. The angioedema resulting from allergic reactions are usually associated with urticarial rashes. There is release of histamine from mast cells and other inflammatory agents into the bloodstream as a result of the allergic reaction leading urticaria. There is also dilatation and increased permeability of blood vessels leading to the swelling of the cutaneous or mucosal tissue (angioedema). Angioedema and urticarial rashes in some patients are not mediated by antibodies but due to direct stimulation of mast cells to release histamine