Urticaria is usually an allergic skin reaction mediated by IgE antibodies resulting in local redness, swelling, and itching. Urticaria is characterized by elevated white or yellow blisters surrounded by red, inflamed spots on the skin. Urticaria usually initially causes a burning sensation, which soon turns into intense itching. Apart from these symptoms, the course of the urticaria is unpredictable. The rash may appear suddenly and then disappear just as quickly, or it may persist for weeks or more. It occurs most often on the arms, legs, and torso, but can occur on any part of the body. It sometimes appears on one part of the body and then disappears and appears elsewhere.