Hives are red, itchy, swollen areas of the skin. They often appear in clusters with new clusters appearing as others clear. Hives can arise suddenly and may leave as quickly as one or two hours or last as long as 24 hours. Twenty percent of the population has suffered from hives at least once in their lives.
What Causes Hives?
Hives are often triggered by foods or medications. Among the most common foods that cause hives are peanuts, tree nuts (almonds, walnuts, etc.) and shellfish (crab, shrimp, oysters, etc.). Common medications associated with hives include penicillin, sulfa, phenobarbital, and aspirin.
Some types of hives are not triggered by allergy. Cholinergic urticaria is the medical term for hives that appear after an activity that increases the body temperature like hot tub use, exercise, fever, or emotional stress. The hives usually occur as the skin cools after being warmed. Cold-induced hives occur after exposure to cold wind or water and often appear on the lips or mouth. Solar hives are caused by exposure to sunlight or a sunlamp and a reaction can occur within one to three minutes.
Sometimes exercise can trigger hives. With exercise-induced hives, some individuals may develop a lung obstruction and may lose consciousness. This severe reaction is called anaphylaxis and may be fatal. Exercise anaphylaxis is extremely rare.
Hives that continue either daily or frequently for longer than four weeks are called "chronic urticaria". This is usually not caused by allergy, but an allergist is well qualified to evaluate and treat this problem.
Treatment of Hives