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DefinitionHives are raised, often itchy red welts on the surface of the skin. They are usually an allergic reaction to food or medicine.
Causes, incidence, and risk factors
When you have an allergic reaction to a substance, histamine and other chemicals are released into your bloodstream, causing itching, swelling, and other symptoms. Hives are a common reaction, especially in people with other allergies like hay fever.
When swelling or welts occur around the face, especially the lips and eyes, it is called angioedema ; swelling from angioedema can also occur around your hands, feet, and throat.
Many substances can trigger hives:
Hives may also develop from:
The welts may enlarge, spread, and join together to form larger areas of flat, raised skin. They can also change shape, disappear, and reappear within minutes or hours. The welts tend to start suddenly and resolve quickly. When you press the center of a red welt, it blanches (turns white).
Signs and testsYour doctor can tell if you have hives by the appearance of your skin. If you have a history of an allergy, then the diagnosis is even more obvious. Occasionally, skin or blood tests are performed to confirm that this was an allergic reaction and to test for the substance that caused your allergic response.
Treatment may not be needed if the hives are mild. They may disappear on their own. To reduce itching and swelling:
If your reaction is severe, especially if the swelling involves your throat, you may require an emergency shot of epinephrine (adrenaline) or steroids. Hives in the throat can obstruct your airway, making it difficult to breathe.
Expectations (prognosis)Hives may be uncomfortable, but they generally are harmless and disappear on their own. In most cases, the exact cause of hives cannot be identified.
Calling your health care provider
Call 911 if you experience:
Call your health care provider if the hives are severe, uncomfortable, and do not respond to self-care.
Update Date: 10/3/2003Jacqueline A. Hart, M.D., Department of Internal Medicine, Newton-Wellesley Hospital, Boston, Ma. and Senior Medical Editor, A.D.A.M., Inc. Previously reviewed by Michael Lehrer, M.D., Department of Dermatology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network (4/17/2003).
Last updated: Tue, 06 Jan 2009 00:20:03 GMT