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What are hives or welts?


Hives (Urticaria)

HIVES: Hives have been referred to as welts, nettle rash, and by physicians, urticaria.  They are raised areas of your skin that are warm, very itchy and red.  They can suddenly appear anywhere on the body and last a few hours or as long as 48 hours.  Lesions that are painful/tender and last for greater than 48 hours should be thought of as separate from hives.  New hives can appear as others disappear, giving the impression of persistent lesions.  Individual hives are irregularly shaped and are the size of a dime or nickel, though they often form clusters making larger lesions.  Approximately one in five people will develop hives in their lifetime.
Hives can be caused by allergic or non-allergic mechanisms.  In a majority of chronic cases, the exact cause remains unknown.  A common cause of hives is dermatographism. It is caused by stroking of the skin or rubbing as occurs with scratching or tight-fitting garments.

Often hives are caused by an adverse reaction to some food or durg.  Foods likely to cause hives include nuts, tomatoes, shellfish, and berries.  Drugs often responsible for producing hives are penicillin, sulfa, anticonvulsants, phenobarbital and aspirin.

A small percentage of cases are classified as the physical urticarias. Cholinergic urticaria describes those hives that develop following activities which increase the body’s temperature and with exposure to warmth or heat. Cold-induced urticaria occurs after exposure to cold wind or water.  Another type of physical urticaria is solar urticaria caused by exposure to sunlight or to a sun lamp.

Exercise is another common cause of hives in which there is no allergic substance involved.  Those individuals affected can also develop respiratory obstruction and/or lose consciousness.  Such a severe reaction is called exercise-induced anaphylaxis. It has been recently appreciated that the combination of exercise and consumption of a food can together cause hives or anaphylaxis whereas individually exercise or the food is harmless.

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