Hives (cont.)

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What causes hives and angioedema?

Hives appears when histamine and other compounds are released from cells called mast cells, which are normally found in the skin. Histamine causes fluid to leak from the local blood vessels, leading to swelling in the skin.

Hives is very common. Although annoying, hives usually resolves on its own over a period of weeks and is rarely medically serious. Some hives may be caused by allergies to such things as foods, medications, colorings, preservatives and insect stings, but in the majority of cases, no specific cause for it is ever found. Although patients may find it frustrating not to know what has caused their hives, maneuvers like changing diet, soap, detergent, and makeup are rarely helpful in preventing hives unless there is an excellent temporal relationship.

Having hives may cause stress, but stress by itself does not cause hives.

When to visit the doctor

In rare cases (some hereditary, others caused by bee stings or drug allergy), urticaria and angioedema are accompanied by a striking decrease in blood pressure (shock) and difficulty breathing. This is called anaphylaxis and may rapidly become a medical emergency. In this case, a visit to the emergency room or your doctor is necessary. Ordinary hives may be widespread and disturbing to look at, but the vast majority of cases of hives do not lead to life-threatening complications.

What are the different kinds of hives?

Hives fall into two chronological categories: acute urticaria (ordinary hives which resolve after six to eight weeks) and chronic urticaria (which continue longer than six to eight weeks). Since hives is so common and acute urticaria by definition resolves spontaneously, physicians do not generally expend much time or expense to evaluate the cause of hives of less than eight weeks duration.

Medically Reviewed by a Doctor on 7/11/2014

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