What causes hives?

Hives are produced by histamine and other compounds released from cells called mast cells, which are a normal part of skin. Histamine causes fluid to leak from the local blood vessels, leading to swelling in the skin.

Hives are very common. Although they can be annoying, they usually resolve on their own over a period of weeks, and are rarely medically serious. Some hives are caused by allergies to such things as foods, medications, and insect stings, but the large majority of cases are not allergic, and no specific cause for them 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 usually not helpful in preventing hives and for the most part are not necessary.

In rare cases (some hereditary, others caused by bee stings or drug allergy), urticaria and angioedema are accompanied by shock and difficulty breathing. This is called anaphylaxis. Ordinary hives may be widespread and disturbing to look at, but the vast majority of cases do not lead to life-threatening complications.