An example of red and swollen hives

Hives, medically referred to as urticaria, are red, itchy, raised areas of the skin that appear in various shapes and sizes. They can appear round, in rings, or as patches on the skin, and can afflict any part of the body. An estimated 5% of people will suffer from hives at some point in their lives. Hives tend to change rapidly and move around the body, disappearing in one area and reappearing in another, sometimes within a few hours. Swelling deeper in the skin that may accompany hives is known as angioedema.  Angioedema should be addressed promptly since it can involve the respiratory tract (breathing problems).


There are two types of hives, ordinary and physical.

  • Ordinary hives:

    Ordinary hives flare up suddenly and for no apparent reason. Welts, itchiness and swelling develop, and usually go away within a few hours, only to reappear elsewhere on the body. This process will repeat for days or weeks. If the problem persists for more than 6 weeks, the hives are generally categorized as “chronic.” Chronic hives can last from months to years, and in more than 50% of these cases, the cause cannot be determined.

  • Physical hives:

    Physical hives are those caused by direct stimulation of the skin, such as from cold, heat, sun exposure, pressure, sweating, or exercise. In this case, hives appear directly where the skin was stimulated.


Hives and angioedema form when, in response to histamine, blood plasma leaks out of small blood vessels in the skin. Histamine is a chemical released from cells along the skin’s blood vessels. As noted, the cause of many cases of ordinary hives is unknown. Histamine can be released by triggers such as viral infections, medications, food allergy, or insect stings.


Treatment is aimed at relieving symptoms while the hives subside on their own. Antihistamines are the most commonly used agents, as they oppose the effects of histamine leaked by mast cells.  The main side effect of many antihistamines is drowsiness.