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“Hives” is the common name of a skin disorder called urticaria in which itchy bumps of varying sizes appear suddenly anywhere on the body. Between 10 and 20 percent of the United States population will experience an episode of hives at some time in their life, according to the American Academy of Dermatology.
These skin eruptions form when blood plasma leaks out of small blood vessels in the skin, usually as a result of the release of chemicals called histamine. Histamine is released by mast cells (immune system cells) in response to a substance the body believes is harmful. Histamine causes the blood vessels to widen and leak fluid into the surrounding tissue, resulting in redness, swelling and an itching sensation. Allergic reactions, chemicals, foods and medications are all potential triggers for histamine release.
Hives vary greatly in their appearance and an individual hive may also be referred to as a wheal. They can appear anywhere on the body, but most commonly show up on the arms and legs. They are not as common on the palms of the hands or the soles of the feet. Sometimes individual hives join together to form one giant hive. In some cases, hives may be restricted to one area of a person’s body. In other instances, individuals may experience widespread eruptions.
Hives eventually fade, lasting from a few minutes to a few hours. However, new hives may erupt as others disappear several times during episodes. Therefore, although individual hives usually last less than 24 hours, an episode of recurring hives can continue for varying periods. The length of these periods determines if the condition is considered chronic or acute, as follows:
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Acute hives (acute urticaria). Episodes that last for less than six weeks. Acute urticaria usually persists for a few days and is often caused by an allergic reaction to food or a drug. Other potential causes include infections, insect bites, internal disease, pressure on the skin, cold or sunlight.
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Chronic hives (chronic urticaria). Episodes that occur at least twice a week and persist for more than six weeks. According to the American Academy of Allergy, Asthma and Immunology, about 50 percent of patients have symptoms for more than six months and 20 percent exhibit symptoms for over a decade. The cause of chronic hives is often much more difficult to diagnose than that of acute hives and therefore is often not identified. Chronic hives are twice as common in women as in men.
Allergic urticaria may occur when an allergen is inhaled, ingested or comes into direct contact with a person’s skin. But not all hives are the result of an allergic reaction. They can also be caused by:
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Constant pressure on the skin, such as from a belt or shoulder strap
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Environmental factors, such as extremes in temperature
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Irritating chemicals or cosmetics applied to the skin, even if the person is not allergic to these substances
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Infection
Although hives generally cause only discomfort and itching, in rare cases serious swelling occurs in the mouth or throat. Swelling may be severe enough to restrict the person’s ability to breathe and lead to a loss of consciousness. Hives that impair breathing or swallowing require emergency medical attention.
Hives often occur simultaneously with a related but more serious skin disorder called angioedema. According to the Asthma and Allergy Foundation of America, approximately 30 percent of adults with chronic urticaria also have angioedema. Angioedema produces a deeper swelling in the skin, usually around the face, tongue, extremities or genitals. It can lead to death if untreated.
In addition, the presence of some types of urticaria may mean a patient has a higher risk of developing some types of autoimmune thyroid disease.
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