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:
- 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.
- 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:
- Constant pressure on the skin, such as with a belt or shoulder strap
- Environmental factors, such as extremes in temperatures
- Irritating chemicals or cosmetics applied to the skin, even if the person is not allergic to these substances
- 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. Angioedema produces a deeper swelling in the skin, usually around the face, tongue, extremities or genitals. It can lead to death if untreated.
Types and differences of hives
