Hives (Urticaria & Angioedema)
An episode of hives may last from a few minutes to several hours to several days to several weeks. Each individual welt should last no more than 24 hours.
Chronic episodes of urticaria last more than six weeks. In many cases, the cause of chronic hives cannot be identified despite detailed testing; in this instance the condition is called idiopathic urticaria. In approximately 50 percent of cases of idiopathic urticaria, the immune system is causing the release of chemicals such as histamine. In other cases, chronic urticaria may be associated with thyroid disease or other hormonal problems. Rarely, chronic urticaria has been associated with cancer. In most cases of chronic urticaria, the hives will gradually disappear over time.
Physical urticaria is due to one or more “physical” causes. The most common reason for long-lasting urticaria is dermographism. These hives appear within a few minutes of scratching along an area of skin. Most often, the rash is linear, following the path taken by the act of scratching. Delayed pressure urticaria is swelling that appears on areas of constant pressure from belts and constricting clothing such as sock bands. Cold urticaria (from exposure to low temperature followed by re-warming) can be severe and life threatening if there is a generalized body cooling, for example after a plunge into a swimming pool. Cholinergic urticaria is due to an increase in body temperature with sweating, exercise, hot showers and/or anxiety. Sun-induced urticaria may occur within a few minutes after exposure to the sun.
Certain types of chronic hives are more painful than itchy. The hives may go away leaving a bruise on the skin, and individual hives may last more than 24 hours. In such cases, the cause may be inflammation of the blood vessels (vasculitis).
A single episode of uncomplicated urticaria does not usually need extensive testing. An episode of hives complicated by swelling or trouble breathing requires immediate evaluation in the emergency room. For uncomplicated urticaria, your physician will evaluate for possible causes. If allergy is suspected, a diary of foods eaten within a few hours before the hives started may be extremely helpful.
Chronic urticaria should be evaluated by an allergist-immunologist. The specialist will take a detailed history about your medical history, your family’s medical history, your work and home environment, and medication you’re taking. In some cases you may need X-rays and/or tests to analyze blood and urine. Allergy skin testing may provide useful information in some cases. Rarely, if food allergies are suspected, skin testing, elimination diet, and/or oral food challenges may be required. When vasculitis is suspected, a skin biopsy may be helpful.
The specific cause of urticaria can be identified in approximately 20 percent of cases. Ongoing research will identify more causes and more effective treatments.
If a causative factor can be identified, the best treatment is to avoid or eliminate that factor. For example, if a problem with a specific food is strongly suspected, then that food should be eliminated from your diet. This will require careful reading of packaged food labels and careful questioning about ingredients in restaurant meals.
Persons with physical urticaria should try to avoid exposure to that physical factor, if possible. Patients with solar urticaria should wear protective clothing and apply a sunblock when outdoors. Loose-fitting clothing will help relieve pressure urticaria. People with cold air urticaria should not swim alone, and those with severe cold urticaria should not swim at all. Cold air exposure should be avoided if possible; warm clothing should be used for unavoidable exposure to cold air. For people with dermographism, avoiding harsh soaps and frequent bathing will reduce the problem of dry skin, which can cause itching and scratching that can aggravate this condition.
Source: American College of Allergy, Asthma and Immunology