Urticaria, commonly known as hives, usually strikes suddenly. First the skin itches, and then it erupts into red welts. The itching may be severe, keeping people from working or sleeping. It's a distressing disorder that affects an estimated 20 percent of the population at one time or another in their lives.
Most cases of urticaria are acute, lasting from a few hours to less than six weeks. Some cases are chronic, lasting more than six weeks. The welts may appear in one place, disappear after a short time, then erupt at another spot, then another. They are made worse by scratching. Each individual hive lasts no more than 24 hours.
What kinds of things can trigger attacks of urticaria?
Bouts of urticaria have been traced to such triggers as infections, drugs (including aspirin), certain foods and additives, cold, sun exposure, insect stings, alcohol, exercise, endocrine disorders and emotional stress. In some people, pressure caused by belts and constricting clothing causes eruption. Urticaria may be a response to infection including the common cold, strep throat and infectious mononucleosis.
In the urticaria-prone person, these triggers cause the body to release chemical mediators, including histamine, from cells. Histamine (which causes itchy, runny noses and watery eyes in hay fever sufferers) dilates the walls of blood vessels, allowing fluids to leak out into the surrounding tissues. Swelling and itching are the result.
How are urticaria "triggers" identified?
In some cases, the trigger is obvious—a person eats strawberries or shrimp, and then develops urticaria within a short time. But because there are so many possible causes for urticaria, other cases require determined detective work on the part of the patient and physician. In some cases, the cause is never identified.
A single episode of uncomplicated acute urticaria probably does not need formal evaluation. For patients with recurrent episodes of acute urticaria, with chronic urticaria, or with urticaria complicated by swelling, trouble breathing or other serious problems, an evaluation is recommended. See your regular physician first, in order to evaluate for non-allergic causes of urticaria. If allergy is suspected, keep a diary of foods eaten, any unusual exposures, and when you have hives. Bring the diary with you to the allergist's office.
To unravel the urticaria puzzle, your allergist-immunologist will take a detailed history, looking for clues in your lifestyle that will help pinpoint the cause of your symptoms. You'll be asked about the frequency and severity of your symptoms, your family's medical history, medications you're taking, your work and home environment, and miscellaneous matters.
The allergist will want to review your diary for further clues.
In some cases you may require tests to analyze blood and urine, and other procedures such as x-rays. Skin tests may provide useful information in some cases. Your allergist-immunologist will decide which tests to order based on the different types of urticaria and the suspected cause.
What are the different types of urticaria?
They can be classified into two categories: allergic and non-allergic. Allergic urticaria is the least common form, although it is somewhat more common in children than adults. It is caused by the immune system's overreaction to foods, drugs, infection, insect stings, blood transfusions or other substances. Foods such as eggs, nuts and shellfish, and drugs such as penicillin and sulfa are common causes of allergic or immunologic urticaria. Recent studies also suggest that some cases of chronic urticaria are caused by autoimmune mechanisms, when the patient develops immune reactions to components of his or her skin.
Non-allergic urticaria are those types of urticaria where a clear-cut allergic basis cannot be proven. These take many forms:
- Dermographism is urticaria that develops when the skin is stroked with a firm object.
- Cold-induced urticaria appears after a person is exposed to low temperatures—for example, after a plunge into a swimming pool or when an ice cube is placed against the skin.
- Cholinergic urticaria, which is associated with exercise, hot showers and/or anxiety, is a form of hives that is related to release of certain chemicals from parts of the nervous system that controls such body functions as blood pressure and heart rate.
- Pressure urticaria develops from the constant pressure of constricting clothing such as sock bands, bra straps, belts or other tight clothing.
- Solar urticaria arises on parts of the body exposed to the sun; this may occur within a few minutes after exposure.
Some cases of non-allergic urticaria may be caused by reactions to aspirin and, possibly, certain food dyes, sulfites, and other food additives. In many cases, particularly in chronic urticaria, the trigger for the problem can't be found; in this instance it is called idiopathic urticaria.
Certain types of urticaria are more painful than itchy, may go away leaving a bruise on the skin, and individual hives may last more than 24 hours. In such cases, and selected other situations, a biopsy of the skin may be necessary for diagnosis.
How is urticaria treated?
Your allergist first will prescribe medications, such as antihistamines to alleviate the discomfort. Severe attacks of urticaria can be temporarily relieved by injections of epinephrine; rarely in these cases, corticosteroids may be prescribed for a short period. Other drugs may be required for specific types of urticaria.
If the cause can be identified, the best course of treatment is avoidance of the substance that triggers urticaria. If a problem with a specific food is strongly suspected, then it should be avoided. This may require a careful reading of packaged food labels and inquiry about ingredients in restaurant meals. Persons with solar urticaria should wear protective clothing and apply sunscreen lotions when outdoors. Loose-fitting clothing will help relieve pressure urticaria. Avoid harsh soaps and frequent bathing to reduce the problem of dry skin, which can cause itching and scratching that can aggravate urticaria. Vigorous toweling after a bath may precipitate hives.
Although success of identifying the cause of chronic urticaria varies from clinic to clinic according to patient populations, it usually is no higher than 20 percent of cases. Chronic urticaria may last for months or for years and burn itself out, never to bother the sufferer again. If you have any more questions, your allergist-immunologist will be happy to answer them.
Written by Thomas Scott, MD and Chrishana Ogilvie-McDaniel, MD, board-certified allergists with Via Christi Clinic in Wichita, Kan.