Allergic skin reactions are very common, and it can be difficult to figure out what causes them. There are hundreds of different kinds of rashes that can be caused by many things, such as plants like poison ivy, allergic reactions to a medication or a food, or a response to an illness.


Hives (Urticaria)

Urticaria is another term for "hives." The condition affects an estimated 20 percent of the population at one time or another in their lives. An episode of hives can start as itching, followed by swollen, red welts. The itching may be mild or severe. Scratching, alcoholic beverages, exercise, and emotional stress may worsen the itching.

Urticaria (Hives) Symptoms

Swelling or raised red or white bumps or welts that:

  • Can cover large areas and migrate from one spot to another
  • Itch
  • Range in size
  • Appear anywhere on the body

Angioedema often appears on the face around the eyes, cheeks or lips. This deeper layer of swelling can also occur on hands or feet, genitals, or inside the bowels or throat.

In acute hives, the welts disappear within minutes to a few weeks. Chronic hives last for months or even years.

How long do hives last?

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.

What are the different types of urticaria? Can strep throat cause it?

Acute episodes of urticaria last for six weeks or less. Acute urticaria is generally due to certain foods and additives, medications, insect stings, blood transfusions and infections. Foods such as eggs, nuts and shellfish are common causes of urticaria. Medications such as aspirin and antibiotics (especially penicillin and sulfa) also are common causes of hives. Infections causing hives include the common cold, strep throat, infectious mononucleosis and hepatitis. In most of these cases, when the reason for hives is removed or avoided, the hives resolve. 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 painful 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).

How are causes of urticaria identified?

In some cases, the cause is obvious – a person eats peanuts or shrimp, and then develops hives within a short time. 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 cannot be identified.

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 hives treatments.

Hives Treatment

In most instances, urticaria will improve with medications such as antihistamines. Low-sedating or non-sedating antihistamines are preferred because they are effective with minimal side effects. Frequently, your physician may try a combination of 2 or 3 antihistamines. Severe episodes of urticaria may require temporary treatment with prednisone or a similar corticosteriod medication.

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 hives 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.

How We Can Help

Dr. Judge may begin by taking a detailed history, looking for clues in your lifestyle that will help pinpoint the cause of your symptoms. You'll be asked about your work and home environments, your eating habits, your family's medical history, the frequency and severity of your symptoms, and miscellaneous matters, such as if you have pets. Then, you may require some tests. Skin testing is the easiest, most sensitive and generally least expensive way of making the diagnosis. Another advantage is that results are available immediately. In rare cases, it also may be necessary to do a special IgE allergy blood test for specific allergens.


American Academy of Allergy Asthma and Immunology
American College of Allergy, Asthma, and Immunology