Hives, also known as urticaria, are red, itchy swollen areas of the skin and may affect 20 percent of people at some time during their lifetime. Hives can appear suddenly and last for a few hours. Sometimes, hives may last for over a day. There are two types of hives defined by how long they last.

Acute hives last six weeks or less and are generally caused by the following:

• • Foods and additives: milk, egg, wheat, soy, peanut, tree nuts, fish and shellfish.
• • Medications: antibiotics, aspirin, NSAIDS(ibuprofen, naproxen)
• • Infections: viral infections such as the common cold, urinary tract infections, strep throat
• • Inhalants: pollen, dust mites, pet dander
• • Insect stings
• • Underlying systemic disorders: thyroid dysfunction, autoimmune disorders (lupus)

In most cases, acute hives resolve when the cause is avoided or treated.

Chronic hives last more than six weeks. In many cases, the cause of chronic hives cannot be identified despite detailed history and testing. This condition is called idiopathic urticaria. The immune system is the cause of about 50 percent of hives that are not identified. In some cases, chronic hives may be associated with thyroid disease, other hormonal problems, or rarely cancer. In most cases, chronic hives will gradually disappear over time.

One type of chronic hives is caused physical urticaria in which hives can have one or more physical cause. These may include:

• Dermatographism. This is a common cause for chronic hives. Hives appear within a few minutes along the path of rubbing or scratching and usually resolve within an hour.
• Pressure-induced urticaria. Hives can also appear as red swelling caused by belts and constrictive clothing.
• Cold-induced urticaria. Hives may be caused by heat or cold. Hives can be caused by exposure to cold temperature followed by re-warming. This can be severe and life threatening if there is a general body cooling.
• Cholinergic urticaria .These hives are due to an increase in body temperature and are often caused by exercise, hot showers, or emotional stress.
• Solar urticaria. Hives may occur within a few minutes after exposure to the sun.

Inflammation of the blood vessels, called vasculitis, can also cause hives. These hives are more painful than itchy. These painful hives may leave a bruise on the skin and often last more than 24 hours.

What causes hives?

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 hives, other cases require detective work by the patient and physician. In some cases, the cause cannot be identified.

When hives involve swelling of the tongue or trouble breathing, immediate evaluation in the emergency room is required.

A single episode of hives does not usually need extensive testing. If hives reoccurs, an evaluation of possible causes is suggested. If food allergy is suspected, a diary of foods eaten within a few hours before the hives started may be extremely helpful.

Chronic hives should be evaluated by an allergist. A detailed medical history as well as exposures from work and home environment and current medications are reported the evaluation. In some cases you may need allergy skin testing, blood tests and urine tests. Allergy skin testing may provide useful information in some cases. In cases where vasculitis is suspected a skin biopsy may be helpful.

The specific cause of chronic hives can be identified in about 20 percent of cases. Ongoing research will allow us to identify more causes and more effective treatments for hives.

How can hives be treated?

In most cases, hives will improve with medications such as antihistamines. They are effective with fewer side effects. Frequently, several antihistamines are necessary for the treatment for hives. Severe episodes of urticaria may require temporary treatment with prednisone, a similar corticosteroid medication or immune modulator.

If there is associated swelling of the tongue or lips, or trouble breathing, an epinephrine self-injector will be prescribed.

If the cause of hives can be identified, the best treatment is to avoid or eliminate it.

• Foods: If a specific food is strongly suspected, then you should not eat that food. This will require you to carefully read packaged food labels and question restaurant staff about ingredients in meals.
• Rubbing or scratching: Avoid harsh soaps and tight clothing. Frequent bathing may reduce the problem of dry skin, which can cause itching and scratching that can aggravate this condition.
• Constant pressure: Loose-fitting clothing will help relieve hives caused by pressure urticaria.
• Change in temperature: If your hives are caused by cold, you should not swim alone. Cold air exposure should be avoided if possible, and warm clothing should be worn.
• Sun exposure: Wear protective clothing and apply sun block when outdoors.
• Medications: If you have a problem with a specific medication, stop taking it.