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:
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:
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.
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.
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.