Hives have been referred to as whelps, nettle rash, and, by physicians, urticaria. They are raised areas of your skin that are warm, very itchy and red. They can suddenly appear anywhere on the body and last a few hours or as long as 48 hours. Lesions that are painful/tender and last for greater than 48 hours should be thought of as separate from hives. New hives can appear as others disappear, giving the impression of persistent lesions. Individual hives are irregularly shaped and are the size of a dime or nickel, though they often form clusters making larger lesions. Approximately one in five people will develop hives in their lifetime.

What causes hives?

Hives can be caused by allergic or non-allergic mechanisms. In a majority of chronic cases, the exact cause remains unknown.

A common cause of hives is dermatographism. It is caused by stroking of the skin or rubbing as occurs with scratching or tight-fitting garments.

Often hives are caused by an adverse reaction to some food or drug. Foods likely to cause hives include nuts, tomatoes, shellfish and berries. Drugs often responsible for producing hives are penicillin, sulfa, anticonvulsants, phenobarbital and aspirin.

A small percentage of cases are classified as the physical urticarias. Cholinergic urticaria describes those hives that develop following activities which increase the body's temperature and with exposure to warmth or heat. Cold-induced urticaria occurs after exposure to cold wind or water. Another type of physical urticaria is solar urticaria caused by exposure to sunlight or to a sun lamp.

Exercise is another common cause of hives in which there is no allergic substance involved. Those individuals affected can also develop respiratory obstruction and/or lose consciousness. Such a severe reaction in called exercise-induced anaphylaxis. It has been recently appreciated that the combination of exercise and consumption of a food can together cause hives or anaphylaxis whereas individually exercise or the food is harmless.

What are chronic hives?

By definition hives that continue to recur for greater than six weeks are considered chronic. Rarely is an identifiable etiology for the hives discovered. Because of the remote possibility of an underlying pathologic process, such as infection, abnormal thyroid gland function, malignancy or rheumatoid arthritis, a review of your health history and limited blood testing directed toward these entities is routine practice. Fortunately, most cases (~ 75%) resolve within one year. Therapy is symptomatic, aiming to reduce itching while the hives run their course.

What is angioedema?

While hives develop on the skin's surface, angioedema is a swelling of the deeper layers of the skin. It most often occurs on the hands, feet, genitals and face. In severe cases, normal breathing or swallowing can be blocked and emergency measures must be taken. This can occur if a person is extremely allergic to a specific food or drug.

Hives and angioedema may appear together or separately on the body. Angioedema usually lasts one or two days, and may reappear with or without hives over an indefinite period of time. The causes of angioedema are similar to those for urticaria, including medications, physical stimuli such as pressure and vibration, and infections. Unfortunately, in the majority of instances, a true etiology is never uncovered.

Hereditary angioedema is a rare inherited disease that can be fatal in some cases and in this respect differs form other types of chronic angioedema. Swelling can occur in the airways, such as the larynx, tongue and throat, as well as on the face and extremities. It has been demonstrated that a blood protein deficiency is the cause of this inherited illness.

How can hives be treated?

Avoidance of the foods, drugs, or other provoking factors is recommended whenever possible. Antihistamines are often used to treat recurrent episodes.

If the hives do not respond to the antihistamines, many allergists will utilize corticosteroid drugs, such as prednisone, which are given in conjunction with the antihistamines. Most patients will improve with steroid treatment, but if at all possible, they should be avoided for chronic use. Nevertheless, steroids can be used to treat severe chronic hives with minimal side effects, but this requires careful supervision.

In acute cases, where angioedema is involved, adrenaline injections may be necessary to alleviate the swelling. Researchers have found that hereditary angioedema can be effectively treated with male hormones.