What are hives?

Hives are red, very itchy, swollen areas of the skin. They can vary in size from as small as a pencil eraser to as large as a dinner plate, and may join together to form larger swellings. Hives, which are also known as urticaria, arise suddenly and may leave quickly in one to two hours. They often appear in clusters, with new clusters appearing as other areas clear.

Hives do not leave a permanent mark on the skin and over 20 percent of the population has suffered an eruption of hives at some point in their lives.

There are several different types of hives, including:

  • Dermatographism: occurs in five percent of the population. The hives are caused by stroking or rubbing the skin, and often occur after scratching, or when tight-fitting clothes rub the skin.
  • Cholinergic urticaria: hives that can develop after activities which increase the body's temperature. Activities that can cause this include warm baths or showers, jacuzzi or hot tub use, exercise, a fever or emotional stress. It has been estimated that five to seven percent of patients who have hives experience cholinergic urticaria.
  • Cold-induced hives: occur after exposure to cold wind or water. Hives may appear on limbs and generally on any exposed area. Cold water or liquids or frozen foods such as ice cream can provoke symptoms on the lips or in the mouth.
  • Solar hives: caused by exposure to sunlight or to a sunlamp. A reaction can occur within one to three minutes.

Visit the Vaccine Education Center for pictures and additional information about hives and other rash-related illnesses.

Causes of hives

Hives are formed when blood plasma leaks out of small blood vessels in the skin. This leakage is caused by the release of a chemical called histamine.

Histamine is released from special cells called "mast cells." These cells lie along the blood vessels in the skin. Allergic reactions, chemicals in foods and in medications can cause histamine release. Often it's impossible to find out what triggered a histamine release, and thus why hives are forming.

Hives lasting less than six weeks are called "acute urticaria." With this type of hives, the cause can often be found. Certain foods, medications, viruses and other illness, and even things in your home (cats, dogs, dust) can cause hives. Insect bites and internal diseases may also be responsible.

Sometimes hives will occur in individuals repeatedly without an obvious cause. This is called "chronic urticaria." While mainly a nuisance and not associated with other serious internal disease, the exact mechanism for this condition is not known, and the hives usually disappear on their own, though it may take months to years. Frustration is common, since efforts at attempting to identify an underlying cause are usually not revealing.


The most common foods that cause hives are nuts, peanuts, fish, shellfish, eggs and milk. Fresh foods cause hives more often than cooked foods. Food dyes do not typically cause hives. Hives may appear within minutes or up to two hours after eating, depending on where the food is absorbed in the digestive tract.


Almost any prescription or over-the-counter medication can cause hives. Medications often responsible for producing hives are penicillin, sulfa drugs, aspirin and ibuprofen (for example, MOTRIN and ADVIL). Also, antacids, vitamins, eye and ear drops, laxatives or any other non-prescription item can be a potential cause of hives.


Dust, animals or molds in your environment can cause hives. Detergents, fabric softeners and hair sprays often cause contact dermatitis.


Some affected individuals can also develop lung obstruction and/or lose consciousness. Such a severe reaction is called exercise-induced anaphylaxis. 

Treatments for hives

Avoiding the foods, drugs, or other provoking factors is recommended whenever possible. Antihistamines are used to treat recurrent episodes. Hydroxyzine (ATARAX) and cetrizine (ZYRTEC) are especially effective for the treatment of cholinergic urticaria. Cyproheptadine (PERIACTIN) is used to treat cold-induced hives. If the hives do not respond to the antihistamines, sometimes corticosteroid medications will be used in conjunction with the antihistamines.


Reviewed by: Allergy Section
Date: December 2003