Hives

Definition

Hives is an allergic skin reaction causing localized redness, swelling, and itching .

Description

Hives is a reaction of the body's immune system that causes areas of the skin to swell, itch, and become reddened (wheals). When the reaction is limited to small areas of the skin, it is called urticaria. Involvement of larger areas, such as whole sections of a limb, is called angioedema.

Demographics

Many children and adults experience hives at various times during their lives. As hives is not a reportable event, no accurate prevalence statistics are available.

Causes and symptoms

Hives is an allergic reaction. The body's immune system is normally responsible for protection from foreign invaders. When it becomes sensitized to normally harmless substances, the resulting reaction is called an allergy. An attack of hives is set off when such a substance, called an allergen, is ingested, inhaled, or otherwise contacted. It interacts with immune cells called mast cells, which reside in the skin, airways, and digestive system. When mast cells encounter an allergen, they release histamine and other chemicals, both locally and into the bloodstream. These chemicals cause blood vessels to become more porous, allowing fluid to accumulate in tissue and leading to the swollen and reddish appearance of hives. Some of the chemicals released sensitize pain nerve endings, causing the affected area to become itchy and sensitive.

A wide variety of substances may cause hives in sensitive people, including foods, drugs, and insect bites or stings . Common culprits include:

nuts, especially peanuts, walnuts, and Brazil nuts
fish, mollusks, and shellfish
eggs
wheat
milk
strawberries
food additives and preservatives
penicillin or other antibiotics
flu vaccines
tetanus toxoid vaccine
gamma globulin
bee, wasp, and hornet stings
bites of mosquitoes, fleas, and scabies

Urticaria is characterized by redness, swelling, and itching of small areas of the skin. These patches usually grow and recede in less than a day but may be replaced by others in other locations. Angioedema is characterized by more diffuse swelling. Swelling of the airways may cause wheezing and respiratory distress. In severe cases, airway obstruction may occur.

When to call the doctor

A doctor or other healthcare professional should be called when hives do not spontaneously clear within a day of their appearance or when they include swelling of the throat. If the reactions are severe, as in anaphylactic reaction or shock, immediate medical care is needed.

Diagnosis

Hives are easily diagnosed by visual inspection. The cause of hives is usually apparent but may require a careful medical history in some cases.

Treatment

Mild cases of hives are treated with antihistamines , such as diphenhydramine (Benadryl). More severe cases may require oral corticosteroids, such as prednisone. Topical corticosteroids are not effective. Airway swelling may require emergency injection of epinephrine (adrenaline).

An alternative practitioner will try to determine what allergic substance is causing the reaction and help the person eliminate or minimize its effects. To deal with the symptoms of hives, an oatmeal bath may help to relieve itching. Chickweed ( Stellaria media ), applied as a poultice (crushed or chopped herbs applied directly to the skin) or added to bath water, may also help relieve itching. Several homeopathic remedies, including Urtica urens and Apis ( Apis mellifica ), may help relieve the itch, redness, or swelling associated with hives.

Hives on the back of a young woman's legs. The accompanying inflammation develops as an allergic reaction which ranges in size from small spots to patches measuring several inches across.

Prognosis

Most cases of hives clear up within one to seven days without treatment, providing the cause (allergen) is found and avoided.

Prevention

Preventing hives depends on avoiding the allergen causing them. Analysis of new items in the diet or new drugs taken may reveal the likely source of the reaction. Chronic hives may be aggravated by stress, caffeine , alcohol, or tobacco; avoiding these may reduce the frequency of reactions.

Nutritional concerns

Hives may be triggered or worsened by caffeine or alcohol (in adults), or specific allergenic foods, which depend entirely on the patient. Avoiding these substances may reduce the occurrence of hives.

Parental concerns

Parents should monitor their children to ensure that any attack of hives does not involve the throat area. Young children should be encouraged not to stratch their skin too vigorously. If hives are a recurrent problem, parents should keep track of the foods the child eats in an attempt to discover the allergen.

KEY TERMS

Allergen —A foreign substance that provokes an immune reaction or allergic response in some sensitive people but not in most others.

Wheal —A smooth, slightly elevated area on the body surface that is redder or paler than the surrounding skin.

Resources

BOOKS

Duvic, Madeleine. "Urticaria, Drug Hypersensitivity Rashes, Nodules and Tumors, and Atrophic Diseases." In Cecil Textbook of Medicine , 22nd ed. Edited by Lee Goldman et al. Philadelphia: Saunders, 2003, pp. 2475–85.

Frank, Michael M. "Urticaria and Angioedema." In Cecil Textbook of Medicine , 22nd ed. Edited by Lee Goldman et al. Philadelphia: Saunders, 2003, pp. 1610–3.

Leung, Donald Y. M. "Urticaria and Angioedema (Hives)." In Nelson Textbook of Pediatrics , 17th ed. Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2003, pp. 778–80.

Yancy, Kim B., and Thomas J. Lawley. "Immunologically Mediated Skin Disorders." In Harrison's Principles of Internal Medicine , 15th ed. Edited by Eugene Braunwald et al. New York: McGraw-Hill, 2001, pp. 331–5.

PERIODICALS

Beltrani, V. S. "Urticaria: reassessed." Allergy and Asthma Proceedings 25, no. 3 (2004): 143–9.

Clarke, P. "Urticaria." Australian Family Physician 33, no. 7 (2004): 501–3.

Dice, J. P. "Physical urticaria." Immunology and Allergy Clinics of North America 24, no. 2 (2004): 225–46.

Grattan, C. E. "Autoimmune urticaria." Immunology and Allergy Clinics of North America 24, no. 2 (2004): 163–81.

Lawlor, F., and A. K. Black. "Delayed pressure urticaria." Immunology and Allergy Clinics of North America 24, no. 2 (2004): 247–58.

Rumbyrt, J. S., and A. L. Schocket. "Chronic urticaria and thyroid disease." Immunology and Allergy Clinics of North America 24, no. 2 (2004): 215–23.

Sheikh, J. "Advances in the treatment of chronic urticaria." Immunology and Allergy Clinics of North America 24, no. 2 (2004): 317–34.

ORGANIZATIONS

American Academy of Dermatology. 930 N. Meacham Road, PO Box 4014, Schaumburg, IL 60168–4014. Web site: http://www.aad.org/.

American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007–1098. Web site: http://www.aap.org/.

WEB SITES

"Hives." MedlinePlus. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000845.htm (accessed January 6, 2005).

"Hives (Urticaria)." San Francisco State University Student Health Service. Available online at http://www.sfsu.edu/~shs/skinclinic/urticaria.htm (accessed January 6, 2005).

"Urticaria (Hives)." American Osteopathic College of Dermatology. Available online at http://www.aocd.org/skin/dermatologic_diseases/urticaria.html (accessed January 6, 2005).

L. Fleming Fallon, Jr., MD, DrPH