Hives is an allergic skin reaction causing localized redness, swelling, and itching.
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.
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
- 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.
Hives are easily diagnosed by visual inspection. The cause of hives is usually apparent but may require a careful medical history in some cases.
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.
Most cases of hives clear up within one to seven days without treatment, providing the cause (allergen) is found and avoided.
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.
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.
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.
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.
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American Academy of Dermatology. 930 N. Meacham Road, PO Box 4014, Schaumburg, IL 60168–4014. Web site: <www.aad.org/>.
American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007–1098. Web site: <www.aap.org/>.
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L. Fleming Fallon, Jr., MD, DrPH