Hives, also called urticaria, is a skin reaction characterized by pale, slightly elevated swellings (wheals) that are surrounded by a red area and have clearly defined borders. Angioedema is swelling of larger areas of tissue under the skin, sometimes affecting the face and throat.

• Common triggers include insect bites or stings and foods such as eggs, shellfish, peanuts, and nuts.
• Hives may itch, and angioedema may involve swelling in the face, throat, and airways.
• Seeing a doctor is particularly important when insect bites or stings trigger a reaction.
• Antihistamines can relieve mild symptoms, but if angioedema makes swallowing or breathing difficult, prompt emergency treatment is needed.

Hives and angioedema, which may occur together, can be severe. Common triggers are drugs, insect stings or bites, allergy injections (allergen immunotherapy), and certain foods—particularly eggs, fish, shellfish, nuts, and fruits. Eating even a tiny amount of some foods can suddenly result in hives or angioedema. But with other foods (such as strawberries), these reactions occur only after a large amount is eaten. Also, hives sometimes follow viral infections such as hepatitis, infectious mononucleosis, and German measles.

Hives

Hives or angioedema can be chronic, recurring over weeks or months. In most cases, no specific cause is identified. The cause may be habitual, unintentional intake of a substance, such as penicillin in milk or a preservative or dye in foods. Hives often occur in people with an autoimmune thyroid disorder. Use of certain drugs, such as aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs—see Pain: Nonsteroidal Anti-Inflammatory Drugs), can also cause chronic hives or angioedema. Chronic angioedema that occurs without hives may be hereditary angioedema.

Symptoms

Hives usually begin with itching. Then wheals quickly develop. The wheals usually remain small (less than ½ inch across). Wheals that are larger (up to 4 inches across) may look like rings of redness with a pale center. Typically, crops of hives come and go. One spot may remain for several hours, then disappear, and later, another may appear elsewhere. After the hive disappears, the skin usually looks completely normal.

Angioedema may affect part or all of the hands, feet, eyelids, tongue, lips, or genitals. Sometimes the membranes lining the mouth, throat, and airways swell, making breathing difficult.

Diagnosis

The cause is often obvious, and tests are seldom needed because the reactions usually resolve and do not recur. In children, when hives appear suddenly, disappear quickly, and do not recur, an examination by a doctor is usually unnecessary because the cause is usually a viral infection.

If the cause is a bee sting, people should see a doctor. Then they can obtain advice about treatment if another bee sting occurs. When angioedema or hives recur without an obvious cause, an examination by a doctor is recommended.

Treatment

Usually, if hives appear suddenly, they subside without any treatment within days and sometimes within minutes. If the cause is obvious, people should avoid it if possible. If the cause is not obvious, people should stop taking all nonessential drugs until the hives subside.

For hives and mild angioedema, taking antihistamines partially relieves the itching and reduces the swelling. Corticosteroids, taken by mouth, are prescribed only for severe symptoms when all other treatments are ineffective, and they are given for as short a time as possible. When taken by mouth for more than 3 to 4 weeks, they have many, sometimes serious side effects (see Joint Disorders: Corticosteroids: Uses and Side Effects). Corticosteroid creams do not help.

In about half of the people with chronic hives, the hives disappear without treatment within 2 years. For some adults, the antidepressant doxepin, which is also a potent antihistamine, helps relieve chronic hives.

If severe angioedema results in difficulty swallowing or breathing or in collapse, prompt emergency treatment is necessary. People who have these reactions should always carry a self-injecting syringe of epinephrine and antihistamine tablets to be used immediately if a reaction occurs. After a severe allergic reaction, such people should go to the hospital emergency department, where they can be checked and treated as needed.

Hereditary Angioedema: Not an Allergy Hereditary angioedema looks much like the angioedema of an allergic reaction. However, the cause is different. Hereditary angioedema is a genetic disorder due to a deficiency or malfunction of C1 inhibitor. C1 inhibitor is part of the complement system, which is part of the immune system. In this disorder, an injury, a viral infection, or stress (such as that due to anticipating a dental or surgical procedure) may trigger attacks of swelling (angioedema). Areas of the skin and tissue under the skin may swell, as may the membranes lining the mouth, throat, windpipe, and digestive tract. Typically, the swollen areas are painful, not itchy. Hives do not appear. Nausea, vomiting, and cramps are common. Swelling in the windpipe can interfere with breathing. Diagnosis and Treatment Doctors diagnose the disorder by measuring C1 inhibitor levels or activity in a sample of blood. The drug aminocaproic acid can sometimes relieve the swelling. Epinephrine, antihistamines, and corticosteroids are often given, although there is no proof that these drugs are effective. If a sudden attack interferes with breathing, the airway must be opened—for example, by inserting a breathing tube in the windpipe. Certain treatments may help prevent subsequent attacks. For example, before a dental or surgical procedure, people with hereditary angioedema may be given a transfusion of fresh plasma to increase levels of C1 inhibitor in the blood. However, there are concerns that this treatment could trigger an attack. For long-term prevention, anabolic steroids (androgens) taken by mouth, such as stanozolol or danazol, can stimulate the body to produce more C1 inhibitor. Because these drugs can have masculinizing side effects, the dose is reduced as soon and as much as possible when these drugs are given to women.

Last full review/revision September 2008 by Peter J. Delves, PhD