Hives (Urticaria)

What Is It?

Hives, also called urticaria, are rounded or oval bumps (swellings) on the skin that often are itchy. Sometimes they are red, but they don't have to be. Hives happen when the cells in the skin called mast cells release histamine, a chemical that causes tiny blood vessels (capillaries) to leak fluid. When this leaking fluid accumulates in the skin, it forms the small swellings that we recognize as hives.

When people get hives, they often think it is an allergic reaction. But hives can be triggered by physical factors such as heat, cold, exercise, sunlight, stress, sustained pressure on a skin area (such as from a belt or shoulder strap), a sudden increase in body temperature (from a fever or a hot bath or shower) or from an irritating chemical, cosmetic or soap applied to the skin. Hives also can be one symptom of a whole-body (systemic) allergic reaction to something that was:

• Inhaled — Pollens, animal dander, molds
• Injected — Insect stings or bites, especially bee stings, or injected medication
• Ingested — Foods (tree nuts; fish and shellfish; dairy products; legumes, especially peanuts), food additives, medications such as penicillin or aspirin

Hives probably affect about 20 percent of people in the United States at some time in life, with the greatest number of episodes occurring in people aged 20 to 30. In rare cases, allergic reactions that trigger hives set off a chain reaction throughout the body, resulting in a life-threatening condition called anaphylaxis. Sometimes, hives last for six weeks or more, a condition called chronic (or idiopathic) urticaria. Often, no cause is found for this chronic condition, and it usually goes away on its own after several weeks.

Symptoms

Hives appear as raised whitish or flesh-colored bumps on the skin, sometimes surrounded by a red blotch. Typically round or oval, hives often itch. Hives vary in size, and some may blend to form larger areas of swelling. Hives can affect skin on any area of the body, but appear most often on the arms and legs. Most individual hives fade quickly, but new crops may appear every 24 to 72 hours if the person continues to be exposed to the environment or substance that triggered the hives.

If hives are an early sign of a whole-body reaction, other symptoms to look for include swelling of the tongue, lips or face; wheezing; dizziness; chest tightness; and breathing difficulties. If these symptoms occur, get immediate medical attention. You could be developing anaphylaxis, a life-threatening condition.

Diagnosis