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Hives are raised, often itchy, red welts on the surface of the skin. They are usually an allergic reaction to food or medicine.
When you have an allergic reaction to a substance, your body releases histamine and other chemicals into your bloodstream. This causes itching, swelling, and other symptoms. Hives are a common reaction, especially in people with other allergies such as hay fever.
When swelling or welts occur around the face, especially the lips and eyes, it is called angioedema. Swelling from angioedema can also occur around your hands, feet, and throat.
Many substances can trigger hives, including:
Hives may also develop as a result of:
The hives may get bigger, spread, and join together to form larger areas of flat, raised skin.
They can also change shape, disappear, and reappear within minutes or hours. A true hive comes and goes. When you press the center of one, it turns white. This is called blanching.
Your doctor can tell if you have hives by looking at your skin.
If you have a history of an allergy, then the diagnosis is even more obvious.
Occasionally, skin or blood tests are done to confirm that you had an allergic reaction and to test for the substance that caused the allergic response. A skin biopsy can confirm the diagnosis.
Treatment may not be needed if the hives are mild. They may disappear on their own. To reduce itching and swelling:
If your reaction is severe, especially if the swelling involves your throat, you may require an emergency shot of epinephrine (adrenaline) or steroids. Hives in the throat can block your airway, making it difficult to breathe.
Hives may be uncomfortable, but they generally are harmless and disappear on their own. In most cases, the exact cause of hives cannot be identified.
Call 911 or your local emergency number if you have:
Call your health care provider if the hives are severe, uncomfortable, and do not respond to self-care measures.
Habif TP, ed. Clinical Dermatology. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2009.