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, histamine and other chemicals are released into your bloodstream, causing itching, swelling, and other symptoms. Hives are a common reaction, especially in people with other allergies like 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:

• Medications
• Shellfish, fish, nuts, eggs, milk, and other foods
• Pollen
• Animal dander (especially cats)
• Insect bites

Hives may also develop from:

• Infections like mononucleosis or illness (including lupus, other autoimmune diseases, and leukemia)
• Emotional stress
• Extreme cold or sun exposure
• Excessive perspiration

• Itching
• Swelling of the surface of the skin into red- or skin-colored welts (called wheals) with clearly defined edges

The welts may enlarge, spread, and join together to form larger areas of flat, raised skin. They can also change shape, disappear, and reappear within minutes or hours. The welts tend to start suddenly and resolve quickly. When you press the center of a red welt, it blanches (turns white).

Your doctor can tell if you have hives by the appearance of your skin. If you have a history of an allergy, then the diagnosis is even more obvious. Occasionally, skin or blood tests are performed to confirm that this was an allergic reaction and to test for the substance that caused your allergic response.

Treatment may not be needed if the hives are mild. They may disappear on their own. To reduce itching and swelling:

• Avoid hot baths or showers.
• Avoid irritating the area with tight-fitting clothing.
• Apply calamine lotion.
• Take antihistamines.

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 obstruct 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.

• Anaphylaxis (airway is swollen, making breathing difficult)
• Life-threatening airway obstruction, if swelling occurs in the throat

Call 911 if you experience:

• Tightness in your throat
• Shortness of breath
• Tongue or face swelling
• Fainting
• Wheezing

Call your health care provider if the hives are severe, uncomfortable, and do not respond to self-care.

• Avoid exposure to substances that give you allergic reactions.
• Don't wear tight-fitting clothing and avoid hot baths or showers just after an episode of hives. These can both cause the hives to return.

Adkinson NF Jr. Middleton’s Allergy: Principles and Practice. 6th ed. Philadelphia, Pa: Mosby; 2003.

Behrman RE. Nelson Textbook of Pediatrics. 17th ed. Philadelphia, Pa: WB Saunders; 2004.

Habif TP. Clinical Dermatology. 4th ed. St. Louis, Mo: Mosby; 2004.