Hives are raised, often itchy, red welts on the surface of the skin. They are usually an allergic reaction to food or medicine.

Urticaria

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.