Definition of Hives:

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

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Causes, incidence, and risk factors:

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:

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

Hives may also develop as a result of:

• Emotional stress
• Extreme cold or sun exposure
• Excessive perspiration
• Illness (including lupus, other autoimmune diseases, and leukemia
• Infections such as mononucleosis