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