Hives are raised, often itchy, red bumps (welts) on the surface of the skin. They are usually an allergic reaction to food or medicine.
When a person has an allergic reaction to a substance, his/her body releases histamine and other chemicals into the blood. This causes itching, swelling, and other symptoms. Hives are a common reaction. Persons with other allergies, such as hay fever, often get hives. When swelling or welts occur around the face, especially the lips and eyes, it is called angioedema. Swelling can also occur around the hands, feet and throat.
Many substances can trigger hives such as animal dander (especially cats), insect bites, medicines, pollens, certain food items, extreme cold or sun exposure, etc.
Itching, swelling of the surface of the skin into red- or skin-colored welts with clearly defined edges.
Wheals may get bigger, spread, and join together to form larger areas of flat, raised skin.
Wheals can also change shape, disappear, and reappear within minutes or hours.You know you have hives when you press the center of a wheal, it turns white.This is called blanching.
Source: Portal Content Team