Hives medically known as urticaria, appear on the skin as wheals that are red, very itchy, smoothly elevated areas of skin often with a blanched center. They appear in varying shapes and sizes, from a few millimeters to several centimeters in diameter anywhere on the body. Hives can change size rapidly and move around, disappearing in one place and reappearing in other places, often in a matter of hours. Occasionally hives are produced by direct physical stimulation by environmental forces like heat, cold, and sunlight.
Hives affects about 20 percent of people at some time during their lives. Hives are very common, and most often their cause is elusive. What cause hives?