Hives (urticaria), involve red, itchy, swollen areas of the skin that range in size and appear anywhere on the body. They can appear suddenly, and may be the result of an allergic reaction.
Some people have chronic urticaria that occurs almost daily for months or, in some cases, years. Treatment with oral antihistamines is frequently successful, but in severe cases, steroids may be needed.
In addition to allergic reactions to medications, foods, or other substances, hives may be triggered by viral infections, temperature extremes, water, sun, and physical exercise.