Hives are red, very itchy, swollen areas of the skin.
Hives arise suddenly and may leave quickly in 1-2 hours or can last as long as 48 hours. They often appear in clusters, with new clusters appearing as other areas clear. Physicians refer to hives as urticaria. Over one-fifth of the population has suffered an eruption of hives at some point in their lives. Hives can be caused by allergic or non-allergic mechanisms.