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. Hives may be triggered by viral infections, temperature extremes, water, sun and physical exercise.*
*Source: American Academy of Allergy Asthma & Immunology.