Hives, or more properly urticaria, are a type of rash characterized by pale red, raised itchy bumps. They are usually the result of an allergic reaction, either from direct contact with the skin or ingestion of food. Hives as an allergic reaction usually fade within a few weeks, and hives that last longer are usually the sign of an underlying condition, often an autoimmune condition. However, hives can also arise from friction, changes in temperature, exercise and exposure to sunlight.
Hives are caused when histamines cause fluid to leak from blood vessels. They can range from the size of a pinprick to a few inches across. Hives are generally treated with antihistamines, but steroids are occasionally used with serious or chronic cases.