Urticaria, also called hives, are red, itchy, swollen areas of the skin that can range in size and appear anywhere on the body. The blotches can migrate on body, appearing in different areas throughout the course of the reaction.
Usually, the cause of urticaria is readily identifiable—often a viral infection, or allergic reaction to drugs, food or latex. These hives can resolve spontaneously or by avoiding the allergic trigger. However, frequently, medical intervention is needed to increase comfort or prevent recurrence. Treatment with oral antihistamines is often successful, but for severe cases, steroids may be needed.
Some people have chronic urticaria which is hives that that occurs nearly daily for more than six weeks. For these individuals, scratching, pressure or stress may aggravate their hives. An allergist/ immunologist can diagnosis the problem and prescribe treatments for this bothersome condition.
Source: American Academy of Allergy, Asthma and Immunology