About 20% of people get hives -- itchy red or skin-colored welts also known as urticaria. They’re often caused by an allergic reaction to a food or drug. Usually, they go away quickly.
For a small number of people, though, hives come back again and again, with no known cause. When new outbreaks happen almost every day for 6 weeks or more, it’s called chronic idiopathic urticaria (CIU).