Hives usually appear suddenly and go away on their own in a matter of days, hours, or even minutes.
Chronic hives, however, can last for six weeks or more.
Foods (commonly eggs, shellfish, nuts, berries, dyes, or other additives) and drugs (any drug can touch off an allergic reaction, although allergies to penicillin, sulfa, and aspirin are especially common) are common causes of this outbreak.