Hives are itchy red welts on the skin. They vary in size from a few millimeters to as large as a dinner plate. Although a bout of hives can last for a few weeks, individual hives come up and go away in 24 hours or less. New ones form as old ones disappear. Allergens, such as certain foods, medications, chemicals, insect bites or stings, animals, and pollen can cause hives, but other causes can include infections, internal illnesses, exposure to intense heat or light, exercise, stress, or scratching the skin.
Although hives often go away on their own, in severe cases, called angioedema, throat swelling can occur, making it difficult to breath or swallow. If this happens, it is critical that you seek emergency medical care immediately. Treatment for hives often involves stopping contact with a culprit allergen, if one is causing the hives. For itch, antihistamines or topical medications may be prescribed.