Hives (urticaria) are red, itchy welts that result from a skin reaction. The welts vary in size and appear and fade repeatedly as the reaction runs its course.
Hives are characterized as itchy red, raised welts (also known as wheals) on the skin's surface that can spread or join together and form larger areas of raised lesions. They are generally triggered by exposure to an allergen or chemical irritant. They tend to appear suddenly and often disappear equally as suddenly.
Hives lasting more than six weeks are known as chronic urticaria or, if there is swelling below the surface of the skin, angioedema. There are no known causes of angioedema, but it can affect internal organs and therefore requires medical attention.