What Are Hives?

Picture of urticaria pigmentosa. The skin has been irritated and the resulting hives are shown.

Medically known as urticaria, hives are red, itchy, raised areas of skin that appear in varying shapes and sizes on the body, especially the torso, arms and legs. They range in size from a few millimetres to several centimetres in diameter.

Hives can be round, or they form rings or large patches. Welts, which are red lesions with a red ‘flare’ at the borders, are another manifestation of hives. Hives are produced by histamine and other compounds released from cells called mast cells, which are a normal part of skin. Histamine causes fluid to leak from the local blood vessels, leading to swelling in the skin.