MedlinePlus Medical Encyclopedia: Hives (urticaria)

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Hives (urticaria) - close-up

Hives develop when histamine is released into the small blood vessels (capillaries). The capillaries dilate which causes a welt, and fluid oozes into the surrounding tissue, causing swelling. Histamine also causes intense itching.

Update Date: 10/23/2006

Updated by: Kevin Berman, MD, PhD, Associate, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network.

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