Hives (urticaria) - close-up
![Hives (urticaria) - close-up](/TransAdam/doc/graphics/images/en/1651.jpg)
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.
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