Urticaria or hives is a relatively common form of allergic reaction that causes raised red skin welts. Urticaria is also known as nettle rash or uredo. These welts can range in diameter from 5 mm (0.2 inches) or more, itch severely, and often have a pale border. Urticaria is generally caused by direct contact with an allergenic substance, or an immune response to food or some other allergen. Hives can also be caused by stress.

Pathophysiology

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The skin lesions of urticarial disease is caused by an inflammatory reaction in the skin, causing leakage from capillaries in the epidermis, resulting in an edema which persists until the interstitial fluid is absorbed into the surrounding cells.

Urticarial disease are thought to be caused by the release of histamine and other mediators of inflammation (cytokines) from cells in the skin. This process can be the result of an allergic or non-allergic reaction, differing in eliciting mechanism of histamine release.

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