Urticarial lesions itch, have a central white wheal that is elevated, and are surrounded by an erythematous halo. The lesions are typically rounded and circumscribed. Characteristically, hives should blanch with pressure; they generally resolve within 24 hours, leaving no residual change to the skin. The redness, which is augmented by local neural reflexes, is due to dilated blood vessels in superficial layers of the skin; the wheal is due to leakage of these vessels as fluid extravasates and compresses the vessels beneath it so that the central area appears clear.

 

Swelling of deeper layers of the skin, angioedema, commonly accompanies urticaria (click for picture). This swelling often results from the same inflammatory processes that cause hives. The redness that is seen surrounding superficial lesions is not observed, though the swelling is readily appreciated. Angioedema generally occurs on the extremities and digits as well as areas of the head, neck, face, and in men, genitalia. It is often described as being painful or burning.