How are wheals (papules) of urticaria present?

The skin swelling seen in urticaria is due to the release of histamine from mast cells and basophils in the skin, which causes small blood vessels to leak The wheal (papule) can be a few millimeters or several centimeters in diameter, colored white or red, often surrounded by a red flare, and frequently itchy Each wheal may last a few minutes or several hours and may change shape. Wheal may be round, or form rings, a map-like pattern or giant patches