Hives, also called “urticaria,” is a type of skin rash that appears as a red, raised welt ranging in size from half an inch to 2 or 3 inches in diameter. Most of the time, hives are intensely itchy but occasionally there can be a burning quality. Typically, an individual hive lesion will last anywhere between an hour up to 12 hours and will resolve without any residual mark or discoloration. When hives last longer than 24 hours, are painful, and leave behind an area of bruising, more serious conditions should be suspected, such as vasculitis (inflammation of the blood vessels).
Hives are caused by the release of histamine and possibly other chemicals, such as leukotrienes, into the superficial skin. These chemicals lead to dilation of blood vessels, which present as swelling in the skin, and stimulation of nerve endings, which causes itching. When this same type of swelling occurs in a deeper level of the skin, the appearance of small, individual hives is lost and the involved area will appear more diffusely swollen. This manifestation is referred to as angioedema and most often occurs in parts of the body where the skin is more loosely attached to the underlying connective tissue, such as around the mouth and eyes. Because angioedema occurs at a deeper level of the skin, this type of swelling may take longer to resolve than hives.