Hives medically known as urticaria, appear on the skin as wheals that are red, very itchy, smoothly elevated areas of skin often with a blanched center. They appear in varying shapes and sizes, from a few millimeters to several centimeters in diameter anywhere on the body. Hives can change size rapidly and move around, disappearing in one place and reappearing in other places, often in a matter of hours. Occasionally hives are produced by direct physical stimulation by environmental forces like heat, cold, and sunlight.
Hives affects about 20 percent of people at some time during their lives. Hives are very common, and most often their cause is elusive. What cause hives?
Hives appear when histamine and other compounds are released from cells called mast cells, which are normally found in the skin. Histamine causes fluid to leak from the local blood vessels, leading to swelling in the skin.
Allergic hives and angioedema form when, in response to histamine, blood plasma leaks out of small blood vessels in the skin. Histamine is a chemical released from specialized cells along the skin’s blood vessels. Allergic reactions, chemicals in certain foods, insect stings, sunlight exposure, or medications can all cause histamine release. It’s often impossible to find out exactly why hives have formed.
Hives are very common and are not considered contagious. Although annoying, hives usually resolve on their own over a period of weeks and are rarely medically serious. Some hives may be caused by allergies to such things as foods, infections by different organisms, medications, food coloring, preservatives and insect stings or bites, and chemicals; but in the majority of cases, no specific cause is ever found.
Although people may find it frustrating not to know what has caused their hives, maneuvers like changing diet, soap, detergent, and makeup are rarely helpful in preventing hives unless there is an excellent temporal relationship. Since hives most often are produced by an immune mechanism, the condition is not contagious. If an infectious disease were the cause of hives in a particular person then it is possible, but not likely, that an infected contact could develop hives.