What are hives?Hives are raised welts that can appear anywhere on your skin and are usually itchy. The medical term for hives is urticaria. Hives are usually red or skin-colored, and they vary in size from a pea to a dinner plate. Look for a reddish halo surrounding the border of these itchy skin plaques. Hives are most often triggered by the release of histamines in the skin, which causes localized swelling, burning and itching. Hives can result from allergic reactions or may be due to many other conditions. Individual welts or spots usually will not last more than a day, though new hives may appear, and the general condition can last for weeks depending on the cause. Many hives may join together to form a very large welt. Scratching, compressing, heating or cooling hives excessively can worsen them. Though itchy and uncomfortable, hives are usually self-limiting and disappear on their own. In rare circumstances, hives can be a sign of a more serious allergic reaction wherein similar changes occur within the mouth, the airways, and the digestive tracts. A visit to your health care professional may help to determine what triggered your hives, though the exact cause is usually difficult to determine. Seek immediate medical care (call 911) for serious symptoms, such as difficulty breathing or swelling of the tongue. These symptoms can be a sign of a serious allergic reaction known as anaphylaxis, which can be life threatening if not treated immediately. Seek prompt medical care if you are being treated for hives but mild symptoms recur or are persistent.