A urticarial rash is also known as hives, which is an eruption of wheals on the skin, according to WebMD. The reasons why some people get hives are unknown, but many cases are related to allergies.
Hives itch, burn and sting, according to WebMD. Any part of the body can be afflicted with hives, including the tongue and the throat. Wheals, which are swollen bumps, may be small or they may start small and enlarge. They may even join with other wheals to form plaques. They tend to persist for hours before they finally start to fade.
Hives caused by allergies come about because the chemical histamine causes blood plasma to leak out of the capillaries in the skin, says WebMD. In addition to allergies to foods, hives can be caused by exposure to sunlight, insect stings or medicines. They can be acute or chronic. Acute hives last less than six weeks, while chronic hives last more than six weeks. It is difficult to find out what causes chronic hives, but they might be the body's response to infection and disease. Chronic hives can also affect the internal organs.
Other types of hives are physical uriticaria and dermatographism, claims WebMD. In the former, the hives appear after a particular area of skin has been physically stimulated by heat, cold, sun, sweating, exercise or pressure. With dermatographism, hives appear after the skin is firmly stroked or scratched.