Commonly known as hives, urticaria is one of the most common dermatological conditions seen by allergists. Urticaria is not just an allergic disease, however. It can be caused by metabolic diseases, medications, infectious diseases, autoimmune disease, or physical sensitivity. Traditional allergies to foods or medications as well as viral illness are frequent causes of acute urticaria which usually lasts only a few hours but may last up to 6 weeks. Chronic urticaria (lasting more than 6 weeks) is more complex, given the vast number of potential triggers. Symptoms include sudden onset; initial itching; then swelling of the surface of the skin into red or skin-colored welts (wheals) with clearly defined edges; welts turn white on touching; new welts develop when the skin is scratched; usually disappear within minutes or hours. Welts enlarge, change shape, spread or join together to form large flat raised areas.