ChU involves the formation of small wheals (pencil-rubber sized) that are typically surrounded by a larger reddened portion of skin called a flare. In most cases the skin changes occur within 2 to 20 minutes after a raise in body temperature and with the onset of sweating, generally starting with the throat and upper body. The patient often first notes itchiness or a prickliness or burning of the skin. Once the body cools back down, the wheals disappear without a trace within minutes or hours. Depending on the degree of severity of the disease, sometimes only a few wheals form on the buttocks; in serious cases the entire body can be affected. Fortunately, ChU only rarely involves serious symptoms like angioedema (deep swelling of the skin), respiratory problems, nausea, headaches or circulatory problems.