Red nevus can be caused by physiological factors, allergic purpura, liver function abnormality and so on. 1. Physiological factors: some people who work in high temperature for a long time will cause capillary expansion of subcutaneous dermal papillary layer, and red nevus will appear on the body, which is a normal physiological phenomenon. Some pregnant women will cause the estrogen level to rise, the liver metabolism decreases, resulting in the appearance of red nevus, do not need to do special treatment, wait until the baby is born will disappear. 2. Anaphylactic purpura: It is a kind of small-vessel allergic reaction disease. Red blood spots of the size of a pinhead or a soybean will appear on the skin lesions, similar to the performance of a red nevus, which will gradually merge into a piece, and will usually subside automatically in 1~2 weeks. 3. Abnormal liver function: Due to the metabolic problem of liver function, the inactivation ability of liver to estrogen will be reduced, and then the spider nevus will appear. Spider nevus has a blood-red color, which can be seen as red blood nevus on the body. All in all, when red nevus appears on the body and continues to be unrelieved, it is recommended to consult a doctor in time to find out the cause and treat the symptoms.