Red bloody nevus may be caused by cherry angioma, allergic purpura, spider nevus and other diseases. 1. Cherry hemangioma: cherry hemangioma may be formed by proliferation and expansion of skin capillaries. Patients will have bright red papules and nodules in the local skin, which are round or ovoid in shape, and may be manifested as red blood nevus. 2. Anaphylactic purpura: The cause of anaphylactic purpura is not yet clear, and it may be caused by immune disorders, drugs, genetics and other factors. Patients will have different degrees of purpura, which may be manifested as purplish-red papules, and are usually asymptomatic. 3. Spider nevus: Spider nevus may be caused by estrogen secretion, impaired liver function and other factors. Patients will have red vascular nevus on the skin surface, which may be accompanied by jaundice, ascites, emaciation and other symptoms. There are many reasons leading to the appearance of red blood nevus in patients, so they can go to the hospital and find out the cause of the disease.