Common causes of purpura include blood system disorders, allergies, medications, infections and hormonal abnormalities in the body. There are many common causes of purpura: 1. Blood system diseases: such as leukemia, primary immune thrombocytopenia, aplastic anemia, etc., will appear thrombocytopenia, which leads to skin purpura and so on. 2. Allergy: due to the body’s allergy to certain substances, the allergic substances into the body caused by increased permeability and fragility of the capillary wall, which can lead to purpura. 3. Drugs: some drugs such as ibuprofen, sulfonamide, etc., orally into the body to cause damage to small blood vessels, weakening the supportive tissues around the blood vessels and interfere with the function of platelets so that the blood into the subcutaneous caused by the appearance of skin purpura. 4. Infection: some bacteria, viruses, rickettsiae and protozoa infections directly damage the endothelial cells, or increase the permeability of the capillaries, may also make the capillaries bacterial embolism, resulting in purpura. 5. Hormones in the body: some young women due to abnormal hormone secretion in the body, may have an impact on blood vessels and surrounding tissues, spontaneous or minor trauma can also appear after the lower extremity skin purpura. If you find that you have purpura, you should go to the hospital in time, and the doctor will determine the specific cause of the disease according to the symptoms, signs and auxiliary examination, and give the correct treatment for the cause of the disease in a timely manner.