Purple blood spots on the body, if they occur by chance and the area of the blood spots is small, and the number of blood spots is small, this situation may be due to accidental impact or extrusion caused by capillary rupture bleeding, generally do not need to carry out further examination. However, if the purple small blood spots are larger in size and denser, this situation is highly suspicious of purpura. Purpura is commonly found in two ways: one is allergic purpura; the other is thrombocytopenic purpura, both of which are the cause of the purple small blood spots, but their pathogenesis is different. Allergic purpura is caused by taking certain drugs or infections, which leads to an inflammatory reaction of the blood vessels, so there will be small blood vessel rupture causing bleeding. Thrombocytopenic purpura is caused by a decrease in the number of platelets, which is usually accompanied by nosebleeds, bleeding gums or blood in the urine or stool.