Bleeding spots or petechiae on the skin often indicate an abnormal change in hemostasis. The body’s hemostatic function is carried out by the blood vessels, platelets and clotting factors. Lesions in any one of these can lead to bleeding. Thin capillary wall: The capillary wall is very thin, with only one layer of endothelial cells, connected to each other by a layer of adhesive material. Vitamin C deficiency affects the synthesis of adhesive mass; certain infectious diseases such as epidemic hemorrhagic fever, sepsis, hypoxia and poisoning can also damage the capillary wall, increasing its permeability and the outflow of blood cells from the interstices of the wall, and can also increase the capillary brittleness and make it easy to rupture. All these conditions can lead to bleeding. The common clinical condition of allergic purpura is due to capillary allergic inflammation, which increases the permeability of the tube wall and not only has skin bleeding spots and edema, but also can involve other internal organs and organs, while abdominal pain, joint pain and hematuria, proteinuria, etc. Low platelet count and functional decline can also lead to bleeding: the former is seen in aplastic anemia, acute leukemia and primary thrombocytopenic purpura; the latter is seen in uremia, hepatic sclerosis and other diseases. Coagulation factors: When small blood vessels are broken, they rely on the aggregation ability of platelets to block the wounds and stop bleeding. However, large wounds also require large blood clots formed by clotting factors in the blood in order to be plugged. Therefore, when clotting factors are lacking, the blood does not clot easily after the skin vessel ruptures and petechiae form. Since most clotting factors are synthesized in the liver and require the participation of vitamin K, they tend to bleed easily when there is a liver lesion or vitamin K deficiency. Others: diseases such as chronic nephritis and systemic lupus erythematosus often have abnormal substances that interfere with the normal coagulation process, so bleeding can also occur. As can be seen, there are many causes of bleeding, and a clear diagnosis can only be made by going to the hospital for tests such as platelet count, bleeding time and clotting time.