The skin bruises for no reason can be seen in three situations. 1, physiological capillary fragility increase, common in women, is a simple increase in capillary fragility, no special concern, no special treatment, plain eat more vitamin C-rich vegetables and fruits. 2, blood platelet reduction, platelet reduction can be seen in a variety of diseases, such as leukemia, aplastic anemia, immune thrombocytopenia, etc. 3, coagulation dysfunction, human blood is rich in coagulation factors, if there is a lack of coagulation factors can lead to bleeding skin mucosa. If there is a lack of coagulation factors, it can lead to bleeding of the skin mucosa, which can lead to subcutaneous bruising when external force is encountered and when the skin bleeding is difficult to stop during surgical puncture operations. If bruising of the skin occurs, it is recommended to go to the hospital to investigate the cause of the blood, and it is recommended to improve the blood routine and coagulation function tests.