The bruising of breasts is considered to be caused by violent pinching, which can lead to the rupture of capillaries under the skin, causing subcutaneous bleeding and bruising of breasts, especially for fair-skinned women. When the coagulation mechanism in the body is impaired, the lack of coagulation factors will lead to clotting disorders, which will also cause the rupture of the capillaries under the skin, and the skin will be subjected to a slight collision, and subcutaneous bruising can occur. In addition to breast bruising, subcutaneous bleeding can also be seen on other parts of the body and requires prompt medical attention to check coagulation mechanisms. Breast bruising can also be seen as subcutaneous bruising after breast surgery, which is caused by subcutaneous blood leakage from the surgery and is quickly self-absorbing. In either case, it is recommended to go to the hospital for a detailed examination to confirm the specific cause and to avoid more serious complications with timely and symptomatic treatment.