Nail bruising can be caused by trauma, onychomycosis and aplastic anemia. 1. trauma: if the nails are squeezed, collision and other external substances brought about by the injury, may lead to nail injury, thus appearing nail bruises. 2. Ringworm of the nail: ringworm of the nail is a disease in which the skin fungus violates the nail and leads to nail lesions. The nail plate of patients with ringworm of the nail will appear cloudy, thickening, separation and discoloration, and so on, and there may also be pain and the symptom of bleeding under the nail, which leads to bruising of the nail. The cause of the disease is mostly related to dermatophyte infection. 3. Aplastic anemia: aplastic anemia is a disease of bone marrow hematopoietic failure caused by a variety of reasons, the cause of which is mostly related to genetics, viral infections, and immune abnormalities, etc. The patient will experience progressive aggravation of anemia, infections, and bleeding, etc., and some of the patients will experience nail bruising. In addition, coagulation disorders, such as hemophilia, primary thrombocytopenic purpura and other diseases, and minor trauma, may lead to bruising under the nails. There are many causes of nail bruising, and it is recommended that the patient consult a doctor for examination to determine the cause of the disease and then treat it accordingly.