Nail melanoma and subnail bruising can be differentiated by symptoms, causes, and treatments. 1. Symptoms: Melanoma is a rare malignant disease, which is manifested by the gradual blackening of the longitudinal fissure of the nail plate, accompanied by melanomatous hyperplasia, and with the expanding of melanoma, there will be bloody or watery secretion; subnail bruise refers to the rupture of capillaries under the nail plate and bleeding, and the blood will have black spots when it dries up and be accompanied by pain. 2. Causes: Nail melanoma may be genetically determined and may be related to ultraviolet rays; subnail bruising may be caused by nail trauma, platelet lowering, fibrinogen abnormality and other diseases. 3. Treatment: Nail melanoma can be removed by surgery (finger amputation), and corresponding radiotherapy can be given after surgery; subnail bruise can be relieved by local cold compresses, and if it is caused by coagulation dysfunction, the primary disease also needs to be treated. Therefore, patients with nail melanoma and subnail bruise should go to the hospital as soon as possible to clarify the cause of the disease, and carry out standardized treatment under the guidance of doctors after diagnosis.