Black spots on finger nails may be symptoms caused by nail trauma, nail melanoma, malnutrition and other diseases. Patients should go to the hospital in time, under the guidance of the doctor to identify the cause of the disease, symptomatic treatment. 1. Nail trauma: when the fingernail is squeezed or bumped, it will cause blood stasis under the nail, which will lead to the symptom of black spots on the fingernail. With the passage of time, the black spots caused by nail trauma can gradually subside or be discharged. 2. Nail melanoma: Nail melanoma is a primary tumor of the nail. Patients with subnail melanoma may have the symptom of black spots in the nail cover. The growth rate of subnail melanoma is fast, and patients should consult doctor in time to find out whether it is malignant or not, and undergo surgical treatment if necessary. 3. Malnutrition: malnutrition is easy to be caused when the nutrient intake of the body is insufficient. The capillaries of malnourished patients are more fragile, which can easily cause the rupture of capillaries under the nail and produce black spots. Patients with black spots on fingernails should consult the doctor in time and under the guidance of the doctor for regular treatment.