Black vertical lines on the middle finger are mostly considered to be related to nevus of the nail, fungal infection, trauma and other factors. 1. Nail nevus: the cause of this disease is still unclear. Generally do not need special treatment, pay attention to observe whether accompanied by black vertical line thickening, pain and other symptoms, if there is such a tendency should go to the hospital for examination in a timely manner, to exclude malignant lesions. 2. Fungal infections: Fungal infections such as gray nails can be manifested by black vertical lines. It is suggested that patients should be diagnosed and treated as early as possible, so as not to cause inguinitis and other diseases and aggravate the condition. 3. Trauma: blood vessels rupture due to external impact, extrusion, etc., resulting in subnail hemorrhage, blood pooling in the local area, mostly manifested as nail bruising or black vertical lines. It is recommended that patients should consult a doctor in time if they have any uncomfortable symptoms, and choose the appropriate treatment plan under the guidance of the doctor.