Black vertical lines on finger nails may be caused by onychomatous nevus or subnail melanoma, it is recommended to consult a doctor in time to find out the cause of the disease. 1. Nevus of Onychomycosis: Nevus of Onychomycosis is a kind of pigment cell nevus in the nail area, the pigment produced by the nevus cells is deposited in the newborn nail plate, so the symptom of black vertical lines on fingernails can appear, except for the black nail lines that can be seen on the nails, usually there is no other discomforts, and if the shape of the vertical lines is stable and does not have expansion, it is usually benign, and there is no need to have any special treatments. 2. Subnail melanoma: Subnail melanoma is a disease caused by malignant proliferation of melanocytes located in the nail bed, which can also lead to the symptom of black vertical lines on fingernails. If the pigmented bands on the nails become wider and irregular, and the skin around the nails also has pigmentation, then the patient should be highly alert, and should undergo surgical excision as early as possible and complete histopathological examination. The appearance of black vertical lines on the nail is recommended to seek medical treatment as soon as possible, to the regular hospital to find out the cause, so as not to delay the condition.