The presence of black vertical lines on the fingernail cover is related to a variety of factors, such as onychomycosis, subnail hemorrhage, or the presence of onychomycotic nevus, and so on. 1. Ringworm of the nails: mostly related to fungal infections, there may be white spots on the nail plate, uneven surface or black vertical lines on the nails and other symptoms. 2. Bleeding under the nail plate: mostly related to local collision or extrusion, after rupture of capillaries under the nail plate, there will be bruising or bleeding, which will be manifested as black vertical lines on the nail cover. 3. Mole of the nail: generally the black vertical lines appear from the root of the nail upward growth, the color is darker, but often not accompanied by other symptoms. There are many other factors that lead to black vertical lines on the fingernails, and after the appearance of such a situation, you should consult a doctor in a timely manner, and follow the doctor’s instructions for treatment.