The black vertical lines on nails are considered to be caused by physiological factors, malnutrition, and onychomycosis. 1. Physiological factors: usually related to the structural changes of the nails themselves, generally nails will appear vertical lines, children appear physiological vertical nail lines, will grow with age, gradually disappeared, the elderly appear physiological vertical nail lines, belonging to the normal aging phenomenon of the nails, if at the same time poor cleaning or contact with the coloring agent can be manifested as black vertical lines. 2. Malnutrition: when the lack of vitamin A, iron deficiency anemia, hypoproteinemia, etc., will cause nail malnutrition, resulting in black vertical nail lines, and even the occurrence of nail cracks, anti-nail and other symptoms. 3. Nail nevus: Nail nevus is usually a kind of tumor of nail mother cells, which is common in single hair, and a few patients will have multiple hairs, and it mainly manifests as the appearance of black stripes on the nail plate, which gradually widens and deepens in color. Nails appear black vertical stripes recommend patients to regular hospitals, under the diagnosis of the doctor, clear causes, targeted treatment.