There are many reasons for long black vertical lines on the nails, such as physiological phenomenon, nail moles, nail malnutrition, and bruises under the nails. 1. Physiological phenomenon: long black vertical lines on nails may belong to congenital heredity, usually parents, elders may have the phenomenon, so they get heredity caused, usually not accompanied by other symptoms. 2. Nail nevus: long black vertical lines on the nails may also belong to the nail nevus, the main typical performance for the nail black line, usually no other discomfort symptoms. 3. Nail malnutrition: If the patient is deficient in trace elements, vitamins, etc., because the nails can not get enough nutrients, there may also be long black vertical lines on the nails. 4. Bruising under the nail: the nail is traumatized, resulting in bleeding under the nail, which gradually forms a strip of pigmentation. This can also lead to long black vertical lines on the nails. There are many reasons for long black vertical lines on the nails, and it is recommended to go to the hospital in time to improve the examination and take standardized treatment according to the doctor’s instructions, so as not to ignore the symptoms and take them lightly.