Tiny short black lines on the front of the nails are usually caused by nail dystrophy, subnail hemorrhage and other reasons. 1. Nail dystrophy: the occurrence of nail dystrophy is related to genetic factors, living habits, poor diet, disease causes, drug stimulation and so on. Patients may have the manifestation of nail color change. 2. Bleeding under the nail: it is mainly related to trauma to the nail. The rupture of capillaries under the nail will appear as a small short black line at the front of the nail. There may also be other causes, so it is recommended to go to the hospital in time to get a clear diagnosis and treatment.