Small red vertical lines on the nails may be caused by trauma, nail fungus disease and other diseases. 1. Trauma: red vertical lines on the nails may be caused by trauma, the capillaries under the nails may be damaged or ruptured due to trauma, which will lead to the appearance of red vertical lines. 2. Nail fungus disease: Nail fungus disease is usually caused by dermatophyte infection, and may also be caused by tinea infection and other factors. The patient’s nail plate will appear cloudy, discoloration, atrophy, uneven surface, etc., there will also be pain and bleeding under the nail, etc., which may lead to the appearance of small red vertical lines on the nail. There are many reasons for red vertical lines on the nails, and it is recommended that patients seek medical examination to clarify the cause of the disease and cooperate with doctors to standardize treatment.