Thumb with horizontal lines and depressions need to be treated according to the specific causes, such as trauma, nail dystrophy, onychomycosis, etc. After clear diagnosis, choose general treatment or medication. 1. Trauma: The nail itself is relatively fragile, and it is easy for the nail to develop horizontal lines and depressions due to trauma. Therefore, patients need to protect their nails to avoid nail damage. Nail damage caused by trauma can usually fade with nail growth, so no special treatment is needed. 2. Nail malnutrition: Lack of essential vitamins and trace elements can also lead to nail growth restriction, which can also lead to the phenomenon of horizontal lines and depression in the thumb. Nutrition should be strengthened, balanced diet, and supplemented with multivitamins if necessary. 3. Nail groove inflammation: Nail groove inflammation can also cause the thumb to have horizontal lines of depression, you can follow the doctor’s instructions to use antibiotic ointment, such as erythromycin ointment, compound polymyxin B ointment, and so on. If the symptoms are severe, the nail may even need to be removed. There are many reasons for the depression of the thumb, it is recommended that the patient go to the hospital in time to complete the examination, the above drugs need to be applied under the guidance of the doctor, do not use indiscriminately, so as not to lead to adverse consequences.