The cause of black toe nail may be due to extrusion or collision, which may lead to bleeding under the nail, and finally the formation of black bruises, or may be caused by disease factors, such as melanoma, which requires further examination at the hospital, and different treatment methods for different causes. 1, trauma: heavy objects squeeze or collision toe bruises under the nail and pain. If the bruising is light, cold compresses can be applied to the affected toe to slow down the blood circulation and reduce the bruising, which can be absorbed by itself after 3-5 months of recuperation. If the pain is severe and no signs of remission after recuperation, patients should seek medical attention, remove the toenail to extract the bruise, and actively anti-inflammatory treatment, the specific treatment plan is subject to medical advice, patients can not arbitrarily handle or medication; 2, fungal infection: that is, gray nail, patients can be admitted to the hospital fungal tests, if the results are positive to confirm the diagnosis, common treatment drugs such as itraconazole capsules, terbinafine hydrochloride tablets, amorolfine ointment, etc. Ketoconazole cream, etc. Non-pharmacological treatment, such as nail removal, laser therapy, photodynamic therapy and ion introduction therapy, etc., patients should be treated with medication under the guidance of a doctor; 3. Melanoma: It often appears as longitudinal black streaks with clear borders. Although melanoma is less common, it is more malignant and needs attention.