Big toe nail cover under the purple-black considerations are caused by trauma, may also be the emergence of nail dystrophy, nail ringworm and other diseases, need to consult a doctor in time to check the treatment, the treatment method includes drugs and surgical treatment and so on. 1. trauma: if the nails are hit by external forces, it may lead to blood pooling in the nails, so this symptom will appear, generally do not need too much treatment, usually will gradually recover. 2. Nail dystrophy: clinically, nail dystrophy may lead to abnormal nail morphology and structure, it is easier to appear under the nail cover purple-black symptoms, but also may lead to thinning and roughness of the nail plate. It can be treated with medication, such as prednisone, dexamethasone, etc. In severe cases, surgical treatment may be needed to remove the diseased nails. 3. Ringworm of the nails: patients with ringworm of the nails after the fungus invades the nail plate, this situation can be treated with drugs such as amorphophallus application, cyclic acetone ammonia nail coating and so on. Usually need to pay attention to observe the big toe nail recovery, if there is any abnormality need to consult a doctor in time, the above drugs need to be used under the guidance of a doctor.