The blackening of the root of the toenail may be caused by onychomycosis, toe trauma, onychomycosis and other diseases, which can be treated by applying medication, oral medication and surgery as prescribed by the doctor. 1. Onychomycosis: Onychomycosis is usually caused by dermatophytes invading the nail plate, which can easily lead to thickening and blackening of the nails. It can be treated by applying antifungal medications such as amorolfin rub. 2. Toe trauma: if the patient’s toes have been pinched or smashed, it will easily lead to bruising in the nail area, and the bruises will gather for a long time and the nails will be blackened. Generally no special treatment is needed, and it can gradually absorb and subside by itself. 3. Inguinitis: Inguinitis may be caused by bacterial infection, in the repeated infection of the inflammation will stimulate the toes will easily lead to the toes skin redness, swelling and pus, will also lead to thickening of the nail plate, blackening of the symptoms. Mupirocin ointment, fusidic acid cream and other drugs can be used for treatment, for serious patients can also be carried out nail extraction or abscess drainage treatment. The blackening of the root of the toenail may also be caused by a disease such as onychomycosis, and the patient needs to consult a doctor for examination and treatment according to the cause of the disease.