Sudden growth of black moles on fingers is considered to be the cause of melanosis, pigmented nevus, melanoma, etc., which can be treated by applying medication, physical therapy, surgical excision and other methods according to the doctor’s instructions. 1. Melanosis: Melanosis is a kind of hyperpigmented skin disease, which is related to long-term exposure to ultraviolet rays, and photosensitive substances will produce certain irritation to the skin and pigmentation, leading to the sudden growth of moles on the fingers. Vitamin A acid ointment and hydroquinone cream can be applied for treatment, and the pigmentation can be improved after using the medicine. 2. Pigmented nevus: pigmented nevus is a benign skin tumor composed of nevus cells, which is related to trauma and hormone level changes, and a large amount of melanin is still deposited locally, causing the patient’s finger to suddenly grow a black nevus. It can be treated by laser and freezing. 3. Melanoma: Melanoma belongs to a kind of malignant tumor, the disease usually develops more rapidly, and the cancer cells will spread to the surrounding skin in large quantities, causing the patient’s finger to suddenly grow a black mole. Melanoma can be treated by surgical removal of melanoma, and chemotherapy is also needed after surgery. There may be other reasons for the sudden growth of moles on the fingers, so it is recommended to consult a doctor in time for treatment under the guidance of the doctor.