The sudden appearance of a single black “mole” on the arm may be a pigmented nevus, pigmented tumor, etc. Depending on the condition, you may choose to intervene with clinical observation, medication, surgery, and other measures. 1. Pigmented nevus: Due to excessive sun exposure, medication, chemical stimulation and other factors, abnormal black pigmented nevus may appear on the surface of the skin, which is a benign lesion and usually does not require special intervention, and can be intervened by freezing, laser and other surgeries for cosmetic needs. 2. Pigmented nevus: pigmented nevus has complex causes, which can be secondary to the formation of original nevus or newly developed. Pigmented nevus is a malignant lesion of skin tissues, which requires timely intervention. It can be intervened through surgical excision and the use of chemotherapeutic drugs such as cisplatin, vincristine, paclitaxel, etc. Early intervention can improve the prognosis. The appearance of abnormal skin spots or moles, it is recommended to go to the hospital in a timely manner; the above drugs need to be used under the guidance of clinicians, unauthorized use of drugs is prohibited.