A small hard nodule on the arm may be a lipoma or a sebaceous cyst. If it is a small lipoma, it is usually very soft, well-defined, painless to press, and very mobile. At this time, conservative treatment, i.e., regular follow-up, is not required for surgery. If you feel that the lipoma is affecting your appearance, you may need to have it removed surgically under local anesthesia. Generally, a small incision along the skin line is used to bluntly separate the lipoma and squeeze it out, and the wound can be closed with absorbable thread. If the mass is considered to be a sebaceous cyst, the mass is usually hard in texture. In addition, the surface of the mass has small black spots or small black heads, and the interior is tofu-like material, which is prone to secondary bacteria. After the diagnosis of sebaceous cyst is clear, surgical excision is recommended to remove the cyst and the cyst wall completely and then the wound is closed.