A hard lump in the tailbone may be caused by local infection, tumor, spinal lesions and other factors. 1. Local infection: due to the low immunity and bacterial invasion, the tailbone may be infected, and the soft tissue may be swollen locally, with reddish skin color, increased skin temperature and pressure pain, and may be combined with systemic manifestations, such as fever, chills and hyperthermia. 2. Tumor: hard lumps can be touched at the tailbone, which may be caused by local tumors, such as sacrococcygeal chordoma, liposarcoma, smooth muscle sarcoma, chondrosarcoma and Ewing’s sarcoma, etc. The local lumps can be progressively enlarged, and the pain will be aggravated with the increase of pain, and it is necessary to consult a doctor for pathological biopsy and other means to confirm the diagnosis in time. 3. Spinal lesions: the vertebral plates on both sides of the spine and lumbosacral vertebral plates are not completely healed, which can cause the tissues in the spinal canal to protrude to the outside under the action of external force or other causes, and a hard lump can be formed at the tailbone. When there is a hard lump in the tailbone, you should consult a doctor in time and take appropriate treatment after the condition is clarified by a specialist to avoid delaying the condition.