The hard lumps on the buttocks where the injections were made have been there for years, which are usually caused by local tissue fibrosis and local scarring reaction. Local tissue fibrosis: local tissue fibrosis generally refers to the local fibrosis that occurs after the healing of various diseases, usually because of connective tissue metabolic abnormalities, focal fibrotic lesions and other reasons. Patients may experience hard lumps in the buttocks after the local inflammation caused by multiple injections and the tissue fibrosis after subsiding. Local scarring reaction: injections can cause damage to the skin and subcutaneous tissue of the buttocks, and hard lumps may appear when scarring is formed after healing. Patients should identify the cause of the disease under the guidance of the doctor and dispose of it according to the doctor’s instructions.