A piece of the back of the waist is a bulge that may be caused by lipoma, fibroma or sebaceous cyst. 1. Lipoma: Lipoma is a benign tumor caused by the proliferation of adipose tissue, which can occur in various parts of the body, and the more common one is subcutaneous lipoma. When lipoma is small, no treatment is needed. For larger ones or those affecting the appearance and function, they can be removed by surgery. 2. Fibroma: it may appear in both men and women. Fibroma is caused by the proliferation of fibrous tissues, and the surface of the tumor is wrapped with an envelope, which is very smooth and has a clear boundary. The internal components are mainly fibrous tissues and may also contain some glandular tissues. Patients are advised to remove the lump and undergo pathological examination in order to diagnose the cause and treat it. 3. Sebaceous cyst: It is a kind of sebaceous secretion retention and stagnation disease. Sebaceous cysts are common among young people, mainly manifested by blackheads and cyst infections in the lesions, and occasionally cancerous. Treatment is based on anti-infection and surgical excision. When there is a bump behind the waist, it is recommended to go to the hospital and follow the doctor’s instructions to avoid delaying the condition.