Hard lumps growing inside the flesh on the waist may be caused by lumbar lymphangitis, sebaceous cyst, lipoma, lymphoma and so on. 1. Lumbar lymphangitis: if the patient has hard lumps inside the flesh on the waist, it may be caused by lumbar lymphangitis, mainly due to the fact that lumbar lymphangitis is easy to damage lumbar tissues, resulting in the patient having the symptoms of localized swelling and hard lumps. 2. Sebaceous cysts: due to the obstruction of sebaceous gland excretory ducts, the contents secreted by the sebaceous gland cystic epithelium gradually increase and swell, resulting in the formation of retention cysts, leading to hard lumps inside the flesh on the waist of the patient. 3. Lipoma: the etiology is not clear, and it is a subcutaneous nodule that can be touched. 4. Lymphoma: hard lumps growing inside the flesh on the waist of patients may be caused by lymphoma, which mainly manifests as painless lymph node enlargement, fever, night sweating, emaciation and other systemic symptoms. It is recommended that patients go to the regular hospital in time, under the diagnosis of the doctor, according to the patient’s condition for targeted treatment, to develop good habits, appropriate exercise, to promote the recovery of the disease.