A lump inside the waist may be caused by epidermoid cyst, dermatofibroma, lipoma and other diseases. 1. Epidermoid cysts: the cause is not clear, patients may appear round raised nodules under the skin, visible in any part of the body. 2. Dermatofibroma: the cause is not clear. Patients may develop round firm nodules, usually single, usually dark brownish brown-red, etc., mostly in the limbs, but also in other parts of the body. 3. Lipoma: it is a common benign soft tissue tumor, which may be related to heredity, chronic inflammation and other factors. Patients will have one or more localized lumps, and usually lipomas are softer in texture. If there is a lump inside the waist, it is recommended to go to the regular hospital to consult the doctor for examination and clarify the cause of the disease.