The hard bumps on the waist may be caused by dermatofibroma, common warts, seborrheic keratosis, and so on. 1. Dermatofibroma: Dermatofibroma is a benign tumor caused by the proliferation of fibroblasts, which can occur in all parts of the body, and if it occurs in the lower back, it may appear as hard bumps on the waist. 2. Common warts: If you feel a hard bump on the epidermis of your waist, it may be a common wart formed after a human papilloma virus infection, and this hard bump is usually characterized by a rough surface and a papillomatous appearance. 3. seborrheic keratosis: seborrheic keratosis occurs on the surface of the body, belonging to benign skin tumors, manifested as dark papules or plaques with a rough surface, which can lead to the appearance of the epidermis of the waist touching the hard bumps of the situation. Patients with hard bumps on the waist, should go to the regular hospital in time to find out the cause of the disease, under the guidance of professional doctors to give targeted treatment.