A small hard bag on the right side of the back of the head without pain may be caused by sebaceous cysts, subcutaneous fibromas, lipomas and other diseases. 1. Sebaceous cysts: there will be hard bumps under the surface of the skin, and there will also be local symptoms of redness or swelling of the skin. 2. Subcutaneous fibroma: may be related to trauma, local inflammatory stimulation. It manifests as a hard lump, difficult to push, fixed position. If it presses on nerves and blood vessels, surgery can be performed to remove it. 3. Lipoma: benign tumor with proliferation of fat cells, which can occur in the head, manifested as painless small hard lumps, generally without special treatment, if the tumor is too large or compressed to the surrounding tissues, it can be surgically excised. If the tumor is too big or presses into the surrounding tissues, it can be removed by surgery. Small hard bags in the back of the head may also be caused by other reasons, and it is recommended to consult a doctor in time to clarify the cause and then carry out corresponding treatment under the guidance of the doctor.