A hard bag on the back that hurts when pressed needs to be treated according to the cause. Common causes include boils and sebaceous cysts, which are usually treated with medication and surgery. 1. Boils: When the skin on the back is scratched or abraded, bacteria can easily invade the skin from the mouth of the hair follicle, thus triggering boils, which are manifested as one or more red, hemispherical and painful hard packs on the surface of the skin. Patients can use local topical mupirocin ointment, ichthyol ointment, etc., and severe symptoms can be combined with oral antibiotic drugs, such as amoxicillin capsules, tetracycline capsules. 2. Sebaceous cysts: Sebaceous cysts are caused by the blockage of sebaceous gland ducts in the skin, and are common in the face, back, buttocks, etc. They appear as round, medium-hard bumps on the surface of the skin, and usually have no conscious symptoms, and when secondary bacterial infections occur, they will appear red, swollen, pus-filled, painful, and so on. Sebaceous cysts inflammation and infection can be oral cefixime capsules, amoxicillin capsules and other antibiotics, local topical erythromycin ointment, mupirocin ointment and so on to carry out the treatment, to be inflammation subsides, can be used to surgical excision of the method of treatment. All of the above drugs have adverse reactions and are recommended to be used under the guidance of a doctor. A hard bag on the back will be painful when pressed, there may be other causes, it is recommended to go to the hospital in time to improve the examination, to clarify the cause of the disease to give targeted treatment.