A bag on the back that hurts when you touch it may be folliculitis, boils, acne, etc. It needs to be treated with appropriate medication, depending on the cause. 1. Folliculitis:This disease is mainly caused by bacterial and fungal infections. For the treatment of mild symptoms, topical antibiotics, such as mupirocin ointment, fusidic acid ointment, etc.; if there are fungal infections, you also need to use antifungal drugs, such as ketoconazole, terbinafine, etc.; stubborn recurrence of the need for oral antibiotic treatment, such as minocycline, doxycycline, etc.. 2. Boils:This disease is mostly caused by Staphylococcus aureus infection. If the disease is mild, it can be treated with topical antibacterial drugs, such as mupirocin ointment, compound neomycin ointment, etc. If the effect of local treatment is not good, it can be treated with oral antibiotics, such as ceftriaxone, levofloxacin, etc. If the disease is secondary to sepsis, it can be treated with oral antibiotics or intravenous antibiotics, such as ceftriaxone, etc. Bacterial cultures and surgical treatments are needed according to the condition. 3. Acne:When there is inflammation and infection, there will be tenderness. Topical antibacterial treatment, such as clindamycin, erythromycin, etc.; can also be used topically azelaic acid, inhibit the growth of germs, reduce the inflammatory response; moderate-to-severe acne, oral antibacterial treatment, such as roxithromycin, minocycline, etc.; severe acne, oral isotretinoin treatment, but there are teratogenic side effects, pregnant women and women of childbearing age is prohibited. It is recommended that patients go to regular hospitals, follow the doctor’s instructions for a clear diagnosis and reasonable treatment. When using medication, do not blindly self-medication, but strictly follow the doctor’s instructions.