Acne is likely caused by testosterone (there can be many other factors such as genetic predisposition, dry skin causing secretion of sebum, among others). This is why younger men get it most often. Back acne is treated the same way as acne on your face. There are antibiotics you can be prescribed. The most common ones used are erythromycin, tetracycline, minocycline, and doxycycline . If it is very severe you might be able to get get on Isotretinoin(Accutane), but you will have to have tried antibiotics beforehand(unless you have a free prescribing doc). There are topicals you can use as well such as benzoyl peroxide and salicylic acid if you can get someone to rub it on. I have had acne my whole life, but do not have it anymore (im 25), and I am currently a physician assistant student so I have a decent understanding of acne. If you have any questions just PM me.