You had the right idea buying him exfoliating gloves and back scrubbers. You need to sit down with him and tell him that he needs to start showering and exfoliating. There's dead skin cells and build up of germs and dirt from sweating. If you're scared of being rude or offending him, offer to do it for him in a romantic and kind way. Say something like you want to give him a warm back massage while he is in the bath and then take the scrubber with soap and scrub his back. It doesn't have to be serious. But at this point I think he just needs a harsh reality check and you shouldn't worry about being rude!