I am currently using the apple cider vinegar method to get rid of some newer hyperpigmentation on my chest and face and it has helped a lot so far. But i was wondering if anyone knew if apple cider vinegar works on old hyperpigmentation. The old ones have been on my back for a few years now and they lightened up a little after I did two 12.5% TCA peels, but they're still noticeable. Does anyone know if ACV works on old hyperpigmentation? Also since it's the skin on my back and that skin is tougher than my face and chest how much should I dilute it? Thanks for any help.