I have a foaming sugar scrub with, according to my calculations, 3.5%-4% water (mostly coming from a surfactant). Now when it comes to preservatives, what would be maximum water level in % to be eligible for anhydrous product and not have preservative at all. According to USP <1112> if the water activity is under 0.91 I'm ok for bacteria and under 0.6 ok for yest and mold.
I understand that it is a high sugar content product (23%) and bacteria just loves sugar, so I'm realizing that not having a preservative at all might not fly by, but do I really need the full dose? How much preservative (say phenoxyethanol) would be substantial to take care of 3.5-4% water?
Thank you all for your help!!!