The acid mantle is our skin’s defense system, a very fine slightly acidic film produced in part by our outermost layer of skin (or the Stratum Corneum) where it contributes sebum (oils, waxes, esters) and sweat (water, salt). The acidity develops when the bacteria on our skin (don’t worry, this kind of bacteria is our friend, and he’s awesome!) breaks down these oils into fatty acids and glycerol. The average pH of the acid mantle of healthy skin is 5.5. Depending on your age, gender, skin type etc. this number can change.