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What
percentage of free acid is needed for salicylic acid to be effective against
acne? If a product containing 2 % salicylic acid has a pH of 3, then only 0.97 %
of it will be in its free acid form. That seems to be an extremely low number, especially
when learning that only the uncharged form can be absorbed through the skin. I haven’t been able to find any specific answers on google scholar.
Cheers!To be honest, I have no idea. (I don’t have much experience working on acne drugs.) My understanding is that the monograph only specifies concentration, not pH.
You might get a better answer over at Chemists Corner as they have a similar discussion thread (http://chemistscorner.com/cosmeticsciencetalk/discussion/916/labeling-products-with-salicylic-acid)There’s also a great free acid calculator from Lab Muffin that you might find helpful. http://www.labmuffin.com/2016/06/free-acid-calculator-for-exfoliants-at-specific-ph-levels/
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