Home Cosmetic Science Talk Formulating Low pH enough to inhibit mold growth?

  • Low pH enough to inhibit mold growth?

    Posted by zink on April 14, 2020 at 3:50 pm

    Wondering if you could increase the glycolic acid content of a formula to inhibit mold growth, also can you go below pH 3 if the strength of the acid is still low? E.g. low concentration, but with no buffers used.

    zink replied 3 years, 11 months ago 3 Members · 5 Replies
  • 5 Replies
  • zink

    Member
    April 20, 2020 at 7:29 am

    bump

  • oldperry

    Member
    April 20, 2020 at 1:36 pm

    Mold growth can happen at pH as low as 3.5 so if you go lower, that should inhibit mold growth.

    However, the pKa of Glycolic acid is 3.8 so I don’t think you will be able to get a pH much lower than that without some buffers. I’m not positive though as my knowledge of acid/base chemistry is a bit rusty.

  • pharma

    Member
    April 21, 2020 at 7:27 pm
    A 1 M solution of pure glycolic acid has, due to the lower pKa, a pH of (estimating/guessing here) less than 2 because acetic acid has about 2.5.
    pKa only matters if there is a buffer present or a salt used but not in case of a pure acid. Given that you intend using diluted glycolic acid, the pH might slightly differ. You easily get down to a pH where nothing (at least nothing you commonly encounter in human inhabitable surroundings) can grow but then again, your skin might not be very happy… unless you use a strong enough dilution to get something which can be ‘buffered away’ by whatever is on your skin (many constituents of NMF buffer nicely).
  • oldperry

    Member
    April 21, 2020 at 8:23 pm

    @Pharma - yeah, I couldn’t find a pH for “pure glycolic acid” in any of my sources.  hmmm.

  • zink

    Member
    April 22, 2020 at 8:21 am

    In my experience as long as you use a low percentage of acid, low pH is not a problem, like Pharma says, it’s buffered away by the skin.

    Even though the acid is a solution easily loses protons, there isn’t that many of them.

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