Home Cosmetic Science Talk Formulating Advanced Questions Is this formulation likely self-preserving?

  • Is this formulation likely self-preserving?

    Posted by suswang8 on November 19, 2022 at 7:03 pm

    I understand that any preparation with a pH less than 4 presents a challenging environment for microbes to grow in.

    On that basis, if I have an AHA BHA toner with a pH of 3.5/3.6 and 10% ethanol, is this recipe most likely self-preserving?  

    Thank you.

    PhilGeis replied 1 year, 3 months ago 5 Members · 10 Replies
  • 10 Replies
  • markbroussard

    Member
    November 19, 2022 at 7:42 pm

    @suswang8

    It could be, by why take the chance by not adding a preservative?

  • PhilGeis

    Member
    November 20, 2022 at 11:23 am

    Unlikely.

  • suswang8

    Member
    November 20, 2022 at 7:25 pm

    @PhilGeis
    why would you say unlikely?

  • oldperry

    Member
    November 20, 2022 at 7:54 pm

    Because there are things that can grow at that pH
    Because 10% ethanol is not preserving
    Because you don’t know how much microbial exposure the product will experience 
    Because you don’t know the storage & use conditions of the product
    Because lots of reasons.

    why not just add a preservative?

  • PhilGeis

    Member
    November 20, 2022 at 8:08 pm

    As Perry said.  

  • bill_toge

    Member
    November 20, 2022 at 9:25 pm
    it depends on titratable acidity more than the pH itself; from my experience, the lowest level of acidity at which I’ve observed consistent self-preservation is around 25-30 mg KOH/g
    over several years we made dozens and dozens of batches of this product, and others with  higher acidites, and never had microbial growth in a single one
  • markbroussard

    Member
    November 21, 2022 at 12:50 am

    @suswang8

    The only way to know for certain is to test your product.  Not knowing what else is in it … I am assuming you are using a chelating agent?

  • PhilGeis

    Member
    November 21, 2022 at 12:13 pm

    Testing is not enough.  The USP51-types whatever the pass/fail are not validated to anything.
    Every recalled product passed the test.
    Folks should design a preservative system that should work and confirm it passes. 

  • bill_toge

    Member
    December 16, 2022 at 8:51 pm

    @PhilGeis that’d be ISO 11930, which is a lot more rigorous than the USP/BP challenge test

  • PhilGeis

    Member
    December 17, 2022 at 12:33 am

    @Bill_Toge
    The tests are effectively the same - some have more demanding criteria.
    None is validated.  Anything less than complete elimination of all but 16404 at 1st time point is suspect by any protocol.
    In anmy case, testing is not enough - one must consider manufacturing,  packaging, stability and anticipated consumer use.

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