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Home Cosmetic Science Talk Cosmetic Industry Using glycerin in liquid soap as a preservative

  • Using glycerin in liquid soap as a preservative

    Posted by Mags on February 11, 2022 at 8:25 pm

    Hi everyone.  I have read that using glycerin at at least 20% can act as a preservative.  Firstly, can anyone confirm or debunk that?  Secondly, if glycerin does act as a preservative, will the glycerin I add to my soap cook in place of water continue to act as a preservative even after the cook and dilution stage?  Thanks!  

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

    Professional Chemist / Formulator
    February 11, 2022 at 9:37 pm

    Glycerin is not a preservative. 

    It can be used to reduce water activity, but this does not make it a preservative.
  • Bill_Toge

    Professional Chemist / Formulator
    February 11, 2022 at 9:56 pm

    if you want it to prevent bacterial growth, you need a concentration of around 30-35% w/w, which will make any kind of liquid soap horribly sticky and seriously inhibit the foaming; if you want it to prevent the growth of yeasts and moulds, the required concentration is higher still

  • Mags

    February 11, 2022 at 11:12 pm

    @Bill_Toge, thank you for your response.  I agree with the sticky feeling and how it can inhibit foaming, which is why I was hoping that even after the cook and dilution stage it would continue to act as a preservative.  

    @Perry, I sent you a question about the natural cosmetic formulating course a few days ago, but I don’t see a response.  In summary, I was wondering if it would be suitable for someone like me who is very cautious (for many health reasons as well) about using broad spectrum preservatives including soy, corn and grain based preservatives that would be considered natural.  I am on the search for natural and alternative preservatives that are already considered natural and alternative.  Please message me when you get a chance.  

    I’d like to add, I add 2% citric acid and adjust the lye accordingly, as well as sodium chloride depending on the recipe to the liquid soaps.  Do they contribute as a preservative after the cook and dilution stages?  Thanks!!        

  • Abdullah

    February 12, 2022 at 2:31 am

    You can ether make a good product or bad product. You make good product by using ingredients that other good products use.

     Have you seen a good product that doesn’t use broad spectrum preservative?

  • PhilGeis

    February 12, 2022 at 11:28 am

    Glycerine is not a cosmetic preservative.  You’d need ~50% to prevent growth of bacteria and >60% for fungi. It only prevents growth - does not kill  as specified in preservative testing.   Users common add water to liquid soaps and shampoos  - an immediate compromise to glycerine “preservation”.   

    “Natural” preservation is basically BS.