Home Cosmetic Science Talk Formulating Preserving an Alkaline Glycol-based Deodorant

  • Preserving an Alkaline Glycol-based Deodorant

    Posted by erindlea on February 15, 2016 at 9:14 pm
    My aluminum-free deodorant stick formula has the following ingredients: 

    Propanediol, Magnesium Hydroxide, Glycerin, Aloe Vera Juice, Sodium Stearate, Behenyl Alcohol, Arrowroot Powder, Kaolin, Castor Oil,  Hops Extract, Cetearyl Alcohol, Glyceryl Stearate, Essential Oils, Phenoxyethanol, Ethylhexylglycerin, and Sodium Chloride

    Because of the aloe vera juice and arrowroot starch, I have been using a preservative at 1% (phenoxyethanol and ethylhexylglycerin blend). I notice that many aluminum-free deodorants on the market have a similar ingredient list that includes botanicals, but most of them do not list a preservative. I’m now wondering if a preservative is necessary. My water phase plus botanicals make up less than 25% of the total formula, and the glycols make up more than 50%. Would the high percentage of glycols, combined with the pH of ~10 discourage the growth of microbes? Should I still use a preservative, and if so, is 1% necessary, or could it possibly be reduced?
    microformulation replied 7 years, 9 months ago 5 Members · 5 Replies
  • 5 Replies
  • belassi

    February 15, 2016 at 10:16 pm

    The only way to be sure of that is to test it.

  • oldperry

    February 20, 2016 at 5:03 pm

    Theoretically, but as @Belassi said, you have to test it.

  • MarkBroussard

    February 20, 2016 at 8:22 pm

    Look at it this way … the whole idea of a deodorant is to kill the bacteria that break down sweat and cause the odor … any ingredients that kills bacteria is good is an deodorant.

  • belassi

    February 21, 2016 at 12:20 am

    What are the essential oils and in what concentration? You can check the MIC (minimum inhibitory concentration) figure for essential oils and if you include enough of the right type, taking the MIC well above the averages for bacteria and fungi, you should have a safe product.

  • microformulation

    February 21, 2016 at 12:39 am

    But again, you will never really know unless you have it tested. In a perfect World this testing would be mandatory. In the case where there is any doubt whatsoever (and be honest and conservative), Preservative Effectiveness Testing MUST be completed.

    Preserving with a Glycol utilizes the concept of Water Activity (Aw). Here is a link to an albeit dated outstanding presentation by one of the Industries experts. He covers Water Activity and the Hurdle Concept on pages 22 to 25. The big take away should be Water Activity “Must be measured, not calculated.” http://www.midwestscc.org/blog2/wp-content/uploads/presentations/Jan2012CurrentTrendsinCosmeticPreservation.pdf

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