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  • Microbial challenge testing on W/o or w/silicone emulsion

    Posted by Anonymous on April 3, 2014 at 10:08 am

    Hi, I was told if an w/o emulsion formula with high hydrophobicity, it is not suitable to put on micro-challenge testing, due to the fact that bugs would not get the chance to go into the inner phase to contaminate the product. For example, 25% water,3.5% glycol, 1%NaCl in water phase, 30% pigments and powders, the rest is typical WE09 and EM90 and emollient. Any professional idea on it? Thanks.

    Anonymous replied 9 years, 8 months ago 3 Members · 6 Replies
  • 6 Replies
  • oldperry

    April 3, 2014 at 11:31 am

    I think you should still do micro testing to be safe.  And you should include a preservative just in case there was some problem during manufacture.  However, water in oil emulsions typically require less preservation.

  • Anonymous

    April 3, 2014 at 12:15 pm

    I was told to just test the water phase with preservatives, and not test the final product. This formula has high risk failing the challenge due to the fact that it has high content of powders and pigments to me. I would appreciate any other microbiologists and chemists comment on it.

  • the_microbiologist

    April 3, 2014 at 12:59 pm

    I agree with Perry’s “better safe than sorry” approach.

    I recommend running the challenge test on the intact formula, using approaches laid out in CTFA M-6.  Depending on oil/water content the approaches vary, but the idea is to modify the inoculum by diluting it in light mineral oil or emulsifying it, then introducing it to the product.  I don’t think most contract labs run that method, so I’ll tell you that Cosmetic Test Labs does just as FYI.

    Good luck!

  • Anonymous

    April 3, 2014 at 4:25 pm

    Thank you microbiologist! That is what I was thinking to use more tween to neutralize the test product based on USP guideline, but I don’t have any procedures to support me. We have micro-lab, but just need to change procedures and need some docs.  to back up. 

  • pma

    April 4, 2014 at 5:09 am

    Although it wasn’t your question, phenoxyethanol usually is enough for W/Si emulsions - if the the water content is really low of course. 

    Most W/Si emulsion in the market are preserved with (and only) phenoxyethanol. 
  • Anonymous

    April 4, 2014 at 11:26 am

    Hi Microbiologist, where i should down load the CTFA M-6 official guide? 

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