When to add preservative in the formula?

Usually, formulas have preservative as their last ingredients. However, in an o/w emulsion, I added a preservative to my water phase and heat, then mix the oil phase to the water phase. I wonder if there is a difference if you add a preservative to water phase first and heat up will all water phase or you must add it in the end? Is it Ok to heat up the preservative? Thank you.


  • Yes, there’s a difference. You need to consider what temperature your preservative can tolerate and many other factors. 
  • MarkBroussardMarkBroussard Member, Professional Chemist

    The question is:  Why do you feel the need and/or want to add your preservative to the hot water phase?  If you don't have a compelling or necessary reason, then why take an unnecessary risk?  

    Most preservatives are going to be heat stable and can tolerate 70C, but not all.  You would have to check on the heat stability of the specific preservative you are using.
    Chemist/Microbiologist formulating in the Organic & Naturals arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program guidelines focused skincare & haircare products. 

    See website for details www.desertinbloomcosmeticslab.com
  • For example you can't add preservative to the waterphase when you make hair conditioner. Cationics such as BTMS and Behentrimonium Chloride have very high melting point. The data sheets say 90C but in my experience it's close to 100C. I don't know a preservative that would tolerate it.
  • jyyjyy Member
    Thank you all.

    I checked that the preservative I used, euxyl® K 940 from Schülke Inc, has maximum temperature 100C and I heated the water phase only to 75C. I guess it would be fine then. 

    I will keep in mind to add preservative after the mixture cools down just in case. Thank you.
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