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Inactivation of preservatives by surfactants?
In the book “Surfactants in Cosmetics”, page 585 [1], it states that nonionic surfactants interfere with common preservatives as: phenoxytanol, benzyl alcohol, alcohol (ethanol) and reduce their action. So a higher percentage of preservatives should be used when working with nonionic surfactants.If I use a concentration of 1-2% polysorbate-80 in my formula, would it affect that much of my preservative system?My formula:- Water - 84%
- Glycerin - 2% (moisturizer/humectant)
- Polysorbate-80 - 1-2%
- Zinc sulfate - 1% (active)
- Caffeine - 0.4% (active)
- Ethanol - 12% (penetration enhancer, preservative)
- Phenoxyethanol - 0.4% (preservative)
In your opinion are my preservative concentrations enough? Should I increase or change something to prevent overgrowth?From a 2014 study from the Journal of Cosmetic Science, an ethanol concentration higher than 16% exempts product of challenge test [2]. And a concentration of .32% phenoxyethanol inhibits gram negative bacteria, mold & yeast [3].Thank you! -
4 Replies
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Citation 2 mentions “ It has been shown that an ethanol concentration between 10.5% and 16%, and an glycerine concentration >10%; “.
What kind of water are you using (distilled, deionized, boiled)? Zinc can promote yeast growth but I’m no expert in that subject so I don’t know if your 1% is troublesome or not.
Ultimately we can all give opinions but you won’t know without challenge testing.
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You should be OK with the ethanol in there, but why do you need the surfactant anyway? I see no need for it.
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12% ethanol will keep most but not all germs from growing and it won’t kill any.The 2% glycerol are, at that concentration, bug food at best whereas zinc sulfate at 1% hampers microbial growth (likely not of all but of many).The 0.4% phenoxyethanol should put your product in a safe spot.Is it a spray? Else, I concur with @chemicalmatt: Why a surfactant?BTW most scientific and most older literature uses the term nonionic surfactant for PEG derivatives. The inhibitory effect of modern nonionics on preservatives is largely unknown. Given that you use a surfactant without any oil phase increases the chances for inactivation of phenoxyethanol, no matter which type of surfactant you use. However, the more ethanol and glycerol you add, the smaller that chance gets. -
Thank you very much for the answers, I really appreciate them!I am sorry for opening a new discussion for the same problem, as now, I saw this question has already been asked here numerous times before.Link to other threads with the same question:
- https://chemistscorner.com/cosmeticsciencetalk/discussion/6818/inactivation-of-preservatives
- https://chemistscorner.com/cosmeticsciencetalk/discussion/3685/preservative-questions
- https://chemistscorner.com/cosmeticsciencetalk/discussion/56/cosmetic-microbiologist-here-i-can-help-answer-your-germ-questions
- https://chemistscorner.com/cosmeticsciencetalk/discussion/450/nonionic-surfactants-inactivate-phenoxyethanol-and-benzyl-alcohol
- https://chemistscorner.com/cosmeticsciencetalk/discussion/6507/preservative-for-nonionic-surfactant-shampoo
Ultimately we can all give opinions but you won’t know without challenge testing.Very true! But cosmetic formulating is like a side hobby for me at the moment, not my specialty, and a challenge test where I live seem to cost around 240 USD dollars. Is this a normal price for CT’s?
What kind of water are you using (distilled, deionized, boiled)? Zinc
can promote yeast growth but I’m no expert in that subject so I don’t
know if your 1% is troublesome or not.I am using distilled water. I do not know the exact effect of zinc sulfate on fungus, although other forms of zinc (pyrithione & oxide) seem to be used as a antibacterial & anti-fungal agents in cosmetics.- https://www.sciencedirect.com/science/article/pii/S0378517314009284
- https://pubmed.ncbi.nlm.nih.gov/26885780/
- https://pubmed.ncbi.nlm.nih.gov/15316263/
12% ethanol will keep most but not all germs from growing and it won’t kill any.The
2% glycerol are, at that concentration, bug food at best whereas zinc
sulfate at 1% hampers microbial growth (likely not of all but of many).The 0.4% phenoxyethanol should put your product in a safe spot.Thank you for the answer!BTW most scientific and most older literature uses the term nonionic
surfactant for PEG derivatives. The inhibitory effect of modern
nonionics on preservatives is largely unknown.I looked trough a large part of products containing polysorbates, and most of them use exactly phenoxytanol as a main preservative, some with the addition of an another one e.g. potassium sorbate. So maybe there is some truth about this “deactivation”, but it is mostly exaggerated?Is it a spray? Else, I concur with @chemicalmatt: Why a surfactant?Well, yes, it is a spray, but I use it in a glass bottle with a dropper to apply it more efficiently at my follicles, but it can be used in a spray bottle also. I honestly don’t know whether I need a surfactant or not. The spreadability of my product is awful. It sprinkles when I try to rub it in, and it doesn’t spread evenly though the scalp.I read that surfactants lower the surface tension and aid in the spreadability of products when applied to the skin and thought that maybe this is what I need? Should I use something different? Maybe a thickener, xanthan gum?Thank you!
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