Full-spectrum protection from preservatives

I’m planning on using phenoxyethanol in a o/w face serum with potentially around 85% water content. I’m aware that phenoxyethanol is not enough on its own for full-spectrum protection as it is mainly active on gram-negative bacteria with possibly some activity on gram-positive bacteria. For full protection, should I add some phenylethyl alcohol (PEA) to combat the moulds/yeasts or is this redundant if I’m using phenoxyethanol? Can I use the following in a leave-on face serum to add to the aspects that phenoxyethanol alone does not cover against: iodopropynyl butylcarbamate, o-cymen-5-ol, hydroxyacetophenone, Tropolone, nasaplin, Calcium propionate? 
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  • Also don’t mind using sodium Benzoate but would like to avoid formaldehyde-releasers, and potassium Sorbate (due to some people’s faces going red). 
  • Found an old post that has great information https://www.chemistscorner.com/cosmeticsciencetalk/discussion/751/preservation-strategies-for-natural-formulators

    I am using 0.7% Phenoxyethanol and 0.7% Benzyl Alcohol/EHG (Euxyl K900 which is itself claimed to be broad spectrum). Benzyl Alcohol if I’m not mistaken complements Phenoxyethanol as it covers gram+ bacteria, yeast and mold. And EHG enhances activity. I also add 0.2% EDTA.

    This is for my home made, personal use products and I have not preservative challenge tested my formulas, but so far I have not seen yeast or mold growth. 

    I had come across another post about how Polysorbate 80 and highly pegylated compounds can bind and inhibit preservatives. So you may want to share your formula so a more seasoned chemist can guide you better!
  • The only issue issue that I can see using benzyl alcohol with my face serum is if a drop of it were to accidentally go into someone’s eye or if the serum is used very close to the eye area as I read that benzyl alcohol can cause death to corneal cells. I don’t know if this should be a cause for concern. Thank you for the link that you shared. 
  • letsalcidoletsalcido Member
    edited April 2020
    I didn’t know that, so I did a bit of research and it seems that at the < 1% topical should be pretty safe. However, I suppose better safe than sorry. I am just curious to learn myself if this is something I should be cautious of now for my own products.

    I found a study about a drug (Kenalog) that reported issues https://pubmed.ncbi.nlm.nih.gov/16508436/ and determined that at the current usage it does not present toxicity in rabbits.

    That drug uses 0.99% Benzyl Alcohol as preservative and it’s injected into the eye https://www.aao.org/eyenet/article/intravitreal-kenalog-injections

    It’s possible that whatever actives you put in the serum would be potentially more damaging and prompt the user to rinse thoroughly.
  • We are paring phenoxyethanol with sodium benzoate, and ehtylhexylglycerin.
  • I didn’t know that, so I did a bit of research and it seems that at the < 1% topical should be pretty safe. However, I suppose better safe than sorry. I am just curious to learn myself if this is something I should be cautious of now for my own products.

    I found a study about a drug (Kenalog) that reported issues https://pubmed.ncbi.nlm.nih.gov/16508436/ and determined that at the current usage it does not present toxicity in rabbits.

    That drug uses 0.99% Benzyl Alcohol as preservative and it’s injected into the eye https://www.aao.org/eyenet/article/intravitreal-kenalog-injections

    It’s possible that whatever actives you put in the serum would be potentially more damaging and prompt the user to rinse thoroughly.
    I have this link for you that I remember reading on benzyl alcohol which is one of the reasons I avoid using it as a preservative in water-based skincare products: https://en.m.wikipedia.org/wiki/Benzyl_alcohol

    If you scroll down to and read the contact dermatitis and safety sections, you will see my concerns. 
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