Full Spectrum Preservation

(Water-based hair serum formulation). For yeasts and moulds, if parabens, benzoic acid (derivatives) and sorbic acid (derivatives) are not to be used, what are some recommended alternatives for biocidal activity against yeast/mould and gram-positive bacteria? I have phenoxyethanol, phenyl ethyl alcohol, ethylhexylglycerin and benzyl alcohol at my disposal right now but I wonder if a combination between 2 of them could give me broad-spectrum preservation. Iodopropynyl butylcarbamate seems quite difficult to acquire at the moment. Any thoughts? 



  • It depends on the formula and pH, but phenoxyethanol + ethylhexylglycerin is the popular Euxyl 9010, which should provide great broad-spectrum coverage.

    Alternatively, phenoxyethanol + phenethyl alcohol can also provide robust coverage for ± bacteria, mold, and yeast. 

    But be aware that ethoxylated non-ionic emulsifiers like polysorbates can interfere with phenoxyethanol. 
  • > like polysorbates can interfere with phenoxyethanol. 

    I tried to find some data on this and wasn't able to. Is there a paper published?
  • PharmaPharma Member, Pharmacist
    edited October 22
    @chemnc Yes
  • Hello
    Yes, Euxyl 9010 is a great preservative, but, if you are formulating for Vegan or Natural Standards, it could be an issue.  For Phenoxyethanol, the Natural Standards in Europe, didn't like it in Concentration of 1% or more due to causing Irritation/Hypersensitivity.  For Ethylhexylglycerin, Based on EWG, It causes Allergies and Immunotoxicity.
    In a small Lab Batch, you may try:
    Spectrastat (Caprylhydroxamic Acid (and) Caprylyl Glycol (and) Glycerin):
    The issue in this one is some mfg. considers it "Pricey".  Also, It can cause separation / Drop in viscosity in some formulas based on the formula ingredients.  Also, you may try:
    Spectrastat OL : Caprylhydroxamic Acid (and) Caprylyl Glycol (and) Propanediol
    Spectrastat G2 Natural MB: Caprylhydroxamic Acid (and) Glyceryl Caprylate (and) Glycerin
    M-State: Magnolol (and) Honokiol (and) Caprylyl Glycol
    All of these Natural Ingredients are claimed to be Broad Spectrum, but, Practically, are they effective like the Traditional Preservatives (Euxyl PE 9010 , for example)? PET (Preservative Efficacy Test) should answer this question.
  • Thank you for your comments. 
    I have 4 more questions: 

    1. Aside from parabens and formaldehyde releasers and caprylhydroxamic acid, are there other cosmetic preservatives effective against gram-negative bacteria (much the way phenoxyethanol is)? 
    2. If I am to use sodium benzoate to preserve my product against gram-positive bacteria and mould, what pH is the best recommendation for use on the skin (in this case, the scalp)? 
    3. What percentage of sodium benzoate is suggested? I’m aware that 0.5% of benzoic acid present in the final product is the maximum allowable amount, but this may be excessive for the preservation I am after? 
    4. Would a combination of phenoxyethanol and phenyl ethyl alcohol or phenyl propyl alcohol really provide broad-spectrum preservation? I am skeptical about using ethylhexylglycerin due to reports of irritation (already a problem with phenoxyethanol, not desiring to exacerbate the potential issue further and the reason for which I inquire about an alternative preservative to phenoxyethanol). 

    Thank you! 

  • PerryPerry Administrator, Professional Chemist
    The EWG is not a science based organization, so their opinion related to ingredients should not be taken seriously.  That's not to say that they are wrong in all cases. But they are not a source of reliable information.

    Better is to refer to the CIR report on ethylhexylglycerin.
  • If you can get hold of it, I find Chlorphenesin pretty effective, especially in combination with something like Phenoxy
  • For what it's worth, I noticed that one high-end natural skincare manufacturer appears to be using both Spectrastat G2 Natural and a very small amount of phenoxyethanol.  This could be due to some tricky aspect of their formula, but I assume they must have tested things without the phenoxyethanol and found the formulation inadequately preserved.   
  • PerryPerry Administrator, Professional Chemist
    @suswang8 - It could also be that the phenoxyethanol is a preservative supplied with one of their ingredients so they don't actually add it themselves.

  • Interesting point.  Thank you.
  • Does phenoxyerhanol cause viscosity drop orthe polyohenolic citrus extract what I have at 1,5 percent in a gel formula. 
  • When I combined Phenoxyethanol 0.8 - 0.9%, Sodium Benzoate 0.1 - 0.3%, Potassium Sorbate 0.1 - 0.3% to use the blend as Broad Spectrum, I didn't find any problem with PET (Preservative Efficacy Testing), but, the results can vary from a formula to another
  • @JOJO91343 why would you use both sodium benzoate and potassium sorbate instead of just sodium benzoate when they both are used against mould and gram-positive bacteria? 
  • seaberryseaberry Member
    edited October 28
    @LuisJavier To my knowledge, potassium sorbate does better against gram negative but worse against gram positive bacteria compared to sodium benzoate. When used together, they can also boost each other's resistance to mold. 
  • @seaberry if gram-negative bacteria is already dealt with by using phenoxyethanol, then I find it redundant to use it, unless it could result in using less phenoxyethanol or if it’s more effective on different gram-negative bacteria species than the ones that phenoxyethanol eliminates. 
    The following link may be useful here: https://makingskincare.com/preservatives/

  • @LuisJavier
    That's just me missing the context, ha. 
    I was speaking in general terms about the use of potassium sorbate and sodium benzoate together. In theory, the two could negate the need for phenoxyethanol altogether in the correct pH and formulation, though it's not the most robust combination as a stand-alone preservative system. 
  • @seaberry I had no clue potassium sorbate had any effect on gram-negative bacteria. 
  • @LuisJavier This link shows sorbic acid's strong antibacterial activity towards S. aureus and weaker activity towards E. coli (Gram negative), which showed synergistic effects when paired with EDTA. 

  • @seaberry very interesting; I had a read of some of the pdf. I imagine that during PET, it is not only E.coli count that is tested for The category of gram-negative bacteria, although I suspect potassium sorbate may be effective on more than just this species of gram-negative bacteria. 
    Also, I had no clue that monolaurin was so effective too. I am interested in buying some monolaurin but have not found a source for it in the UK just yet. I was aware that coconut oil typically applied as a deodorant may have weak activity against some bacteria, likely due to the trilaurin. I suspect monolaurin or lauric acid are even more active in this regard due to having less of the glycerol molecules attached. 
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