Preservative questions - Cosmetic Science Talk

Preservative questions

I'm still having a lot of doubts about preservatives...

How do you deal with (partial) hydrophobic preservative(s) (blends)?

For example, phenoxyethanol is added to the cooling down phase, due to its volatility, but won't it migrate to the oil phase instead of being active in the water and oil/water interphase?

* I want to try a few blends, but am not 100% sure in which phase to put them or to pre-mix with a water miscible solvent first:
Blend 1: phenoxyethanol (90%) + ethylhexylglycerin (10%);
Blend 2: 68% Benzylalcohol 
              26% Methylparaben 
              6% Propylparaben
              0,1% BHT (to inhibit benzyl alcohol from oxidizing).

* I know non-ionic surfactants can deactivate some preservatives, like phenoxyethanol, parabens. But inspite of that, I see them combined all the time. Is this really something to worry about? Or is this only with polysorbates?

* And last but not least: packaging.
I read that low to medium density polyethylene is able to absorb parabens from a formulation and benzyl alcohol and phenoxyethanol are known to interact with polyethylene and polystyrene.
But aren't most packages made of polyethylene?
What are your thoughts on this?

Thank you!:-)
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Comments

  • phenoxyethanol and benzyl alcohol are water-soluble, though sparingly so - very little of either will partition into the oil phase, so the answer is put them in the water phase

    substantially water-soluble ethoxylated surfactants, e.g. SLES, can reduce the activity of some preservatives; they won't deactivate them outright

    regaring packaging, I've never seen any of these phenomena occur in practise; this appears to be one of those urban myths that has somehow become received wisdom despite not having a shred of evidence to support it
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • Parabens can be inactivated by polysorbates via micelle binding.
  • edited November 12
    The "myth" that parabens get absorbed may come from food industry where migration of chemicals from /into plastic packaging is important as they can end up in the food. However, that all parabens somehow will migrate into the packaging is not realistic.
  • @Bill_Toge
    So it doesn't have to be added to the cooling phase due to its volatility?
    Both blends I mentioned can be added to the water phase as well, I reckon?
    Glad to read that whole packaging thing is an unsupported urban myth. You're right, I never see links to researches when they state those interactions.

    Thanks everyone!
  • edited November 13
    @Doreen81 it has a boiling point of 247 °C at atmospheric pressure, so it's not particularly volatile
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • So is there any truth to phenoxyethanol being inactivated by polysorbates? I know this has been around for a while but I've never seen any data.
  • @Bill_Toge
    You're totally right, silly me! I think I got confused because of this sentence "Phenoxyethanol has the advantage that it is slightly volatile so it will protect the “head space” or vacant air space above the product in the bottle." on the site of Making Skincare.
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