Effective preservative system

What's one fail-proof preservative you would recommend for all sorts of formulations (serums, toners, moisturizers, etc.) between a pH of 3 and 8?

Comments

  • PhilGeisPhilGeis Member, Professional formulator
    There is no such system.
  • PerryPerry Administrator, Professional Chemist
    If it was that easy, everyone would be using it.
  • PhilGeis said:
    There is no such system.
    I thought for sure you and @Perry would have come back with some paraben blend + an F releaser as a one size fits all?  Really...no?  Is pH the limiting factor....of not being able to create a one size fits all?
  • PerryPerry Administrator, Professional Chemist
    @Graillotion - Honestly, each system is different. If your formula has polysorbates in it then parabens are not your best choice. In truth, Kathon works pretty well in a wide range of formulas but then it has a problem of sensitization.  The limiting factor is the particular ingredients used in each unique formula.

  • Perry said:
    @Graillotion - Honestly, each system is different. If your formula has polysorbates in it then parabens are not your best choice. In truth, Kathon works pretty well in a wide range of formulas but then it has a problem of sensitization.  The limiting factor is the particular ingredients used in each unique formula.

    Why are polysorbates and parabens incompatible? 
  • Perry said:
    @Graillotion - Honestly, each system is different. If your formula has polysorbates in it then parabens are not your best choice. In truth, Kathon works pretty well in a wide range of formulas but then it has a problem of sensitization.  The limiting factor is the particular ingredients used in each unique formula.

    Secondly, if a preservative is oil-soluble, can it be solubilised with, say, a polysorbate and used in a water-based formula?
  • PharmaPharma Member, Pharmacist
    ifamuj said:
    Why are polysorbates and parabens incompatible? 
    We don't know why and they aren't just incompatible with polysorbates but several nonionic emulsifiers as well as a bunch of other cosmetic ingredients. There are speculations about parabens interacting with the hydrophilic PEG chain by hydrogen bonding and thereby accumulating in the interphase instead of remaining in the water phase. Parabens are better soluble in 'intermediate' solvents (such as alcohols, glycols, or PEGs) than in water or oils.

    Regarding your second post/Q:
    A preservative has to be located, at least partially, in the water phase in order to act as preservative. However, many also require a certain preference for lipophilic media so that they can cross microbial membranes and cell walls. A typical distribution between water and octanol (a common approximation for the distribution of chemical compounds between water and cell membranes) for such preservatives is 1:100-1:1'000. In other words, they are rather well soluble in oils and/or solvents but  not necessarily super water soluble. Therefore, several oil soluble preservatives are available but will be incorporated at levels low enough to result in partial dissolution in the water phase without the aid of emulsifiers.
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