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  • Microemulsion serum preservatives

    Posted by BathroomChemist on June 14, 2023 at 10:18 pm

    Hi all, new member here but I’ve viewed quite a few posts on preservatives already. Long story short, I’m formulating a microemulsion-based serum for a colleague’s cosmetics startup. The micelles are 30-40 nm, or 80-100 nm depending on the formulation. I’m using a proprietary oil blend (including 2.5% Vitamin E), Polysorbate 80 (P-80) as the surfactant (sometimes PEG400 as a co-surfactant), and water. My concentrates are 60% oil, 30% P-80, and 10% water, but my working concentration will likely be 20% oil, 10-15% P-80, and 65-70% water.

    Preservatives are of course the issue. My friend who’s a professor in pharmacology and an expert in dermal drug delivery likes parabens, but she cautions against using them due to negative public perception. Phenoxyethanol seems possible to use, and despite some people saying they’re inactivated by polysorbates, I found several papers showing enhanced anti-microbial activity. Would appreciate any clarification. Germall Plus (Powder) sounds fantastic, but I read that it failed for a few of you? I won’t use a low pH system, so sodium benzoate is out. What else should I consider that will be effective, and not cause a negative reaction (justified or not) from consumers?

    BathroomChemist replied 1 year ago 5 Members · 15 Replies
  • 15 Replies
  • BathroomChemist

    Member
    June 14, 2023 at 11:44 pm

    Quick update. I found the article “Compatibility and efficiency of preservatives in emulsive cosmetics containing high surfactant content”, which cited a paper claiming phenoxyethanol incompatibility with non-ionic surfactants. It also paints a grim picture for preserving micro and nanoemulsions with parabens, phenoxyethanol, and benzoic acid. Very interesting and worth a read. I’ll have to do more research on alternatives this weekend. I welcome any suggestions in the meantime.

  • Abdullah

    Member
    June 15, 2023 at 3:55 am

    I prefer DMDM over DU+EDTA+Chlorphenesin or IPBC

  • PhilGeis

    Member
    June 15, 2023 at 7:47 am

    Abdullah’s reco is a good one. Concerns for phenoxy in this context are valid and are addressed with data not dogma.

    • Adamnfineman

      Member
      June 16, 2023 at 11:26 am

      Hi Phil,

      Do you happen to know where I can read up on some of this data? A few of our products use phenoxyethanol and polysorbate-80. I was able to find another forum post when looking online but I don’t have access to any of the studies I found except the one sent by the original poster there.

      Thank you for your time,

      https://chemistscorner.com/cosmeticsciencetalk/discussion/inactivation-of-preservatives/

      • BathroomChemist

        Member
        June 16, 2023 at 11:43 am

        I know you addressed this to Phil, but I may be able to provide a bit of guidance here. Many sources that talk about the incompatibility of phenoxyethanol with non-ionic surfactants can be traced to a single reference, which is “Sheskey PJ, Cook WG, Cable CG. Handbook of Pharmaceutical Excipients”. I got free access to the 6th edition. On Page 489, it says, “The antimicrobial activity of phenoxyethanol may be reduced by interaction with nonionic surfactants…[14]”. The citation for this is “Lee MG. Phenoxyethanol absorption by polyvinylchloride. J Clin Hosp Pharm 1984; 9: 353–355″.

        • Adamnfineman

          Member
          June 16, 2023 at 12:43 pm

          Thank you very much. It looks like I have some weekend reading to do : )

      • PhilGeis

        Member
        June 17, 2023 at 8:47 am

        I meant your data. We do it them in media to neutralize preservatives but you can find polysorbate in many products effectively preserved with phenoxy, parabens etc.

  • BathroomChemist

    Member
    June 15, 2023 at 9:25 am

    Thanks all, I just added a 2 oz bottle of DMDM to my cart on Making Cosmetics. It sounds like many of you are fans of DMDM based on other posts about preservatives.

    Another interesting one I found last night was <font color=”rgba(0, 0, 0, 0)” face=”inherit”>Silverion 2400 by PURE Bioscience. I’m normally </font>skeptical of silver-containing products, but it’d be unfair to write silver off. I used to work in a field where researchers were impregnating porous clays with silver nanoparticles to purify water in the developing world. Anyone have experience with this product? pH would need to be below 7, but it’s supposedly compatible with non-ionics. I’ll try calling the company today and report back.

  • ketchito

    Member
    June 15, 2023 at 10:02 am

    @BathroomChemist just out of curiosity, how do you confirm you’ve got a microemulsion? Did you use some microscopy or diffraction technique? Did you get a blue-ish look on your serum? Usually for stable microemulsions, the use of small alcohols and specific surfactants are needed (unless you use linkers and many other funny stuff to get the required curvature), not to mention the type of oils in your oil phase…so having only polysorbate 80 as sole surfactant intrigued me. Good luck!

    • BathroomChemist

      Member
      June 15, 2023 at 10:35 am

      Hi Ketchito, I have access to cryo-EM and a Zetasizer so I can characterize size and surface charge. I’m doing some tricky things with the oil phase, and that got me a microemulsion range over 67% of my ternary plot (10-80% of each ingredient, increments of 10%). If I dilute the samples (1:2 ME:Water) this area drops to 50% (adding a tiny of PEG400 to hazy vials increased this to 59%). The microemulsions are transparent and very fast absorbing. A few samples are the slightest bit hazy, and a few are translucent with a brilliant opalescence. I haven’t measured the size of these, but they’re probably something like 100-200 nm. I’ve stabilized those sample with a tiny bit of PEG400.

      What small alcohols do you recommend? I tried n-butanol for the fun of it because I happened to have some in my bathroom, and it cleared some of the cloudy (diluted) samples, but that’s obviously not suitable for cosmetics!

      • ketchito

        Member
        June 16, 2023 at 9:14 am

        @BathroomChemist Sweet! Back in the day I had a very nice microemulsion for a laundry detergent. I didn’t have small alcohols at hand (pentanol and hexanol are used quite some in papers I found), so I used gasoline instead (I know, I know…not something you’d have in your bathroom) and it worked! I also used octyl disuccinate as hydrophilic linker. Nevertheless, I never managed to increase its viscosity without altering the system, so I drop the formula. Good luck with your project!

  • BathroomChemist

    Member
    June 15, 2023 at 3:23 pm

    So I called PURE Bioscience to ask about Silverion 2400, and while it is listed as being compatible with Polysorbate 80, the R&D lead said that only applies to a low percentage. My concentration is way too high. I think I’ll order the DMDM, but I may also explore another surfactant like Kollophor EL (PEG-35 castor oil) to replace the Polysorbate 80. Anyone have experience using these, or know preservative compatibility?

  • PhilGeis

    Member
    June 15, 2023 at 3:54 pm

    DMDMH is a good idea - the more water soluble the better.

    • BathroomChemist

      Member
      June 29, 2023 at 9:52 am

      Hi Phil (and others), I just wanted to give some updates on preservatives, especially since I had success, at least so far, with one of your recommendations. I purchased Hexylene Glycol to use at 10% based on published work showing broad anti-microbial activity at this percentage and compatibility with non-ionic surfactants, as well as DMDMH, silver citrate (despite manufacturer warnings), and a 3:1 mix of Caprylyl Glycol (CG) and Ethylhexylglycerin (EHG).

      The Hexylene Glycol ruined my microemulsion. The silver citrate slowly precipitated out despite a pH of 5.5, which is in range. DMDMH at 2% and CG/EHG at 2% worked very well, at least in terms of preserving the microemulsion. I used double the recommended amounts of each to look for instability. I excluded every other common preservative (e.g. parabens, phenoxyethanol, benzoic acid, sorbic acid) because none of them are compatible with non-ionic surfactants > 5%.

  • BathroomChemist

    Member
    June 16, 2023 at 11:38 pm

    So I scanned the entire 900 page handbook of excipient and looked at papers as far back as the 1950’s (which unsurprisingly used mercury containing compounds and dioxane because it’s the 1950’s) and I compiled a list of potential preservatives to use or not to use with non-ionic surfactants. Hopefully this will be helpful to others in the future:

    Compatible: Sorbic acid, hexylene glycol, Imidazolidinyl urea (and likely diazolidinyl urea), propylene glycol (needs > 15% for antimicrobial activity)
    Likely compatible: DMDM Hydratoin (compatible with non-ionic surfactants according to Ataman chemicals but no concentration specified)
    Limited compatibility: Silver citrate (up to 2% surfactant), benzoic acid (antimicrobial activity partially reduced), benzalkonium chloride (incompatible at higher surfactant concentrations), chlorhexidine (incompatible at higher surfactant concentrations)
    Incompatible: All parabens (10% propylene glycol protects against Polysorbate 80), phenoxyethanol, cetrimide, Chlorocresol, Chloroxylenol, m-Cresol

    A paper from 1957 showed excellent activity against modern test organisms with 0.2% sorbic acid, 3% hexylene glycol, and a combination of these two. Note that surfactant concentrations rarely go above 5% in these tests. Also note that the list above is not authoritative and not quantitative for the most part (e.g. sources may not clarify what “higher surfactant concentrations” means). It’s just a compilation of what I found with a cursory literature review.

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