Home Cosmetic Science Talk Formulating Impossible preservative challenge- need help!

  • amorical

    April 16, 2020 at 5:49 pm

    Okay, so I tested ph again and came out with what I suspected, around 9.8.

    I tried a blend of 2% BIT and 8% sodium pyrithione at 1% of the formula. I put a dab of the result on my face and it stung after a while. Not that this is face paint but I don’t want it to sting if it happens. 

    Hmmm… if you wanted to maintain hydration, you could switch glycerol for 1,2-hexanediol alongside some less traditional preservative.

    I’m confused. How would this help me? Is something wrong with using the glycerol? I would be okay lowering water activity, but I’m not totally sure how…

    I have not been able to get samples of the pentylene glycol, propanediol, caprylyl glycol, ethylhexylglycerin and chlorophenesin blend because of covid, but I’m still curious as to your thoughts on it. Would it work or is it just a blend of boosters?

  • pharma

    April 16, 2020 at 7:00 pm
    Unfortunately, the amount of glycerol in your product is way too low to noticeably affect water activity. Had you told me it contains 20% or so…
    There is nothing wrong with glycerol just that switching it for hexanediol or pentylene glycol would give you a marked increase regarding microbial stability whilst maintaining more or less the same effect of glycerol. This way, chances are higher that an alternative preservative will work or, at least, that the amount of traditional preservatives can be kept low.
    I have zero experience with your blend. Combining a booster with cayprylyl glycol or the like and an acidic or a phenolic
    preservative (traditional or alternative) is state of the art and makes total sense. It seems to me a bit superfluous to combine an old antimicrobial (chlorphenesin) with caprylyl glycol (antimicrobial/booster) and 3 ingredients which mostly act as boosters. There is not much logic behind that, if you ask me.
    Astonishingly, chlorphenesin is often added to alternative preservation systems (it’s also used widely in technical products and soaps, mostly in the USA). My speculation is that it’s added because first, other alternative/natural preservatives didn’t work, second, it also acts as cosmetic biocide (killing microbes on skin = deodorising and anti-comedogenic), and third, though it’s on the ‘ugly’ list, nobody cares about it. In my opinion, whoever adds chlorphenesin to a modern product earns a beating for being lazy 🙂 . Chlorphenesin should either be replaced with a ‘real’ but environmental friendly traditional preservative or one should go the extra mile finding a true alternative system combined with for example triethyl citrate and/or sodium caproyl/lauroyl lactylate for the ‘biocide effect’.
  • bill_toge

    April 16, 2020 at 7:33 pm

    for what it’s worth, sodium pyrithione is VERY toxic; the reason zinc pyrithione is used in its place is because it’s much less soluble in water, hence less bioavailable

  • czkld

    April 17, 2020 at 6:37 am

    Aren’t isothiazolinones banned for use in leave-on applications regardless?

  • pharma

    April 17, 2020 at 2:12 pm
    Sodium pyrithione and benzisothiazolinone are usually used for in-can preservation of paint…
    I couldn’t find much useful about SPT. Seems as if it’s still under investigation whether or not it should be a regulated substance for paint preservation. Given the better water solubility, it might be safer on skin than ZPT which is regulated and only allowed for rinse-off and hair products.
    Same goes for BIT. The proposed maximal concentration is 100 ppm (or 0.01%).
    From what I could find, both are neither in any negative nor any positive list regarding cosmetic ingredients.
    Personally, I wouldn’t use either of the two.
  • amorical

    April 17, 2020 at 7:33 pm

    When I have tried to increase glycerin it results in a slimy stickiness that is not super great. I can try again though. I like what I’m reading about 1,2-hexanediol, except that it is volatile.

    Thank you to everyone for your thoughts and help. I am not attached to the BIT or SPT, just trying to problem solve and feeling like I’m running out of options. 

    I am thinking of hiring a formulator to help figure it out, unless anyone has any fabulous solutions. What works at 9.8 ph, that doesn’t hurt peoples skin, and doesn’t contain vocs? Anything? 

  • pharma

    April 17, 2020 at 8:09 pm

    amorical said:

    …I like what I’m reading about 1,2-hexanediol, except that it is volatile.
    …I am not attached to the BIT or SPT, just trying to problem solve and feeling like I’m running out of options. 

    I am thinking of hiring a formulator to help figure it out, unless anyone has any fabulous solutions. What works at 9.8 ph, that doesn’t hurt peoples skin, and doesn’t contain vocs? Anything? 

    Only if your AC is broken and your flat heated up to over 200°C ;) .
    Seriously, it’s not a VOC and boils at a temperature where several other cosmetic ingredients have already self-ignited or charred. If you’re still in doubt, go with caprylyl glycol, a closely related antimicrobial diol with a 20°C higher boiling point (i.e. ~240°C). But again, whatever boils above 100°C and hasn’t a high vapour pressure is far from being volatile or considered a VOC. On the other hand, essential oils though having equally high boiling points as hexanediol still evaporate at room temperature due to high vapour pressure and therefore are VOCs.
    Why don’t you want phenoxyethanol? It boils at 250°C and, although it has a vapour pressure high enough to ensure head space preservation, it is not a VOC plus it is stable at pH 10.
    BIT on the other hand is an isothiazolinone and IIRC, you don’t want that in your product, do you?
  • amorical

    April 17, 2020 at 9:00 pm

    Phenoxyethanol isn’t a voc??? I definitely thought it was and definitely read somewhere that it was! I can’t find where I read that though… Unfortunately I don’t know enough chemistry to know if something is a VOC or not other than by google research.   :s 
    That’s totally a game changer! 
    So I could just use phenoxyethanol and caprylyl glycol or ethylhexylglycerin? What pairing would you recommend?
    This is so exciting!! I crossed it off my list eons ago! Thank you so much. 

    Good to know about the 1,2- hexanediol! I will look into that more too. Maybe it will have less stickiness factor? Talking to people who actually know what they’re talking about is equal to hours of research to me.

  • amorical

    April 17, 2020 at 9:19 pm

    Could you explain why there is so much contradictory information on whether phenoxyethanol is volatile or not? All the little mentions I find about it say differing things? Not doubting you, just trying to understand.

  • amorical

    April 17, 2020 at 9:21 pm

    Are formaldehyde donors VOCs? I’m just doubting everything now.

  • oldperry

    April 17, 2020 at 9:56 pm

    I do believe Phenoxyethanol is a VOC.  At least according to the EPA.

    No, formaldehyde donors are not VOCs, although formaldehyde is.
    Here is what the California Air Resources Board lists as VOCs.

    Whether something is a VOC or not is a regulatory question. The answers don’t always make scientific sense.

  • pharma

    April 18, 2020 at 6:17 pm
    Mea culpa!
    Sorry, my brain must have had the hickups…. it’s not boiling point above 100°C but 240-260°C.
    So, I did some research: Turns out that the limit of 240°C is only here in Switzerland where phenoxyethanol is indeed not regarded as VOC. In the US it’s 250°C and/or photochemical reactions (likely to happen) and in the EU 260°C. Vapour pressure for all is well above phenoxyethanol and hence, boiling point should theoretically be irrelevant but alas, as @Perry said, there is not much rational basis behind what’s considered a VOC and what not and therefore huge differences exist between different countries/regulatory organs.
    Phenoxyethanol has a boiling point of 247°C. Fu#*@ ;( ;(
  • Halim

    May 11, 2020 at 4:04 pm

    I have some experiance on paint
    you can solve this problem with 2 way
    1- If possible you must keep pH between 10-10.5 this is very troublesome
    ın my test ı cant keep pH 
    2 - If your system is opauqe you can use Omya Smart Zero
    ıts powder form and dont includes Voc
    NaPy-ZnPy dry film preservatives They are not suitable for in can protection and with
    2 phenoxy ethanol you will have Voc

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