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Glycerine as a preservative
  • ChemCuriousChemCurious
    I came across a shampoo formula that uses glycerine as the preservative. I was not aware that glycerine could be used in a formula containing water to preserve it. Actually I was not aware that glycerine could be used as a preservative at all. I understand that shampoo/body wash by their nature are not kind to microbes, but still, I would think you'd have to use a preservative with the water in the system. Am I missing something?
  • chummerchummer
    Jill -
    Glycerin is indeed a very effective preservative - in medicine, particularly herbal medicine,  you will frequently find glycerites as a delivery vehicle (especially in children's medicine) where the active component is preserved and then ultimately delivered in a water soluble solvent (glycerin) as an alternative delivery mechanism to alcohol. 
    To be effective as a preservative, you need to have AT LEAST a 50% glycerin content in your formula, and it is best if it is about 60-70%.  This makes it unpractical for cosmetic /personal care products, since it is not desirable to have a big sticky mess of a personal care formula. 
    Bottom line . . . it is great in medicine, but not at all practical in cosmetics.  Not at all practical for a shampoo base!  I sure would love to see that product!
    Cindy
  • ChemCuriousChemCurious
    I knew it was used in meds, but did not think it would be appropriate as a preservative in cosmetic formulas due to the amount needed to be effective. Not to mention this is supposed to be a dog shampoo formula (offered by an independent ingredient supplier) and I can't imagine using a huge amount of glycerine on my dog's skin.
    Here is their formula - though it is in fluid oz and measuring spoon amounts. I'm math-challenged and but I put in what I thought was about right. - without weighing it out not sure about the eo percentages.  That puts the glycerin at only 12.5% at most.  It's supposed to make (about) 32 fl oz:

    Water                              17 fl. oz               53%
    Glycerine                           4 fl. oz.             12.5%
    Plantapon LGC Sorb           8 fl. oz.         25%
    Cocamidopropyl betaine      3 fl. oz        9.5%
     
    Fragrance (optional)
    Citronella                           2 tsp
    Lavender                          1/2 tsp

    Cedarwood                       1/2 tsp

    Combine the water and the glycerine. Add the fragrance to the Plantapon LGC Sorb and mix well. Add the Plantapon to the water and mix well. Add the Cocamidopropyl betaine and mix well.


    Makes me a bit nervous when suppliers are putting this out there - I don't think it would kill anyone but if you made this and bottled it and used it on your dog it could cause problems over time. Especially if the eo's are not in proper amounts. That's 4 tsps of eo in a 32 oz batch - seems a bit high to me.
  • [Deleted User][Deleted User]
    Yeah, I wouldn't use that formula without adding additional preservative.
  • chummerchummer
    Hi Jill -
    Yeah, I agree that this formula definitely needs a preservative.  It could also use an emulsifier like Polysorbate 20 for improved incorporation of the EOs into the water-based formula
    Other than those 2 items, it generally looks OK.  When I first looked at the formula, I too thought the glycerin looked a bit much, but when you consider that soaps (handmade) contain ~25% glycerin, I am now inclined to think this is an OK amount for this shampoo.
    Also, the EOs work out to be about 1.5% of the formula, well within acceptable parameters.  You could go as high at 0.75 oz for this formulation; whereas as currently stated, it is roughly 0.5 oz..  Instead of using the EOs in the shampoo that will just add to the expense but get rinsed down the drain, I would incorporate them into a "coat conditioning" spritz to spray on the dog after shampooing, and that way they can be an effective bug deterrent.   And then for one more piece of added benefit, for the water component, I would put an infusion of oats into the water.  That should seriously help with the "itchies", as will the lavender in the EO blend.  If the dog is missing patches of hair, use Atlas cedarwood, other wise use Virginian cedarwood in the EO blend.  Both are very safe to use.
    By default, I do a lot of herbal remedies for wildlife (they come to our front door for medical help).
    Cindy
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