In this post, Anonymous asks: Hi Susan, I have a question about glycerin. I have read that it can act as a preservative, but the amounts I've read where it's effective have been anything from 15-70%. I was wondering if I make a simple glycerin-water spray, with about 20% glycerin, if I need preservative or if the glycerin itself does the job. Also, if I add other things like wheat protein, panthenol, etc., would the glycerin act enough like a preservative for the whole mix?
It seems that you can use glycerin as a preservative when you use 50% glycerin or more in a product. (Click here for the Chemist's Corner comment, click here for the FDA slide.) It would preserve the entire recipe, so anything you add - proteins, panthenol, hydrosols, and so on - would be preserved as well. But would you want that much glycerin in a product? I can't imagine that would feel good. I think I've mentioned that I make a foot lotion recipe with 25% glycerin, and it feels great on my feet...but it feels awful on other parts of my body. I can't use it as a hand lotion - I have to wash it off after applying - because it's just too sticky. What would 50% feel like?
So you can't make a glycerin-water spray with 20% glycerin and expect it to be preserved. And I really wouldn't recommend a product of this nature.