Wednesday, June 20, 2012

Question: Can glycerin act as a preservative?

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.


Rae said...

Hi susan, how long can a 10% glycerin + water solution last if I store it in the fridge.

p said...

I've seen differing information on the percentage of glycerin required for preservation. For example, here the FDA says that 10% glycerin makes a product self-preserving:

"Some cosmetics, i.e., those containing more than about 10% ethanol, propylene glycol, glycerol, etc., and cosmetics in self-pressurized containers, are self-preserving and are not likely to become contaminated with microorganisms." Source:

10% seems really low to me. I wonder if 10% glycerin is enough to lower the water activity to prevent bacterial growth but not fungal growth (though if so I'm not sure why FDA would make the statement above!).

I think the FDA slide linked to in the post is for medicine (though I don't sure why the figure for medicine should be so different than for cosmetics!).

Anonymous said...

Thanks for answering my question! I notice a lot of the hair forums and blogs recommend a spray for the hair at about 1 in 5, and I always thought, eek, doesn't that need preservative, but then read that amount might be self-preserving.

p, that's interesting... this is why I found this so confusing, I was coming across very different figures from different sources. I wonder if the 'self- pressurized containers' is key there?

Susan Barclay-Nichols said...

Hi Rae. Are you preserving it? If not, then a few days at the most. (I wouldn't trust anything without a preservative, and glycerin can be very tasty and appealing to various beasties, so I wouldn't use it without a preservative at all.)

Hi p. I'm with anonymous - I think the key might be the "self-pressurized containers" part. I will do more research here.

Hi Anonymous. Why are you using glycerin on your hair?As a humectant? Doesn't it feel really sticky?

p said...

Hi Susan and Anonymous,

I think that'd be a reasonable guess as a formulator, but I don't think that's what the sentence says:

"Some cosmetics, i.e., those containing more than about 10% ethanol, propylene glycol, glycerol, etc., and cosmetics in self-pressurized containers, are self-preserving and are not likely to become contaminated with microorganisms."

I think "cosmetics containing more than 10%..." and "cosmetics in self-pressurized containers" are two separate sets of products (otherwise why would they use the word 'cosmetics' a second time)? There's nothing gramatically and logically that suggests that both conditions ('more than 10%' and 'self-pressurized') need to be met at once for the conclusion (self-preserving) of the sentence to hold. Likewise, I don't think the sentence is about products that contain 10% ethanol, 10% propylene glycol, 10% glycerol, 10% etc. all at the same time!

Susan Barclay-Nichols said...

Hi p. Wow, i must be a little tired this morning. I totally see that now! My husband is calling me for a lovely breakfast, so I better run. Perhaps my brain will work better after some food!

Anonymous said...

Thanks for the great post. I think I am following what previous posters said. It seems to have been a while back, but hope you do get to see this and answer it.

I was wondering about adding a bit of glycerine <5% to a hydrosol mixture. The hydrosols by themselves do not need preservatives; the glycerine itself doesn't need a preservative, so would it be accurate to assume that the mixture (glycerine + hydrosol) as a whole would not need a preservative?

PS: Thanks for a great site.

Anon 2

J said...

Hi Susan~ I am planning to use glycerin to preserve stains. Will the stain be sticky because it has glycerin? Does glycerin become sticky after some time?
How can I do the percentage stuffs of the glycerin?

Susan Barclay-Nichols said...

Hi J. I'm sorry, but I don't understand the question. You're preserving a stain?

nana said...

Hi Susan, thanks for what you do. I will like to make a balm (with solid and liquid oils without water) and will like to use about 20% glycerin. I am wondering since glycerin is like water, will i need to add a preservative to my balm? If so which paraben free preservative do you think will work. Or can i just do ROE with vitamin E? Thank you.


Susan Barclay-Nichols said...

Hi Nana. If you are adding glycerin, you need to add an emulsifier and a preservative. You can learn more about preservatives in the preservatives section of the blog, and you can check out the FAQ for more information on emulsifiers. ROE and Vitamin E are not preservatives, they are anti-oxidants, meaning they retard the rancidity of your oils. They will not prevent contamination by microbes.

Soleil said...

If I use another preservative, eg. Liquid germal, would that help and could I use less glycerine in that instance? I'm 100% black so my hair can't handle no more than 5% glycerine in a cosmetic formulation.

Susan Barclay-Nichols said...

Hi Soleil. I'm really confused about what you're making. It seems like you're making an anhydrous balm - one without water - to which you want to add a ton of glycerin, which is considered a water based ingredient. If you want to include it, then you have to use an emulsifier and preservative. You are now making a lotion if you do that, and this requires a lot more than just throwing a bit of this and a bit of that into a product.

I encourage you to read the newbie section of my blog to learn about your ingredients because your questions will be answered there.

I wonder why you're making an anhydrous balm instead of a conditioner for your hair? Oils do very little for our hair compared to a good conditioner, and this is true for all hair types.

If you're new to making products, don't try formulating without knowing your ingredients. Find a tried and true recipe and make that. Over time, you'll come to learn what each ingredient brings to the party and you can start making your own modifications. But you can't run before you walk.