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Demystifying Ingredients; The GLYCOLS / PEG

Pick up some of your skin or hair care products and chances are one of the ingredients will be a "glycol". So let's demystify the "glycols" so you will know just what they are and what they are doing in your favorite products.

So basically let's start with this. "Glycol" is the same thing as "diol" and they both mean that the chemical structure of said ingredient contains two "-OH" groups (better known as a hydroxyl group, the O is oxygen (see red molecule in image), the H is hydrogen). So what does that mean? Well, kinda nothing yet. Because there are oh so many different compounds with this double hydroxyl group. So let's narrow our focus to the ones most likely to pop up in your products. Namely, Propylene Glycol (pictured), Butylene Glycol, and the famous PEG (Polyethylene Glycol). As for the latter, we see many ingredient lists with PEG in them, so now we know that PEG is really just short for another type of glycol polymer.

What are they doing in my products?
Propylene Glycol, Butylene Glycol, and Polyethylene Glycol (PEG) are used as humectants, solubilizers, stabilizers, and to help increase product absorption into the skin. Many products have a ton of ingredients and without solubilizers/stabilizers (as well as emulsifiers, matrix creators, etc) the products would be a clumpy, non-uniform, seperated mess. Now that wouldn't sell, huh? Ok, so it's in there mostly to help the product formula come together basically, and with some added benefit of being a humectant (being able to draw in water i.e. to help moisturize) and to increase absorption.

So what's the difference?
Besides the chemical structure, not much. But what I want to cover relating to this blog, is their safety profiles. After reviewing scientific research and the MSDS data on all of these ingredients, it's pretty much safe to say, that out of all 3 listed glycols above, only propylene glycol (yes, the one used to make antifreeze) has safety concerns that are worth noting.

As far as butylene glycol and the PEGs, there really is not much data indicating any toxic or irritant potential to be concerned about. However, for propylene glycol, it's well known (at high levels) to be very toxic and certainly fatal if ingested! And remember, it is absorbed by the skin!

What does this mean?
Well, from previous posts, and ingredients in general, just because an ingredient itself has irritant/toxic potential in its purest, concentrated form, does not necessarily mean that it is not safe to use in personal products. That being said, I think it's wise to use ingredients that we know to be safer instead, hey, it's better to err on the side of caution isn't it?

Don't get all freaked out if your favorite product contains propylene glycol, there still is no reliable research showing it's not safe to use in skincare products (but also remember that this isn't easy to prove either way!). I would, however, stick to products, if given a choice, with one of the other glycols instead.

The other concern is the absorption of these ingredients. Remember, when you see these ingredients in your skincare, it means that they may actually help your skin absorb the other ingredients in the product as well. So if there's a bunch of ingredients in the product you are using that are "yucky" or you wouldn't want to be absorbed into your skin, well, than just note that their absorption can, in fact, be increased with the addition of these glycols.

Hey, remember, I can't tell you for sure whether to use certain products or ingredients all the time, just simply due to the fact that science hasn't gotten around to proving the safety/toxicity or long-term effects of many of these ingredients. But what I hope to do is just to get the thinking process started, so that we can simply be aware of what these ingredients are, their indirect/direct safety profiles, and how they work with other ingredients. After all it's all about being a wiser consumer, especially when it comes to products that you apply (and will be absorbed) by the body! Remember, if there are definitely research outcomes proving the dangers of any skincare ingredients, I will certainly try and cover them here on Truth in Skincare!


  1. Anonymous13 June, 2008

    Anti freeze in skin products . . .lol (well, maybe not a laughing matter).

  2. Anonymous17 June, 2008

    Thanks for this. I had been wondering about this for a while, especially about the propylene glycol and what the purpose of it was in skincare products.

  3. Please read this answer to a question on antifreeze from Argonne National Laboratory http://www.newton.dep.anl.gov/askasci/gen06/gen06311.htm

  4. Great Post. I think it is always best to look for ingredients that have less controversial ingredients. However, research can contantly change (as in any field), so being on top of the latest literature is always a good idea.

  5. Good information provided via post and comments also. Really appreciable post.

  6. Many people aren't aware of the toxic chemicals in our personal care and skin care. I hope the government steps up and regulate the cosmetic industry.

  7. Great Information. First of all i would love to congratulate you cause you have a lot of knowledge for skin care. Thanks for sharing

  8. Really great post. It is one of the few comments on glycols which are worth reading. Thank you!

  9. What about if these glycols are heated into a vapor? Specifically butylene, methylene or ethylene glycol. they are hair smoothing ingredients. Great article, thank you.

  10. This is really an interesting topic. Congratulations to the writer. I'm sure a lot of readers having fun reading your post. Hoping to read more post from you in the future. Thank you and God bless!


  11. As one who is allergic to propylene glycol, skin/personal care products is only the tip of the iceberg. It's in everything! Food, drinks, liquid medicine... It is harder to avoid than one might think. For me, PDO (1,3 propanediol) has been a lifesaver! While
    Propanediol and Propylene Glycol have the same Empirical Formula (C3H8O2), the molecular structure of each compound is different. Here:
    INCI name Propanediol = Chemical name 1,3 Propanediol molecular structure:


    INCI name Propylene Glycol = Chemical name 1,2 Propanediol molecular structure:




    It is the structural difference between Propanediol and Propylene Glycol that makes the two compounds distinctly different. The physical and chemical differences between Propanediol and Propylene Glycol cause the two compounds to have different toxocology profiles. Which means that there's enough of a difference chemically, that most of us with propylene glycol allergies/sensitivities, are NOT allergic to PDO! Plus there's the fact that PDO is made from corn sugar, so it takes less energy to produce (up to 35% less non- renewable energy), comes from a sustainable, renewable source & has much less of an ecological impact - both in manufacturing (40% less greenhouse gasses) & disposal *compared to propylene glycol* - makes it, to me, a much better choice than a product containing PG period. & There isn't usually a difference in price than products with PG. So I suppose it's a good price alternative ingredient to vegetable glycerin too. Even putting my allergy aside, I would choose something corn derived over something petrochemical derived any day. Reading labels on everything really sucks. It's tedious, there's junk that you can't pronounce, the print is always do damn tiny, especially on little cosmetic containers & it'll give you one hell of a headache while you're standing in the store isle comparing products for 30 minutes. BUT it is SO worth it. For your health & for the environment. Hope this helps someone as figuring it all out did for me.

    Credit to the ToxicFree Foundation for some of the info in this comment.
    PS- They have an incredibly extensive ingredient database! Especially as it pertains to cosmetics, personal care & household items. Please check out the website for in depth info and toxicity reports!


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