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What is it - PEGs

Reviewed by Claire October 2, 2013 30 Comments

Take a look at the back of any of your favorite skin care products. Chances are that you will invariably notice a few PEGs thrown in.  But do you know why? Or why some lines tout PEG-free products as favorable to others that don’t?

A quick Google search brings up some conflicting results that need a bit of Truth in Aging perspective.

You might find, amongst others, the following phrase: “Polyethylene Glycol (PEG): Carcinogenic petroleum ingredient that reduces the skin’s natural moisture. Increases the appearance of aging and leaves you vulnerable to bacteria. Used in spray-on oven cleaners and cleansers to dissolve oil and grease.” Source.

Alarming, isn’t it? These sentiments, however, are not entirely accurate — both for its over-generalized and unsubstantiated claims, on top of several very key pieces of information that’s left out.

So, let’s get to the bottom of this.  To begin with, let me just quote a few studies to set your mind at ease:

“Overall, it is concluded, that the PEGs covered in this review are safe for use in cosmetics under the present conditions of intended use… Taking into account all the information available, it can be assumed that these compounds as presently used in cosmetic preparations will not present a risk for human health.” Source: “Safety assessment on polyethylene glycols (PEGs) and their derivatives as used in cosmetic products,” Toxicology and Preclinical Affairs, 2005.

"Studies have not shown these chemicals [propylene or the other glycols as used in cosmetics] to be carcinogens" Source: U.S. Department of Health and Human Services, within the Public Health Services Agency for Toxic Substances and Disease Registry.

So, why all the confusion? And are there any legitimate concerns about the inclusion of PEGs within your skin care products?

Yes, there are legitimate concerns about PEGs, and these include: an enhanced penetration effect, possible formula impurities, and complications for damaged skin. But before we get into that, let’s just get to know what we’re really talking about when we’re talking about PEGs.

PEGs, PEG 100s, and PEG 100 Stearates… What does it all mean?

PEG, which is the abbreviation of polyethylene glycol, is not a definitive chemical entity in itself, but rather a mixture of compounds, of polymers that have been bonded together. Polyethylene is the most common form of plastic, and when combined with glycol, it becomes a thick and sticky liquid.

In cosmetics, PEGs function in three ways: as emollients (which help soften and lubricate the skin), as emulsifiers (which help water-based and oil-based ingredients mix properly), and as vehicles that help deliver other ingredients deeper into the skin.

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 As you may have noticed, PEGs are almost always followed by a number after their name, such as PEG 100.  This number represents the approximate molecular weight of that compound.  Typically, cosmetics use PEGs with smaller molecular weights.  The lower the molecular weight, the easier it is for the compound to penetrate the skin.

Often, PEGs are connected to another molecule. You might see, for example, PEG 100 stearate as an ingredient. What this means is that the polyethylene glycol polymer with an approximate molecular weight code of 100 is attached chemically to stearic acid.

Now just to clear up a few misperceptions... PEGs are not found in anti-freeze; that's ethylene glycol, NOT polyethylene glycol.  And yes, PEGs are found in some spray-on oven cleaners, but those PEGs are quite different in both molecular weight and structure than the PEGs found in your cosmetics.

Penetration enhancing effect

The most important thing you need to know about PEGs is that they have a penetration enhancing effect, the magnitude of which is dependent upon a variety of variables. These include: both the structure and molecular weight of the PEG, other chemical constituents in the formula, and, most importantly, the overall health of the skin.

To note, independent of molecular size, PEGs of all sizes may penetrate through injured skin with compromised barrier function. So it is very important to avoid products with PEGs if your skin is not in tip top condition.

This penetration enhancing effect is important for three reasons: 1) If your skin care product contains a bunch of other undesirable ingredients, PEGs will make it easier for them to get down deep into your skin. 2) By altering the surface tension of the skin, PEGs may upset the natural moisture balance. 3) PEGs are not always pure, but often come contaminated with a host of toxic impurities.

Skin penetration enhancing effects have been shown with PEG-2 and PEG-9 stearate.

Impurities

According to a report in the International Journal of Toxicology by the Cosmetic Ingredient Review (CIR) committee, impurities found in various PEG compounds include ethylene oxide; 1,4-dioxane; polycyclic aromatic compounds; and heavy metals such as lead, iron, cobalt, nickel, cadmium, and arsenic. Many of these impurities are linked to cancer.

To draw attention to the most notable:

Ethylene oxide (found in PEG-4, PEG-7, PEG4-dilaurate, and PEG 100) is highly toxic—even in small doses—and was used in World War I nerve gas.

And then there is 1,4-dioxane (found in PEG-6, PEG-8, PEG-32, PEG-75, PEG-150, PEG-14M, and PEG-20M), which, on top of being a known carcinogen, may also combine with atmospheric oxygen to form explosive peroxides—not exactly something you want going on your face.

Responsible manufacturers do make efforts to remove these impurities, however.  So just make sure that your PEGs are coming from a respected brand.

Irritation, sensitization, and damaged skin…

Yes, PEGs may cause irritation or skin sensitization. BUT, the reasons why are usually dependent on other factors—mainly on one’s skin condition and the presence of other substances and/or medications applied simultaneously to the skin.

The main takeaway for PEGs is that they should be avoided if you have broken or damaged skin, or if they are accompanied by other undesirables in your products ingredient list.

In sum, let me just quote the final conclusions of the 2005 Toxicology and Preclinical Affairs report:

"The PEGs produce little or no ocular or dermal irritation and have extremely low acute and chronic toxicities.  They do not readily penetrate intact skin, and in view of the wide use of preparations containing PEGs, only a few case reports on sensitization reactions have been published, mostly involving patients with exposure to PEGs in meds, or following exposure to injured or chronically inflamed skin.  On healthy skin, the sensitizing potential of these compounds appear to be negative.”

There you have it.

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  • December 23, 2016

    by Amateur Chemist

    The confusion over PEG numbers has a simple answer- American companies refer to the molecular weight, Europeans count the number of PE monomer units. The numbers under 20 are monomer units, the higher numbers are molecular weights.

    MW = 18.02 + 44.05n g/mol where n is number of units


    N MW
    1 62
    2 106
    3 150
    4 194
    5 238
    6 282
    7 326
    8 370
    9 414
    10 459
    11 503

    So PEG-4 and PEG- 200 are the same things, PEG-9 and PEG-400 also match. I think molecular weight is the more reasonable method, used for thousands of other chemicals, while n-counts are specific to PEGs and give unrealistic expectations of precision. (It's difficult to make *just* n=4 PEG, you always get some 2,3,5,6 in the mix. Citing an average MW is more honest, IMHO.)

    "Standards are like toothbrushes. Everybody wants one, but nobody wants to use someone else's.

  • December 20, 2016

    by Todd

    Hi Marta but you have two conflicting replies about the number following PEG and the penetration effect.

    see below

    September 5, 2016

    by Marta

    The higher the number the lighter the molecular weight and more likely to penetrate. But really, its simpler to just avoid them,


    then on September 3, 2016

    by Marta

    Hi Buffy, we do explain the meaning of the numbers in this article. I have copied it again here for you:

    PEGs are almost always followed by a number after their name, such as PEG 100. This number represents the approximate molecular weight of that compound. Typically, cosmetics use PEGs with smaller molecular weights. The lower the molecular weight, the easier it is for the compound to penetrate the skin.

    Which is more penetration? for example a PEG 9 or PEG 40

    cheers

  • December 17, 2016

    by Estell

    Hi, ive been researching skin care ingredients and i came across this article. I was hoping you can clear something that has been confusing me.

    I read elsewhere that PEG can be "bad" for the skin in the long run, because while it moisturizes the skin by forcing moisture from deeper layers of the skin onto the surface; but never replenishing the forced out moisture.

    However, wont the other moisturizing ingredients replenish the moisture the PEG forced out? Hence, its not exactly "bad"?

    I hope im not being too simple minded about this. Thanks in advance!

  • September 5, 2016

    by Marta

    The higher the number the lighter the molecular weight and more likely to penetrate. But really, its simpler to just avoid them,

  • September 4, 2016

    by Buffy

    Thanks for answering but I'm still unclear. Is peg 10 more penetrating than 100? So 10 is worse because it is delivering into the skin more? Or do I have that backwards. I've done 5 hours of research on many chemical formulas so Im just getting confused.

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