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  • Writer's pictureThe Pink Elephant Lady

Chemical of the Day: Propylene Glycol

I'm starting a new feature in my blog called "Chemical of the Day". Each time we'll focus on a different ingredient commonly used in personal care and cleaning products and attempt to separate facts from viral Internet memes. Today we'll focus on propylene glycol, with a side discussion of margarine!

You've probably seen lots of mommy bloggers and 'natural news' websites proclaiming loudly that "Propylene Glycol is antifreeze!" Some of these are the same folks that have also declared "Margarine is one molecule away from plastic!" Both of these statements have some truth to them, but are unnecessarily alarmist (and both are good examples of the 'guilt by association' logical fallacy - remember that Logic class back in college when you learned about all the bad argument techniques?) But I digress.....

We don't use propylene glycol in any of our products. So, this blog post is not going to be simply a defense of this ingredient. And I'm not saying propylene glycol or margarine are totally safe or unsafe - we're going to explore that issue here in detail. I'm just saying that those 'antifreeze' and 'plastic' phrases sound like nails on a chalkboard to me (like when I hear companies say their product is "chemical free" - and then I silently picture the chemical formulas for all of their products' ingredients in my head might look like).

A good deal of the information that goes viral regarding product ingredients represents a lack of understanding of basic scientific principles. On the other hand, I also don't support the notion that it's somehow anti-science to question the safety of the products we use everyday. (Note on the image below: well, ALMOST everything is made of chemicals. Energy itself isn’t a chemical. Light waves and sound waves (both forms of energy), heat, electricity, and magnetic fields aren’t chemicals. Subatomic particles – like protons, neutrons, electrons and crazy things like the Higgs boson would not traditionally be called chemicals. But everything else? Yeah, it's all chemicals! And all those other things I mentioned couldn't exist without chemicals!)


Hmmm....not really. Think about it this way: water (H2O) is also just one oxygen atom away from being hydrogen peroxide (H202) - and mixing concentrated hydrogen peroxide (CHP) with a fuel can create a liquid explosive . So, should we now avoid water, and make a meme stating that "Water is just one atom away from an ingredient used in making bombs"? And did you know that the air we breathe everyday contains ingredients that can be used to run a car? Sounds so scary! Yup, hydrogen and oxygen are components of fuel cell technology.

Bottom line is, saying that one substance is "one molecule away" from another substance doesn't really tell us ANYTHING, because that one molecule makes a whole world of difference. "Adding" another molecule to margarine does not turn it into plastic. Many substances share similar chemical properties but even the smallest variation in their chemical formulas can set them a world apart in terms of what they are. Remember the old rhyme, "Johnny was a chemist. Johnny is no more. For what he thought was H2O was H2SO4." Poor Johnny! In his defense, sulfuric acid DOES look very similar to water.

To have a conversation about margarine that makes sense, we need to talk about partially hydrogenated oils, trans fats, and unsaturated fats. Non-hydrogenated, trans fat-free soft margarine is now widely available, made from vegetable oils such as canola, olive, soybean and safflower, and have a different make up than margarines in the past. But I'm not going to get into whether or not margarine is a health food, or whether or not it's a better option than butter, or a discussion of the Paleo diet, veganism, or whether it's more the sugar and simple carbs or the animal fat in American diets that's giving us so many ill health effects that can only be described as "Affluenza" - perhaps I'll save that for another blog post!


Oh, wait - I was supposed to be talking about propylene glycol! Back to that. Propylene glycol is a petroleum-derived, colorless organic liquid that's manufactured by treating propylene with chlorinated water to form chlorohydrin, which is then converted to the glycol, an alcohol, by treating it with a sodium carbonate solution. (By the way, in chemistry, 'organic' means chemical compounds with carbon in them, NOT 'grown without synthetic pesticides').

And yes, propylene glycol IS an antifreeze ingredient. Propylene glycol is considerably less toxic than ethylene glycol and can be labeled as "non-toxic antifreeze". It is used as antifreeze where ethylene glycol would be inappropriate, such as in food-processing systems or in water pipes in homes where accidental ingestion by pets or children may be possible. The FDA allows propylene glycol to be added to many processed foods, including ice cream, frozen custard, salad dressings, and baked goods, and it is commonly used as the main ingredient in the liquid used in e-cigarettes. The Contact Dermatitis Institute has a long list of consumer products that contain propylene glycol (, from infant wipes to sunscreens to mascara.

The fact that propylene glycol is an antifreeze in and of itself doesn't mean it's dangerous (and maybe it IS dangerous - but not because the meme says, "It's antifreeze!") 'Antifreeze' is exactly that - two words, ANTI and FREEZE, as it lowers the freezing point of a water-based liquid and increases its boiling point. Kind of like salt. Salt also lowers the freezing point of water, and since ice is water in its solid state, that's why municipalities use salt on the roads. While salt is frequently used for de-icing, salt is NOT used for cooling systems because they can cause severe corrosion to metals (hence the rust on the underbelly of cars in colder U.S. states). However, saying propylene glycol is dangerous because it's antifreeze is akin to saying salt is dangerous because it's sprinkled on the roads. Both are essentially 'anti-freeze', to a certain degree. A (relatively) safe ingredient like propylene glycol or salt can be used in a way that sounds like it means the chemical is dangerous. If I use vinegar in the rinse compartment of my dish washing machine, that doesn't mean I should post a meme about people using dishwasher rinse agent on their salads!

Bottom line? Many people are scared of the association between antifreeze and food, although propylene glycol simply lowers the freezing point of water (just like salt) and was only introduced into antifreeze products to replace a more dangerous chemical.


According to EWG, the body of research surrounding this substance is considered fair, and it rates propylene glycol a “3” on its health concerns scale, meaning the hazard it presents is moderately low, and it designates the known issues with propylene glycol to be in the “allergies and immunotoxicity” category, with no hazard related to cancer or reproductive processes.

The Cosmetic Ingredient Review notes (CIR) that propylene glycol is used as "penetration enhancer". Some ingredients in personal care products are only considered safe because they are not absorbed into the skin, and if propylene glycol enhances absorption of such products, they should not exist together in formulations. However, the CIR concludes that propylene glycol presents no major concerns and is safe when used in the amounts indicated in their report. Take note of the following, though: the CIR is funded by the Personal Care Products Council, which is the government lobbying arm/trade association of the personal care products industry. Personal care products are not subject to the same rigorous premarket testing requirements as prescription and over the counter drugs. The industry essentially regulates itself through the safety data it publishes via CIR.

I'm always concerned that even as we are assured that 'the dose makes the poison', and that potentially toxic ingredients are in such minute quantities so as to be rendered benign, there are no long-term studies showing that chronic, low-dose exposure over many years is safe. A 1972 study published in Food and Cosmetic Toxicology (now renamed Food and Chemical Toxicology) is as follows:

" Groups of 30 male and 30 female weanling rats were fed for 2 years on diets containing 0 (control), 6250, 12,500, 25,000 or 50,000 ppm (parts per million) of propylene glycol. The treatments were found to have no effect on mortality, body-weight gain, food consumption, haematology, urinary cell excretion, the urine-concentrating ability of the kidneys, organ weights or pathological findings, including the tumour incidence. In a parallel short-term study in groups of 15 males and 15 females fed 0 or 50,000 ppm propylene glycol in the diet for 15 wk, haematological indices, serum and urine analyses and organ weights were again found to be comparable in the control and test groups. No carcinogenic potential was detected with dietary levels of propylene glycol up to 50,000 ppm, which was also established as the no-untoward-effect level in this study. This level is equivalent to an intake of approximately 2·5 g/kg/da "


Propanediol is considered to be an alternative ingredient to propylene glycol. Some allergy doctors/dermatologists tell their patients with allergies to propylene glycol that one is just is another name for the other. However, there are some notable differences. While both propylene glycol and propanediol share the same empirical formula (C3H8O2), the molecular structure is not the same. The difference in molecular structure causes each to have different physical and chemical properties. The different chemical and physical properties result in different toxicology profiles.

Propanediol is mainly derived from a sustainable and renewable corn sugar fermentation process, while propylene glycol is mainly synthesized from a petrochemical. Propanediol has a lower potential to irritate or sensitize skin than propylene glycol.

There is some concern from consumers about insecticides, herbicides, and GMO corn being used in the production of propanediol (remember, however, that propylene glycol is a petroleum derivitive, so it's kind of like 6 of one, half dozen of the other!) And of course, propanediol is more expensive that its petroleum-based cousin.


I think the main concern about propylene glycol is that some consumers with sensitivity to it will have adverse skin reactions. However, there does not seem to be solid scientific evidence for all of the other maladies associated with propylene glycol on the internet. As far as e-cigarettes and many of the processed foods that contain propylene glycol, there are already health concerns about them aside from the PG. There is, of course, the concern that the product is a petroleum derivative. But keep in mind, most personal care products are packaged in petroleum-derived plastics.

I can understand how consumers may not trust safety studies funded by a trade association representing huge companies who are selling the products containing the chemicals being studied.

As consumers increasingly question the ingredients in the products they use, more information (both reliable AND off the wall) is going viral about these ingredients. Unfortunately, information most easily found, spread, and understood by consumers may or may not be accurate or even science based. Negative press and consumer demand is making propylene glycol less desirable. Some companies are phasing out propylene glycol when creating their formulas because of the concerns raised by customers. When it comes to selling products, consumer perception rules.


"Safety Assessement of Propylene Glycol", Personal Care Products Council:

EWG Skin Deep Cosmetics Database:

Snopes, Butter vs. Margarine:

Truth in Aging: Propylene Glycol.

Contact Dermatitis Institute: Propylene Glycol.

The Toxic Free Foundation Ingredient Database: Propylene Glycol.

Food and Cosmetic Toxicology: Long term Toxicology of Propylene Glycol in Rats


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