The sobering truth about propylene glycol and its safety in food and cosmetics

Headlines such as “What’s so terrible about propylene glycol?” and “Propylene Glycol: Antifreeze in cosmetics?” do not paint a pretty picture about this shady-sounding substance. It’s perfectly understandable if they make you question propylene glycol and any products that contain it.

But this is just another unjustified witch hunt on a common and safe ingredient. Safe not because we say so, but because it’s been proven to be safe by relevant institutions, highly regarded scientists and numerous studies.

The purpose of this article is to give you a scientifically backed, objective and realistic assessment of propylene glycol’s safety. The material for this piece was gathered from relevant institutions and peer reviewed studies; the article was written by a pharmacist, and all of the third-party references can be found at the bottom of the page.

In short, don’t take our word for it – trust the scientists who have no personal interest in spreading panic and misinformation.

The groundwork: Basic information on propylene glycol

Propylene glycol is a clear, colourless and viscous liquid with a very mild, sweet taste. It’s good at dissolving water-soluble substances and is excellent in retaining moisture. That is one of the main reasons why it can be found in thousands of products, including foods, medicine and cosmetics.

Propylene glycol is commonly used in:

• Food (drink mixes, soft drinks, salad dressings, instant soups, cake mixes, food colouring, grated cheese, fast foods, bread, marshmallows, coconut flakes, nuts, dairy products, etc.);
• Tobacco products;
• Oral, intravenous and topical pharmaceuticals (such as phenytoin, diazepam, and lorazepam);
• Cosmetics (liquid foundations, skin moisturisers, shampoos, hair conditioners, lipsticks, etc.);
• Many other products for general use (deicers, antifreeze*, hydraulic fluids, smoke simulators, etc.).

* Just because an ingredient is in antifreeze doesn’t mean that it’s toxic. After all, water is in antifreeze too.

One possible reason why propylene glycol has gained such a bad reputation is because it can be mixed up with its cousin, ethylene glycol. Both of these alcohols have been used in antifreeze thanks to their low freezing points, but they are very different substances.

While propylene glycol is safe to use in food, medicine and cosmetics, ethylene glycol is highly toxic for humans and is never used in similar products.

The role of propylene glycol in cosmetic products

When used in cosmetics, propylene glycol usually has one of several possible roles:

• It retains water on the skin. This ingredient is very good at drawing water, so when applied to the skin it helps its rehydration.
• By retaining water on the skin’s surface, it also helps renew its protective barrier, which is especially helpful with skin conditions that are caused by a damaged protective layer, such as eczema.
• It also retains water in the product itself, giving it a desired consistency and making it last longer.
• Propylene glycol enhances active ingredients in a cosmetic product by allowing them to better penetrate the superficial layer of the skin. That way it makes skin care products more effective.

What happens to propylene glycol when we eat it?

When we eat propylene glycol in some of the foods mentioned above, just under half of it (45%) gets excreted by the kidneys completely unchanged.

The rest of it is metabolised in the liver and turned into lactic acid, and then into pyruvic acid. These metabolites are the usual components of one of the staple metabolic processes in the human body – the citric acid cycle – and are finally metabolised further into carbon dioxide (CO₂) and water. Carbon dioxide gets exhaled, and extra water is released through urine.

In other words, very quickly after ingesting it there is no trace of propylene glycol left in our bodies.

The official judgment on propylene glycol’s safety

Propylene glycol was given the GRAS mark by the U.S. Food and Drug Administration (FDA 2017), which means it is “generally recognized as safe”. FDA further sets the safe average daily dietary intake at 23 mg/kg of body weight for everyone from 2 to 65 years of age (ATSDR 2008).

It is also recognised as safe and nontoxic by other major organisations such as:

• Cosmetic Ingredient Review Expert Panel,
• The European Pharmacopoeia,
• European Regulation (EC) No 1333/2008 (as food additive) and Regulation (EC) No 1223/2009 (as a cosmetic ingredient),
• United States Environmental Protection Agency (USEPA),
• National Toxicology Program (NTP) by the US Department of Health and Human Services,
• The Agency for Toxic Substances and Disease Registry (ATSDR),
• Organisation for Economic Cooperation and Development (OECD),
• Canadian Centre for Occupational Health and Safety,
• The Environmental Working Group (EWG), and others.

The common conclusion for all of these reputable institutions is that propylene glycol is non-toxic, non-carcinogenic, that it doesn’t damage genes, affect fertility or reproduction.

Cosmetic Ingredient Review has further stated that it is safe for use in cosmetics, and clinical data showed that is is safe to be used in cosmetic products at concentrations up to 50% (which is much higher than what is usually the case with these kinds of products).

Recorded propylene glycol side effects

The only adverse effects of propylene glycol toxicity were a result of improper use, such as heavy use of injectable medicines, or prolonged use on burned skin. When it comes to ingesting propylene glycol, there have only been a couple of poisoning cases – one of a man who drank large amount of cinnamon whiskey (most of his symptoms were attributed to alcohol (ethanol) poisoning, but some of them could have been caused by propylene glycol) and one where a man drank the liquid inside the ice packs.

Other than these excessive consumption cases and occasional allergies, there have been no other reported cases of toxic effects caused by propylene glycol.

To put things into perspective, the median lethal dose or propylene glycol in rats is 9 grams per pound or 20 g/kg (that is the dose that is expected to kill an average rat). Compare this to sugar with its lethal dose determined to be 13.5 grams per pound (or 29.7 g/kg), or salt, which is only 1.4 grams per pound (or 3 g/kg).

One word of caution goes out to people who are allergic to propylene glycol. Just like with any other ingredient, a small percentage of people will be allergic to this substance and people with sensitive skin and other confirmed allergies are more prone to it than others. In these cases applying propylene glycol to the face or mucous membranes can cause irritation, rash, redness and itching. If you are allergic to it and you ingest it through food or have it administered intravenously with medicine, you may develop systemic dermatitis.

To avoid this issue, always test every new product that is applied to the skin. If you have no reaction within 24 hours, you are most likely safe to continue using that product as it is intended.

Don’t trust the headlines without looking into the data

This is the only appropriate conclusion we can give you and it doesn’t only relate to propylene glycol, but also to many other skin care and food ingredients that have been proclaimed as public enemies without valid scientific backing.

When looking at such sensationalistic claims (and even when reading boasting marketing materials) always look into the data yourself. If the references quoted are company’s own website, studies funded by the brand or, even worse, if there are no references at all, it is worth double checking the information through a more reputable source. Today, thankfully, those kinds of checks are easily available and only a few clicks away.

References:

• Agency for toxic substances and disease registry
• Safety assessment of propylene glycol, tripropylene glycol, and PPGs as used in cosmetics, Monice M Fiume 1, Wilma F Bergfeld, Donald V Belsito, Ronald A Hill, Curtis D Klaassen, Daniel Liebler, James G Marks Jr, Ronald C Shank, Thomas J Slaga, Paul W Snyder, F Alan Andersen, Int J Toxicol. Sep-Oct 2012;31(5 Suppl):245S-60S. doi: 10.1177/1091581812461381. 
• A toxicological review of the propylene glycols, Jeff R Fowles 1, Marcy I Banton, Lynn H Pottenger, Crit Rev Toxicol. 2013 Apr;43(4):363-90. doi: 10.3109/10408444.2013.792328
• EWG’s Skin Deep
• CIR (Cosmetic Ingredient Review) 2006. Amended Safety Assessment of PEG Propylene Glycol Derivatives as Used in Cosmetics
• Final Report on the Safety Assessment of Propylene Glycol and Polypropylene Glycols, Journal of the American College of Toxicology, Volume: 13 issue: 6, page(s): 437-491 Issue published: December 1, 1994