Propylene Glycol: The Complicated Additive with Potentially Dangerous Side Effects
Nobody likes to hear that an ingredient in antifreeze — propylene glycol — is also found in food. However, what exactly does that mean?
In recent years, there has been much frustration and confusion about the chemical compound known as propylene glycol. It’s found in literally thousands of products in various amounts, and some people claim it to be utterly harmless while others speak as if it’s responsible for devastating diseases like cancer.
The real truth about propylene glycol is a bit more complicated (like most things!). The research surrounding this substance is limited in regard to many types of cases, while it’s still a legal ingredient in many foods and other products. Read on to find out the facts.
What Is Propylene Glycol?
Propylene glycol (often referred to as PG) is the third “product” in a chemical process beginning with propene, a byproduct of fossil fuel (oil refining and natural gas processing) and also found in nature as a byproduct of fermentation. Propene is converted to propylene oxide, a volatile compound used frequently in the creation process of polyurethane plastics (and to create propylene glycol). Propylene oxide is considered a “probable carcinogen.” Finally, through a hydrolyzation process (separating molecules by the addition of water), you get propylene glycol.
A synthetic liquid substance that absorbs water, propylene glycol classified by the chemical formula C3H8O2. Propylene glycol (1, 2-propanediol) is an organic compound (a diol alcohol) and is a tasteless, odorless and colorless clear oily liquid. (1a) Another name for it is “propane-1,2-diol,” which is sometimes used when listing it as a compound on ingredient labels. As it’s found in food as an additive (in the U.S., at least), the U.S. Department of Agriculture refers to it via the E-number E1520. It’s completely soluble in water, and one major purpose it serves is as a “vehicle” for topical products, such as lotions.
Propylene glycol is found in thousands of cosmetic products as well as a large number of processed foods products. Another place you will find it is in many medications, serving as a way to help your body absorb chemicals more efficiently. It’s also a common ingredient in electronic cigarettes, contributing to taste and “smoothness” of the smoke.
This liquid substance is fraught with inconsistencies in research, as well as many differing opinions on whether propylene glycol is a dangerous toxin or a mostly harmless compound. There is no hard and fast answer to that question, however — according to a fair amount of research, the effects of propylene glycol are rarely negative and generally associated with extremely large, intravenous dosage levels.
It’s certainly less dangerous than, for example, ethylene glycol, a toxic chemical compound still used in many types of antifreeze and other household products. Ethylene glycol is considered poisonous and sometimes ingested (purposefully or by accident), requiring immediate medical attention for its toxic substances. Because of its sweet taste, ethylene glycol in antifreeze has been responsible for the deaths of many household pets who would lap it up when it collected on the ground. When propylene glycol is used in antifreeze products in place of ethylene glycol, it’s considered “non-toxic antifreeze.”
That doesn’t necessarily quell concerns, however. Many people are extremely concerned by the presence of an ingredient in antifreeze (one that’s used to deice airplanes, no less) in their food, which has sparked uproar in recent years, especially when three European countries pulled a popular alcoholic drink off the shelves for an illegal level of propylene glycol. (1b) The mix-up apparently occurred when the company sent the North American formula instead of the European formula, which contains six times less propylene glycol.
Consumers were amazed and frustrated to hear that their favorite foods and drinks might contain the chemical, exacerbated by its presence in so many other daily products. Many people became 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.
The body of research surrounding this substance is considered “fair,” according to the Environmental Working Group’s assessment. It rates propylene glycol a “3” on its health concerns scale, meaning the hazard it presents is moderately low. (2) It (correctly) designates the known issues with propylene glycol to be in the “allergies and immunotoxicity” category, with no hazard related to cancer or reproductive processes. Again, this information reflects available research.
There are a few important things to consider in our discussion on toxicity information and propylene glycol:
- It’s not “bioaccumulative.” This means that, in normal dosage or exposure levels, propylene glycol breaks down in the body within 48 hours in individuals with healthy kidney and liver function and does not accumulate over time to create toxicity in the body. (3)
- Propylene glycol is found in industrial-grade levels in products like antifreeze, polyurethane cushions, paints and the like. In food, the levels are considered pharmaceutical-grade.
- The Food and Drug Administration (FDA), in a toxicological profile, has deemed propylene glycol as “generally recognized as safe.”
- In the Centers for Disease Control and Prevention’s exhaustive report of the effects and possible toxicity of propylene glycol, no major health concerns were found. However, the organization states in the report that, “No studies were located regarding respiratory, cardiovascular, gastrointestinal, musculoskeletal, hepatic, renal, endocrine, dermal, ocular, or body weight effects in humans, or musculoskeletal, dermal, or ocular effects in animals after oral exposure to propylene glycol.” Similar statements were made about skin exposure and inhalation exposure. (4) (Nearly all the research used to support the “safety” of this chemical was done on rats, horses or monkeys — and a great deal of the points were made based on a study done on monkeys more than 60 years ago.)
The first three of these points seem to be encouraging. Although this chemical compound is not generally found in nature, it seems to be potentially safe. But what concerns me most is what is not found there — any sort of extensive human-based research on its safety.
Let’s take a look at the current research and potential effects of propylene glycol.
The Dangers of Propylene Glycol
- Skin Irritation and Allergic Reactions
One typical adverse reaction to propylene glycol includes mild skin irritation, including causing redness. Usually, this happens in people who are allergic to the chemical and subsides after a short period of time after the body has had time to break down the compound. (5)
If exposed to the eyes and facial area, propylene glycol can also be an irritant and cause mild conjunctivitis.
- Potentially Toxic to the Kidneys and Liver
Propylene glycol is used in many IV medications, including Lorazepam, an anxiety-reducing and seizure treatment medication. This drug is often administered to patients with extensive burns as sedation during the healing process or to psychiatric patients. When given Lorazepam for an extended period of time in large doses, clinicians have discovered possible kidney issues in the form of increased creatinine levels in the blood. (6) Generally, creatinine (a product of muscle breakdown and growth) remains in consistent levels in the bloodstream. Excess creatinine is a sign that the kidney is unable to process compounds at a normal rate.
People who already operate with poor kidney function are unlikely to be able to process propylene glycol efficiently and should avoid exposure when possible.
A 2007 study from the University of Connecticut assessed the treatment of propylene glycol toxicity and also noted it can be dangerous for those with liver problems. (7)
- Probably Not Safe for Infants or Pregnant Women
Prospective mothers are usually very cautious during and after pregnancy to ensure their children’s health. In the case of propylene glycol, it should be no different.
While some research states that neonates (preterm infants) have been found to have no adverse side effects from propylene glycol, it’s also true that infants cannot break down this compound as quickly as an adult can. (9, 10) This is due to the enzyme pathways that are still in development at the time of birth — depending on whom you ask, the period of development can last anywhere from six months to four years.
Before the completed growth of these enzyme pathways, parents should avoid allowing their children to ingest or be exposed to many chemicals that are potentially harmful, and pregnant mothers should do the same. (11)
- Neurological Symptoms
The one area in which the CDC’s toxicity profile negatively assessed propylene glycol was in the area of neurological symptoms. When taken orally and tested by patch test to find the amount of the chemical still in their system, a number of people were found to have varying degrees of neurological issues, including stupor, convulsions and other unspecified “severe mental symptoms.”
In a cat-based study, cats receiving the high dose developed “decreased activity, mental depression, and slight to moderate ataxia.”
It’s important here to note that the humans in the noted studies above had been exposed to orally administered medication containing propylene glycol and were most likely allergic to it.
- Cardiovascular Problems
Heart disease and symptoms have been commonly associated with propylene glycol exposure, mostly in part due to a few case studies that have caused alarming concern. One such patient was an 8-month-old who suffered a heart attack after four doses of topical medication to treat a burn.
A horse was also reported to suffer a myocardial edema after a mistaken oral dosage of a very large amount of propylene glycol.
- Respiratory Issues
There are conflicting reports regarding the impact of inhaled propylene glycol. As it’s a fairly common ingredient in smoke machines (for theater productions) and other inhalable substances, this is an important distinction to make. In rats, some scientists have found enlarged cells in the respiratory tract, as well as some nasal hemorrhaging. In another case, the horse mentioned above who suffered myocardial edema eventually died of respiratory arrest.
While the conditions under which these studies occurred are unlikely to be repeated in humans, this information is still relevant. Many substances can be potentially toxic in massive doses, and it’s impossible to guarantee these chemicals do not build up in dangerous levels, especially in some cases.
- Potentially Bioaccumulative in Certain Cases
I did mention earlier that propylene glycol is not considered bioaccumulative (builds up over time in the bloodstream). However, critically ill adults may be an exception to this rule. When administered large doses of Lorazepam, adults with or without kidney issues have experienced an abnormal buildup of propylene glycol. (12)
If you suffer from kidney or liver issues that may affect your body’s ability to process organic compounds, or are chronically ill, I highly recommend limiting your exposure to this compound as much as possible, as for these individuals propylene glycol can act like a poison.
One interesting case study followed a 24-year-old woman diagnosed with pneumonia. She was given Lorazepam for 18 days to treat her severe respiratory distress, at which time she developed lactic acidosis, a condition marked by lowering the body’s pH level to a dangerous extreme. After discontinuing the drug that poisoned her body, her condition stabilized for a period of time, but she later died after her condition deteriorated again. (13) Again, this is an example of the rare (but possible) effects of the accumulation of propylene glycol in your system.
- May Be a Pathway for More Harmful Chemicals
Perhaps the most concerning part of constant propylene glycol exposure is the way that it may provide other chemicals a free pass into your bloodstream. Propylene glycol increases your skin’s propensity to absorb whatever it comes into contact with. Considering the large amount of dangerous chemicals we encounter on a regular basis, this may be of even more danger than the compound itself.
How to Avoid Propylene Glycol
So, although propylene glycol may not be as terrifying as some people claim, it does have enough red flags to cause me to recommend avoiding it. And I’m not the only one. As a food additive, at least one study has said that it should be avoided. (14)
In order to protect your general health, hormone balance and overall chemical exposure, there are a few ways to avoid propylene glycol when possible.
- Read Food Labels
When you purchase food in a box, there’s a handy list on the side to show you what you plan to put in your body. Make use of it! Remember that propylene glycol may also be listed on labels as “propane-1,2-diol” or E1520.
- Purchase Cosmetics Free of Harmful Chemicals and Preservatives
A great number of cosmetics include propylene glycol, but in the U.S., cosmetics aren’t very well-regulated. Since ingredients do not have to appear on cosmetic products, you should purchase only from companies who list all ingredients on their packaging and don’t include propylene glycol on that list.
This isn’t just limited to makeup. Lotions and baby wipes also make the list of products that commonly contain this chemical. Other common personal care items on that list might include:
- Body wash
- Shampoos and conditioners
- Skin creams
- Baby wipes
- Avoid Processed Foods Likely to Contain Propylene Glycol
When you look at a list of foods containing propylene glycol, you’ll notice that many of them aren’t really great for you to begin with. It’s best to stick with as many unprocessed, raw or natural foods as you can.
Several common foods containing this compound include:
- Salad dressings
- Modified cornstarch
- Box cake mix
- Frozen desserts (ice cream, frozen yogurt, etc.)
- Dog and cat food (you probably won’t eat this one, but Spot will care!)
- Flavored coffee
Natural Alternatives to Propylene Glycol
Most natural alternatives to propylene glycol involve choosing foods and cosmetics free of the substance. Many of the food products containing propylene glycol don’t have “propolyne glycol-free” options unless they’re homemade.
However, feel free to use some of the recipes on my website to create homemade salad dressings and guilt-free (and chemical-free) desserts. You can also use raw butter instead of margarine for an immediate health booster to your cooking.
Because household cleaners often contain propylene glycol, I encourage you to try my Homemade House Cleaner recipe. There are a great deal of “clean” household products available, both commercially or of the DIY variety, and they will help you to greatly reduce your chemical exposure.
As electronic cigarettes also contain large amounts of propylene glycol, e-cigarette users may also try the alternative of vegetable glycerin e-cigarettes, the organic alternative — though I recommend quitting smoking entirely, of course.
Final Thoughts on Propylene Glycol
- Propylene glycol has been used for decades in a variety of products, including commercial antifreeze and plane deicing products, polyurethane cushions, paint, medicine, cosmetic products, and many types of food.
- No large bodies of research exist about the safety of propylene glycol for humans.
- Propylene glycol is considered “generally” safe by the FDA.
- Most of the time, propylene glycol does not accumulate in your body, as it breaks down within 48 hours of ingestion or exposure.
- Propylene glycol is soluble in water.
- It may cause a variety of mild to moderate side effects in humans. Rare cases suggest severe allergy to propylene glycol that could eventually (but unlikely) lead to death.
- People with liver or kidney problems, the elderly, pregnant or nursing mothers, and their infants should attempt to limit their exposure to propylene glycol.
- In order to avoid ingesting or being exposed to this substance, you should read the labels on your food and makeup, and make every effort to eat unprocessed foods regularly.
- It’s unlikely that you will experience any major adverse reactions to propylene glycol through normal exposure from food or cosmetics.
You can replace many items containing this chemical in your home with DIY or organic versions.