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What is propylene glycol?
Propylene glycol is a common chemical found in products in varying amounts. Research regarding the potential health risks of propylene glycol varies.
Propylene glycol is a common chemical found in products in varying amounts. It’s widely used in the food, cosmetic, medicine, and manufacturing industries. Research regarding the potential health risks of propylene glycol varies. Most studies have found that this chemical is toxic when taken in high doses. But food-safe glycol, which is found in the products you eat, rarely has any negative effects on human health.
Propylene glycol — commonly referred to as PG — is a petroleum-based product that’s represented by the chemical formula C3H8O2. It’s a clear, oily liquid that has no taste, no smell, and no color. It can easily absorb and dissolve in water, which is why it’s widely used in many industries.
Propylene glycol is known by many other names, including:
- Trimethyl glycol
- 1,2-dihydroxypropane
- Methyl glycol
- 1,2-propanediol
Propylene glycol is sometimes confused with ethylene glycol due to their similar properties and use as antifreeze agents. However, there’s a big difference between them. Unlike propylene glycol, ethylene glycol has high levels of toxicity, which makes it unfit for use in food products.
Where is propylene glycol used?
You can find propylene glycol in many of the products you use daily. Some among them are:
Processed foods. Propylene glycol has some useful properties, such as being able to retain moisture and dissolve a wide variety of materials. Due to these properties, it’s widely used as an additive in processed foods to improve flavor, look, texture, and shelf life. You can find this food-safe glycol in many kinds of packaged foods and drinks like cake mix, fast foods, soda, flavored coffee, popcorn, dairy products, and dried soups.
Medications. Many medications use propylene glycol because it can make it easier for your body to absorb chemicals. You can find it in oral medications, topical skin ointments like corticosteroids, and injectable drugs like diazepam and lorazepam.
Cosmetics. Due to its ability to retain moisture, propylene glycol is used as a skin-conditioning agent in various cosmetic and hygiene products. Some include soaps, shaving creams, lotions, deodorants, and shampoos.
Industrial products. Industrial-grade propylene glycol can be found in products like coolants, deicers, paints, antifreeze, and artificial smoke. It’s also commonly used in e-cigarettes, as it gives their smoke a unique taste and texture.
Is propylene glycol toxic?
Propylene glycol has very low levels of toxicity. According to the Environmental Working Group, it has a hazard score of 3, which means it presents a moderately low risk to human health. Most cases of toxicity occur when high doses of medications containing propylene glycol are given to patients over a short period.
After you eat any product containing propylene glycol, your kidneys excrete about 45% of it. Your body breaks down the rest of it and converts it into lactic acid. If this lactic acid builds up as a result of taking toxic doses of propylene glycol, it results in acidosis.
This condition prevents your body organs from working properly. If not treated in time, it can lead to kidney failure, multi-system organ failure, seizures, and even coma.
What amount of propylene glycol is safe for human use?
The US Food and Drug Administration (FDA) has given propylene glycol a “generally recognized as safe” (GRAS) status. This means it’s safe for you to eat products containing this chemical as long as you follow the recommended dietary guidelines.
According to the FDA, it’s safe for you to have about 23 mg of propylene glycol for every kg of your body weight daily if your age is between 2 and 65. However, the World Health Organization's guideline is 25 mg of propylene glycol per kg of body weight.
The amount of propylene glycol considered safe in your food will also depend on your country of residence. In the USA, where it’s used as both an indirect and direct food additive, people get around 34 mg/kg of propylene glycol daily. In contrast, the acceptable amount of propylene glycol in food is only 1 g/kg in Europe, where it is used indirectly in food products as a solvent for enzymes, colors, antioxidants, and emulsifiers.
Are there any health risks of propylene glycol?
While propylene glycol is usually safe for human use, in some cases — especially where large amounts of it are used — these side effects can occur:
Skin allergies. These are one of the most common risks of propylene glycol. The American Contact Dermatitis Society even named it the 2018 Allergen of the Year. People who take propylene glycerol-containing medications and foods can develop dermatitis — another term for skin irritation. As a result, their skin can become dry and itchy, or they can develop rashes over the face. If propylene glycol gets into the eyes, it can also lead to mild conjunctivitis (pinkeye).
Neurological problems. Various human and animal studies have shown that high doses of propylene glycol can lead to central nervous system (CNS) problems. The most common effect of its acute toxicity is CNS depression — a condition in which brain activity slows down. When used in animal studies, high doses of propylene glycol have been seen to cause loss of balance, increased breathing rate, coma, and even death. Human case studies have shown seizures and convulsions as the most common effects of propylene glycol toxicity.
Heart problems. Scientists have found no link between normal doses of food-safe glycol and heart-related symptoms in either kids or adults. However, in some cases, young kids (less than four years of age) showed symptoms like irregular heart rhythms and high blood salt levels after being given high doses of propylene glycol. Therefore, there’s less chance of adults having heart problems from this chemical as compared to very small children.
Who should not use propylene glycol-containing products?
Propylene glycol poses greater health risks for those with certain conditions. People at high risk include:
People with kidney or liver disease. It takes a healthy liver to properly break down propylene glycol and healthy kidneys to remove it from the body. If either the liver or kidneys have poor function, this process doesn’t occur efficiently. This results in lactic acid buildup, which eventually leads to kidney failure.
To prevent this problem, people with kidney and liver problems should avoid food products and drugs with propylene glycol. This is also applicable to critically ill patients, since they are likely to have poor organ function.
Young kids and pregnant women. The level of alcohol dehydrogenase — an enzyme needed for breaking down propylene glycol in your body — is particularly low in pregnant women and kids under four years of age. Therefore, there’s a high chance for people in this group to develop health problems if given propylene glycol in high doses. Infants are at particularly high risk, since their bodies can’t break down and remove this chemical as quickly as those of adults can.
Is there a treatment for propylene glycol toxicity?
The treatment for propylene glycol toxicity depends on the medical condition of the patient.
If someone gets metabolic acidosis from a glycol-containing medication, the doctor would treat them by discontinuing the drug while giving them fomepizole and sodium bicarbonate. In those cases where propylene glycol toxicity causes the blood salt levels to rise, the doctors would use hemodialysis to remove the chemical from their blood.
How to avoid propylene glycol
While the propylene glycol used in most commercial products is generally not harmful, you may still choose to avoid it to reduce the risk of future health problems.
To do so, first, check the labels of your commonly used food and cosmetic products to see if they contain this chemical. You may find it listed as propylene glycol mono and diester, E1520, 1520, or simply as propylene glycol. However, you might not find it in the ingredient list if it’s not used as a direct additive in your food.
Avoid as many processed junk foods as possible, since they usually contain food-safe glycol. Rather, make a habit of eating fresh, wholesome foods. Doing so can not only lower your chances of using glycol-containing products but also keep you healthy.
If you have an allergy to propylene glycol or a specific condition that puts you at a higher risk of acute toxicity, let your doctor or pharmacist know before you buy any medication. There’s a good chance that you’ll find a safer alternative.
