Is Propylene Glycol Safe for Health? An Expert Analysis

The US Food and Drug Administration (FDA) has classified propylene glycol as a substance that is 'Generally Recognized As Safe' (GRAS) for regulated use in foods, medicines, and cosmetics. This designation, however, is often overshadowed by misleading misinformation about the chemical's safety due to confusion with its highly toxic cousin, ethylene glycol.

Quick Summary

This analysis provides a comprehensive overview of propylene glycol's safety, explaining its low toxicity in approved applications for food, cosmetics, and pharmaceuticals. It clarifies misconceptions by distinguishing it from toxic ethylene glycol and addresses potential risks, such as allergies and adverse effects in vulnerable populations from excessive doses.

Key Points

• FDA deems it 'Generally Recognized As Safe' (GRAS): Propylene glycol is approved by the FDA for regulated use in food, cosmetics, and pharmaceuticals due to its low toxicity.

• Not to be confused with ethylene glycol: A common misconception arises from confusing propylene glycol with its toxic counterpart, ethylene glycol; the two have very different metabolic effects on the body.

• Metabolized and excreted quickly: The body efficiently breaks down and eliminates propylene glycol, preventing toxic accumulation under normal dietary and topical exposure.

• Risk for sensitive individuals: Allergic contact dermatitis is the most common adverse reaction and can cause skin irritation in susceptible people.

• Caution with high doses and vulnerable groups: High-dose medication, especially via intravenous administration, can pose a risk, particularly for infants, pregnant women, and individuals with liver or kidney disease.

What Is Propylene Glycol?

Propylene glycol, also known as propane-1,2-diol, is a synthetic organic compound and a type of alcohol. It is a colorless, odorless, and slightly syrupy liquid that is miscible with water. Its ability to absorb and retain moisture makes it a valuable additive across a wide array of industries. From acting as a humectant in food to a solvent in medicines, its applications are diverse and widespread.

Common Uses of Propylene Glycol

• Food and Beverage: Used as a humectant to retain moisture in items like marshmallows, coconut flakes, and baked goods; an emulsifier in salad dressings; and a solvent for flavorings and food colors.
• Cosmetics and Personal Care: Functions as a moisturizer and humectant in lotions, shampoos, and deodorants. It also acts as a solvent to help other active ingredients penetrate the skin more effectively.
• Pharmaceuticals: Serves as a solvent or carrier in many oral, injectable, and topical medications. For instance, it is used in some benzodiazepine formulations.
• Industrial: Utilized as a non-toxic antifreeze in HVAC systems, a de-icing fluid for aircraft, and a component in theatrical fog and smoke machines.

The Misinformation Around Propylene Glycol

The most significant source of public confusion regarding propylene glycol's safety stems from it being confused with ethylene glycol, a highly toxic chemical also used in antifreeze. While both compounds are glycols, their metabolic pathways and effects on the human body are fundamentally different. Ethylene glycol breaks down into toxic byproducts that can cause severe kidney damage, while propylene glycol is quickly metabolized into harmless substances. The misconception that since both are used in antifreeze, both are dangerous, is a flawed oversimplification that ignores scientific evidence.

Is Propylene Glycol Safe at Normal Exposure Levels?

For the vast majority of the population, propylene glycol is considered safe at the levels typically encountered through regulated food, cosmetic, and pharmaceutical products. When ingested, the body breaks it down into lactic acid and pyruvic acid, which are then converted into carbon dioxide and water and harmlessly excreted. The speed of this process ensures that no harmful buildup occurs under normal circumstances.

Potential Health Risks and Vulnerable Populations

While largely safe, there are specific situations where high exposure to propylene glycol can pose a health risk, primarily through medication administration or in individuals with certain health conditions.

• High-Dose Medication: In rare cases, typically involving intravenous delivery of medications, large quantities of propylene glycol can accumulate in the bloodstream, leading to metabolic acidosis and other toxic effects. This is a risk primarily in hospital settings with specific drug formulations, such as those used for lorazepam.
• Individuals with Impaired Function: People with pre-existing kidney or liver disease have a reduced ability to metabolize and excrete propylene glycol, which can lead to a buildup and potential toxicity.
• Infants and Pregnant Women: Infants, especially those under four, and pregnant women have lower levels of the enzyme needed to break down propylene glycol, making them more susceptible to toxicity from high doses found in certain medications.
• Allergies and Skin Irritation: Propylene glycol can cause contact dermatitis or irritation in sensitive individuals. This is the most common adverse reaction and can manifest as a rash, itching, or redness. The American Contact Dermatitis Society even named it the 2018 Allergen of the Year. Patch testing can help determine sensitivity.

Comparing Propylene Glycol and Ethylene Glycol

Feature	Propylene Glycol	Ethylene Glycol
Toxicity Level	Low toxicity; generally considered safe (GRAS) by the FDA for regulated food, cosmetic, and drug uses.	Highly toxic and hazardous if ingested.
Metabolism	Metabolized into harmless substances like lactic acid and pyruvic acid, which are then excreted.	Metabolized into toxic oxalic acid, which can cause kidney damage and other severe effects.
Common Uses	Humectant in food and cosmetics, solvent in medicine, non-toxic antifreeze.	Automotive antifreeze, industrial coolant, manufacturing plastics and resins.
Regulatory Status	Approved as a direct and indirect food additive by the FDA in the US.	Not permitted in food, drugs, or cosmetics due to high toxicity.
Potential Health Risks	Rare toxicity from extremely high medical doses, allergic contact dermatitis.	High risk of kidney failure, central nervous system depression, and death if ingested.

Conclusion

Scientific consensus and regulatory bodies like the FDA affirm that propylene glycol is safe for human health when used within established guidelines in food, cosmetics, and pharmaceuticals. Concerns about its safety often arise from confusion with the toxic substance ethylene glycol. While toxicity is extremely rare and typically associated with very high-dose medical applications in vulnerable populations, side effects such as allergic contact dermatitis can occur in sensitive individuals. For the average consumer, the use of propylene glycol in everyday products is not a cause for concern.

Frequently Asked Questions

Question: Is it true that propylene glycol is in antifreeze? Answer: Yes, propylene glycol is used in some non-toxic antifreeze formulations, particularly in applications where human exposure is possible, such as in RVs and marine vehicles. Ethylene glycol, which is highly toxic, is more common in automotive antifreeze.

Question: Can propylene glycol in skincare cause cancer? Answer: No, numerous studies and expert panels, including the Environmental Working Group and the National Toxicology Program, have concluded that propylene glycol does not cause cancer.

Question: What is the difference between food-grade and industrial-grade propylene glycol? Answer: Food-grade (USP-grade) propylene glycol is highly purified and meets strict standards set by pharmacopeias to ensure safety for human consumption in food, cosmetics, and medicine. Industrial-grade is less pure and used for applications like de-icing.

Question: Are there any alternatives to propylene glycol? Answer: Yes, some products use vegetable glycerin (VG) as an alternative, particularly in e-cigarettes. However, the choice often depends on the specific application, as each compound has different properties.

Question: How does the body process propylene glycol? Answer: When ingested, the body metabolizes propylene glycol into lactic and pyruvic acids, which are part of the normal metabolic process. The end products, carbon dioxide and water, are harmlessly excreted.

Question: Is it safe for pregnant women to use products with propylene glycol? Answer: While dietary amounts are safe, pregnant women and young infants should be cautious with high-dose medicinal uses, as their enzyme levels are lower for metabolizing the chemical. They are advised to consult a doctor about alternatives for specific drug treatments.

Question: How can someone tell if they have a propylene glycol allergy? Answer: An allergic reaction typically presents as contact dermatitis, with symptoms like redness, itching, or a rash. Dermatologists can perform a patch test to confirm a sensitivity to propylene glycol.

Frequently Asked Questions

Is it true that propylene glycol is in antifreeze?

Yes, propylene glycol is used in some non-toxic antifreeze formulations, particularly for RVs and marine applications where human exposure is possible. Automotive antifreeze more commonly contains highly toxic ethylene glycol.

Can propylene glycol in skincare cause cancer?

No, reputable toxicological and regulatory bodies, including the Environmental Working Group and the National Toxicology Program, have concluded that propylene glycol does not cause cancer.

What is the difference between food-grade and industrial-grade propylene glycol?

Food-grade (USP-grade) propylene glycol is highly purified and meets strict safety standards for consumption. Industrial-grade is less pure and used for non-consumer applications like de-icing.

Are there any alternatives to propylene glycol?

Yes, some products use vegetable glycerin (VG) as an alternative, such as in e-cigarettes. The best choice depends on the specific application's requirements.

How does the body process propylene glycol?

When ingested, the body metabolizes propylene glycol into lactic and pyruvic acids, which are part of normal metabolism. The final products, carbon dioxide and water, are harmlessly excreted.

Is it safe for pregnant women to use products with propylene glycol?

While typical exposure from food is safe, pregnant women and young infants should be cautious with high-dose medical uses, as they metabolize the chemical less efficiently. Consult a doctor about specific drug treatments.

How can someone tell if they have a propylene glycol allergy?

An allergy typically causes contact dermatitis, resulting in redness, itching, or a rash. A dermatologist can perform a patch test to confirm sensitivity.