What Is Propylene Glycol?

Propylene glycol is a synthetic liquid that’s used for a variety of purposes in the pharmaceutical, cosmetics, food and manufacturing industries. It is typically odorless, tasteless, and colorless and its texture is somewhat oily or syrupy.

What It Is

Propylene glycol is an alcohol that absorbs water and mixes completely with many solvents. While you might see propylene glycol described as an organic compound, this does not mean it’s naturally occurring. Rather the term organic compound refers to the fact that it contains carbon.

While it’s a liquid, propylene glycol can become vapor in the air when it is heated or shaken vigorously. Propylene glycol is generally considered safe and non-toxic by the US Food and Drug Administration (FDA). 

Composition

Propylene glycol can be created in two different ways. It is primarily made by treating propylene oxide—a chemical produced from refining petroleum—with water.

Propylene glycol can also be obtained from glycerol, a major byproduct of the biodiesel production process. This kind of propylene glycol is mainly used for industrial purposes like making plastic or antifreeze. 

Uses

Propylene glycol is used in a variety of products and manufacturing processes.

Pharmaceuticals

Propylene glycol is widely used as a solvent in drug manufacturing. This means that it’s used to dissolve other substances (usually solid) without changing their fundamental structure or composition.

Propylene glycol is also used as a carrier in drug formulations. Active ingredients can be formulated in it and delivered to the body through it. Finally, it is used to dilute and stabilize medicines.

Propylene glycol can be used in different forms of drugs including oral drugs like capsules and tablets, topical drugs like creams and gels, and intravenous (injected) drugs.

Cosmetics

Propylene glycol is a commonly found ingredient in cosmetic, personal, and skin care products. It is in anywhere from 26.4% to 37.8% of registered personal care products. Propylene glycol is a versatile substance and carries out many functions in the product formulations its included in. Some of these functions are:

• Humectant: Humectants are included in cosmetic and skin care products for their moisturizing abilities. Propylene glycol works as a humectant by attracting moisture to the skin, and consequently hydrating and moisturizing it.
• Solvent: Propylene glycol is used to dissolve substances in a product formulation to get them to mix and work together properly. It also acts as the carrier for active ingredients. 
• Emollient: Emollients are ingredients that soothe and hydrate the skin. They’re very useful in skin care products for treating dry skin. Propylene glycol is used as an emollient because it forms an oily layer on the skin, and prevents water loss.
• Viscosity control: Propylene glycol is used to reduce the thickness of cosmetic formulations and products. This helps them spread across the skin better, and it also improves how well the products are absorbed. 
• Preservative: Porpelyne glycol is often used in combination with other chemicals as a preservative in cosmetic and skin care products.

Food

The use of propylene glycol in foods is common and generally considered to be safe. When consumed, propylene glycol breaks down in the body quite quickly —within 48 hours—and is changed to a source of energy.

Unlike similar substances like ethylene glycol, propylene glycol does not form harmful crystals as it’s being broken down in the body. Amounts of it that are not broken down and metabolized are passed out of the body in urine.

Some of the ways propylene glycol is used in food include:

• As an anticaking agent, helping to prevent lumps from forming in food
• As a solvent in food flavorings, helping to dissolve and mix ingredients in them.
• As a dough strengthener
• To improve flavors in food
• As a preservative, its antimicrobial properties help to kill and/or prevent the growth of microorganisms like bacteria and mold
• A s a food thickener
• To help retain moisture in food

Propylene glycol is safe for consumption and the FDA approves its use in food at certain concentrations. It may form up to 97% of the contents of seasonings and flavorings, 24% of confections and frosting, and 5% of alcoholic beverages and nuts/nut products

For dairy products and all other food products, the maximum concentrations of propylene glycol are 2.5%, and 2% respectively. 

Antifreeze

Propylene glycol drops the freezing point of water and water-based liquids, making it effective as an antifreeze. Propylene glycol makes up a huge part of aircraft deicers, and it's also used to break up ice on runways in airports.

Because propylene glycol is non-toxic, it’s also often used as an antifreeze in food processing systems and in water pipes that lead to connecting hoses.

Electronic Cigarettes

Alongside vegetable glycerin, propylene glycol is the major ingredient in the liquids (e-liquids) used in e-cigarettes. To mimic smoke, propylene glycol is converted to extremely tiny droplets by e-cigarettes. It also functions as a carrier for nicotine and flavorings which are added to some e-liquids.

Recent studies suggest that the use of e-cigarettes might have harmful health effects, and that some of these effects may be linked to the mixture of propylene glycol and other ingredients. Some of these health risks include lung damage and lung disease.

Other studies also indicate that propylene glycol is converted into cancer-causing compounds when it’s heated up in the e-cigarettes. Studies on these risks posed by e-cigarettes are still ongoing and the risks are yet to be conclusively defined.

Risks

Some people may experience skin irritation or develop contact dermatitis from frequent exposure to propylene glycol. This exposure could be through cosmetic products. food, or topical medications.

A Word From Verywell

Propylene glycol is a synthetic substance with a myriad of uses in the industrial, pharmaceutical, food, and cosmetics industries. At the levels that people typically consume or are exposed to it, propylene glycol is safe and non-toxic.