What Is Propylene Glycol?
Versatile colorless, odorless substance has uses in many industries
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Medically reviewed by Mary Choy, PharmD
Propylene glycol is a non-toxic, liquid additive that absorbs water. As a humectant, emollient, and preservative, propylene glycol holds moisture while preventing mold in certain medicines, cosmetics, and foods. As a solvent, it helps improve the texture and consistency of foods, drugs, paints, and more. It is also used to create artificial smoke.
Propylene glycol is typically odorless, tasteless, and colorless, and its texture is somewhat oily or syrupy. It is generally considered a safe chemical, according to the CDC, although frequent exposure to it has been linked to skin irritation.
This article takes a closer look at propylene glycol. It covers how propylene glycol is made, what it is used for, and the side effects that may come with frequent exposure to this additive.
What Is Propylene Glycol?
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. Instead, 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 heated or shaken vigorously. Propylene glycol is generally considered safe and non-toxic by the US Food and Drug Administration (FDA).
What Is the Composition of Propylene Glycol?
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 biodiesel production. This kind of propylene glycol is mainly used for industrial purposes like making plastic or antifreeze.
How Propylene Glycol Is Used in 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 an energy source.
Unlike similar substances like ethylene glycol, propylene glycol does not form harmful crystals as it’s being broken down in the body. Amounts 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 or prevent the growth of microorganisms like bacteria and mold
As 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.
The maximum concentrations of propylene glycol are 2.5% for dairy products and 2% for all other food products.
What Else Is Propylene Glycol Used For?
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 it dissolves 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.
Related: Inactive Ingredients in Common Pain Medications
Cosmetics
Propylene glycol is a common 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 that carries out many functions in the product formulations in which it is included. 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 instrumental in skin care products for treating dry skin. Propylene glycol is an emollient because it forms an oily layer on the skin and prevents water loss.
Viscosity control: Propylene glycol reduces 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: Propelyne glycol is often used in combination with other chemicals as a preservative in cosmetic and skin care products.
Antifreeze
Propylene glycol drops the freezing point of water and water-based liquids, making it effective as an antifreeze. Propylene glycol makes up a considerable part of aircraft deicers and breaks up ice on airport runways.
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.
January 2020 UPDATE: Recent illnesses have been associated with using e-cigarettes (vaping). Since the specific causes of these lung injury cases are unknown, the Centers for Disease Control and Prevention (CDC) recommends refraining from all vaping products.
Recent studies suggest that e-cigarettes might have harmful health effects, and 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 propylene glycol is converted into cancer-causing compounds when heated up in e-cigarettes. Studies on these risks posed by e-cigarettes are still ongoing, and the risks are yet to be conclusively defined.
Related: The Health Risks of Vaping
Is Propylene Glycol Safe?
Some people may experience skin irritation or contact dermatitis from frequent exposure to propylene glycol. This exposure could be through cosmetic products, food, or topical medications.
Related: Contact Dermatitis
Summary
Propylene glycol is a versatile substance that attracts and locks in moisture and works as a preservative, making it a key ingredient in numerous foods, as well as cosmetic and skin care products. Propylene glycol is also used in drug manufacturing to dilute and stabilize medicines, as well as in e-cigarettes to mimic smoke.
Propylene glycol is generally considered safe. However, frequent exposure to it in cosmetics, foods, and topical medications has been linked to skin irritation and contact dermatitis. Additionally, some research suggests that propylene glycol may convert into cancer-causing compounds when heated up in e-cigarettes, and it is advisable to avoid e-cigarettes completely.
