Propanediol Is an Overachieving Skincare Ingredient Derms Want You to Know

Despite the fact that experts generally consider the versatile ingredient propylene glycol to be safe when used in skincare, you can't overlook the fact that it was named the American Contact Dermatitis Society's Allergen of the Year in 2018 due to its bad rap for causing contact dermatitis. If you're one of the lucky ones who experiences adverse reactions to the ingredient, like redness or itchiness, or if you're someone with eczema who could be particularly sensitive to it, you're likely on the hunt for a less irritating alternative to propylene glycol that's safer for your skin. One sub worth mentioning: propanediol.

Although the two are very similar, there are some key distinctions that could make propanediol a better option for you. To find out exactly what these differences and similarities are as well as other important characteristics to note, we interviewed board-certified dermatologist Sapna Palep, MD, of Spring Street Dermatology in NYC, and cosmetic chemist Michelle Wong, PhD, content creator at Lab Muffin Beauty Science. Together, they explain everything you need to know before making the switch from propylene glycol to propanediol in your skincare.

Keep scrolling to read all about what they have to say about the ingredients.

What Is Propanediol?

Technically speaking, propanediol is a three-carbon diol and a colorless viscous liquid that is miscible (or mixible) with water. Since it's derived from corn sugar, Palep describes propanediol as a natural alternative to propylene glycol. It can be found in cosmetics and personal care products, like lotions, cleansers, toners, and other topical skin treatments. A bit of an overachiever, propanediol can function as a solvent, humectant, and even an emollient when used in skincare.

Benefits of Propanediol for Skin

The reason you can spot propanediol on so many different product labels is due to its versatility. Although Palep says it primarily functions as a solvent, propanediol also has impressive sensory qualities and various other benefits when used in skincare:

• Dissolves ingredients: According to Palep, propanediol is considered to be an excellent solvent for harder to dissolve ingredients, like salicylic acid or ferulic acid, for instance.
• Decreases viscosity: As Palep explains it, a viscosity reducer is helpful in a variety of cosmetics, like conditioner, shampoo, foundation, mascara, body wash, hair spray, cleanser, and moisturizer, because it allows the formulas to flow well and makes them easier to use on the skin and hair.
• Improves humectancy: As a humectant hair and skin conditioner, propanediol pulls moisture into the skin and encourages water retention.
• Prevents water loss: Thanks to its emollient properties, propanediol might soften and smooth skin by reducing water loss.
• Safe for acne-prone skin: According to Palep, foam cleansers tend to use fewer surfactants (the cleansing chemicals that remove dirt and oil from your skin), which may make them ideal for acne-prone or sensitive skin types. Propanediol can increase foaming in a product, so those prone to breakouts might prefer products containing the ingredient for that reason.
• Enhances preservative efficacy: Palep adds that propanediol can also function as a preservative booster in skincare products.
• Gives the product a lightweight feel: Not only does propanediol contribute to the function of a product but also its consistency. Palep says the ingredient gives products a light texture and a non-sticky feel.

Propanediol vs. Propylene Glycol

It's easy to see how 1,2-Propanediol and 1,3-Propanediol (aka propylene glycol and propanediol, respectively) could be regularly confused for each other. The two ingredients are very similar and even share the same chemical formula; however, they have different chemical structures (as Wong explains it, the alcohol group is connected differently), which changes the way they function.

But structurally isn't the only way the ingredients differ. Palep adds that propanediol is derived from corn, while propylene glycol is derived from petrochemicals. Although propylene glycol is determined to be safe in skincare and cosmetics, propanediol is commonly used as an alternative to propylene glycol for those who want products that don't contain petroleum-based glycols. Palep points out that not enough studies exist yet to determine if it's the safer option, but studies show propanediol is likely less sensitizing and irritating to the skin.

Side Effects of Propanediol

Generally, propanediol is safe to use in skincare products for those who do not have an allergy to it. When using a new product, always patch test on a small area of the skin before applying all over your body. Palep says although there could be a small risk of irritation for some, there are no serious side effects.

How to Use It

Because propanediol has many different uses and is included in a wide variety of formulas, how it should be applied largely depends on the specific product, so use as directed by your dermatologist. But Wong adds that unless your skin is sensitive to it, propanediol is safe to incorporate into your skincare routine on a daily basis.