Propanediol: What Is It & Is It Safe In Skin Care? We Investigated 

Yet, propanediol is thought to be safer and generally less irritating, so it's frequently used as an alternative in clean cosmetics. But is it actually any better? 

So, propanediol is a chain of three carbons with hydrogens, plus two alcohol groups attached. The location of each alcohol group matters, too. In this article, the propanediol we're referring to has one alcohol group on each end. That's why it's called 1,3-propanediol—because the alcohol groups are on the first and third carbons. (This info will come in handy later...promise!)

"[It] can be found in many everyday products, including moisturizers, face masks, serums, and cleansers," says board-certified dermatologist Howard Sobel, M.D. It's actually one of the most frequently used alkane diols in skin care formulations. Here's what it does:

Propanediol is an excellent solvent, which means it effectively dissolves other ingredients. And while this might sound like a negative trait, it's essential for optimal application. "As a solvent, propanediol dissolves active ingredients—like salicylic acid—for easier delivery to the skin," explains board-certified dermatologist Kiran Mian, D.O. It's also colorless, odorless, and mixes well with other ingredients, so it's useful for enhancing a formula's composition in a minimally invasive way.

Spreadability is a major factor of a good, high-quality formula. After all, if a product is too sticky and tacky, it would be an absolute pain to apply. Propanediol helps by reducing a product's viscosity, says Mian, so it can flow in a manageable way. This allows you to effortlessly move around the formula and apply it with ease.

Propanediol "also acts as a humectant and emollient," says Mian, meaning it adds moisture to the skin and reduces moisture loss. This can help improve skin texture, adds Sobel, which explains why it's found in so many personal products. The ingredient's humectant and emollient properties also make it useful in cosmetics like makeup primer, foundation, and mascara. 

Conversely, 1,3-propanediol is much gentler on the skin, explains Sobel. This makes it a great alternative for those who have developed unpleasant reactions to 1,2-propanediol. "Since it's a naturally derived ingredient, 1,3-propanediol doesn't cause much irritation or [reactions] compared to synthetic ingredients," says Sobel. It's "a generally safe ingredient that works well when used topically and mixed with other ingredients."

Although propanediol is gentler than propylene glycol, it can still cause skin sensitivity, says Mian. A 2010 study also found that the possibility of skin irritation due to propanediol is minimal. However, its overall risk for skin reactivity is low, and side effects are uncommon. It is GRAS certified ("Generally Recognized As Safe") by the United States Food and Drug Administration (FDA) and considered safe for use both as a cosmetic ingredient and for ingested food products. It's also been approved by EcoCert (an internationally recognized natural and organic seal) and the Natural Product Association (a U.S.-based natural personal care certification).

Avoid propanediol if you have a known allergy or sensitivity to the ingredient. Similarly, if you know you're sensitive to propylene glycol, it doesn't hurt to use caution with propanediol. Always do a patch test before slathering on a new product.

Propanediol is used as a solvent, viscosity reducer, humectant, and emollient. It's seldom associated with side effects, but in rare cases, it can cause irritation. If you're sensitive to propanediol (or its cousin, propylene glycol), double-check the ingredient label before using a product. On ingredient decks, propanediol may be listed as 1,3-propanediol, trimethylene glycol, or propane-1,3-diol.