Propanediol is a naturally derived ingredient that is used in cosmetics and personal care products as an emollient, humectant, and solvent.
Propanediol is a glycol with the chemical formula C3H8O2. It exists in two different forms: 1,2-propanediol (also known as propylene glycol) and 1,3-propanediol. The structural difference between these two compounds is the relative positions of alcohol groups. While this difference may be subtle, it results in differing properties and required safety measures for these two compounds. For the purposes of this article, the term “propanediol” will refer to 1,3-propanediol.
Propylene glycol is a synthetic product obtained from the hydration of propylene oxide, which comes from petroleum products. While propanediol can be produced from propylene oxide as well, it can also be naturally derived from corn. The process begins with drying the harvested kernels, which are then soaked in hot water and mild acid to soften the corn’s shell. Next, the starch is separated from the protein. Sugar obtained from the starch is the raw material for the propanediol. A microorganism is introduced to the corn sugar for fermentation. Once the fermentation is complete, the propanediol is purified and refined.
Since propanediol can be produced from a natural source, it is used as an alternative to petroleum-derived glycols. The process of making propanediol from corn is more energy efficient than conventional petrochemical processes. It produces a smaller environmental footprint, requires lower operating costs, and has greater sustainability due to use of renewable corn feedstock. Thus, propanediol is an appealing ingredient for companies that produce natural and “green” personal care products.
In cosmetics and personal care products, propanediol functions as an emollient, humectant, and solvent.
As an emollient, propanediol has the ability to soften and soothe the skin. Upon application, propanediol forms an occlusive film on the surface of skin that aids in preventing water loss. Over time, this increases skin hydration by causing buildup of water in the stratum corneum (the uppermost layer of skin). Products that contain propanediol, such as creams, lotions, and other moisturizers, are an excellent choice for dry skin conditions.
Propanediol also functions as a humectant. A humectant is a hygroscopic substance that often has a molecular structure with several hydrophilic groups. This structure allows humectants to attract and retain the moisture in the air nearby via absorption, drawing the water vapor into or beneath the surface. Once again, these properties make propanediol an ideal ingredient for dry or dehydrated skin.
Those with aging skin can also benefit from humectants since the skin naturally loses hydration with age. As part of the normal aging process, there is a significant decrease in the amount of NMF (Natural Moisturizing Factor) found within the epidermis. The NMF is comprised of natural humectants, as well as amino acids, PCA, lactates, sugars, salts, urea, and peptides. All of these substances work together to keep the skin’s surface intact, supple, and hydrated. When the NMF becomes depleted, the skin appears dry and flaky, and is more susceptible to wrinkle formation. Applying products that contain humectants like propanediol can keep skin hydrated while working to reduce signs of aging.
These same hydrating properties of propanediol make it a useful ingredient for hair care products, such as shampoo, conditioner, leave on conditioners, or styling aids. It provides a cleaner feeling after rinsing while increasing moisturization, improving detangling, reducing static, and improving wet and dry combing.
Lastly, propanediol functions as a solvent. It is considered to be an excellent solvent for harder to dissolve ingredients, such as salicylic acid, ferulic acid, allantoin, and ascorbic acid. Propanediol provides a light, non-sticky, slightly dry skin feel.
Propanediol is considered a safe and appropriate ingredient not only for cosmetic products, but also for ingested food products. Propanediol is GRAS certified (“Generally Recognized As Safe”) by the United States Food and Drug Administration (FDA). In addition, propanediol has approval from EcoCert (an international recognized natural and organic seal) and the Natural Product Association (US based natural personal care certification). In two independent human skin patch tests, propanediol at concentrations as high as 75% did not produce skin irritation or sensitization reactions. The Cosmetic Ingredient Review (CIR) Expert Panel has not assessed the safety of propanediol.
References: Truth In Aging, “Propanediol”, Wikipedia, “Bioseparation of 1,3-propanediol”, LotionCrafter, “Propanediol 1,3”, DuPont, “Zemea in Cosmetics & Personal Care”.