Propylene glycol is a humectant (hydrator) that can improve the supply of important active ingredients to the skin. It also plays a role in preventing formulas from melting at high heat or from freezing at low temperatures.
Also known as 1,2-propanediol, propylene glycol is used in thousands of personal care products with proven safety. As a raw material, it is a clear, purified liquid that is produced synthetically.
There are some websites that state that propylene glycol is really industrial antifreeze and that it is a strong skin sensitizer. They also point out that the Material Safety Data Sheet (MSDS) on propylene glycol warns users to avoid skin contact. As ominous as this sounds, it is far from the reality of how propylene glycol is used in cosmetic formulations.
The Cosmetic Ingredient Review Board and other groups have analyzed toxicological data and exposure studies regarding topical application of propylene glycol as commonly used in cosmetics. Their conclusion was that it is safe and does not pose a health risk to consumers. Concentrations of up to 73% have been reported with leave-on products; for rinse products, higher concentrations are allowed. https://www.paulaschoice.com/ingredient-dictionary/ingredient-propylene-glycol.html?q=Propylene%20Glycol&fdid=ingredients