Propanediol, also known as 1,3-propanediol or trimethylene glycol, is a clear, colorless, and odorless liquid that has gained popularity in the skincare industry due to its multifunctional properties. This ingredient is often used as an alternative to propylene glycol, offering similar benefits with potentially fewer drawbacks [1].

One of the primary functions of propanediol in skincare is its role as a humectant. It attracts and retains moisture, helping to keep the skin hydrated and plump. This property is particularly beneficial in products designed for dry or dehydrated skin. Additionally, propanediol acts as an excellent solvent, helping to dissolve and stabilize other ingredients in the formulation, which can improve the overall efficacy of a product [2].

Research has shown that propanediol can enhance the penetration of other active ingredients into the skin. A study published in the International Journal of Cosmetic Science found that propanediol increased the skin permeation of both hydrophilic and lipophilic compounds [3]. This ability to boost ingredient delivery makes propanediol a valuable addition to formulations containing active ingredients like vitamins or antioxidants.

Moreover, propanediol has been found to have preservative-boosting properties. It can enhance the effectiveness of preservatives in cosmetic formulations, potentially allowing for the use of lower concentrations of traditional preservatives. This characteristic is particularly appealing in the current market trend towards "clean" and minimally preserved products [4].