1,5-Pentanediol

1,5-Pentanediol is a five-carbon diol (a molecule with two hydroxyl groups) that functions primarily as a solvent in skincare formulations. Unlike some newer ingredients, it has a longer history of use in pharmaceutical and industrial applications, including dental composites and cellulose products, before being adopted in dermatological skincare.

In topical products, this ingredient serves multiple roles: it dissolves other components, helps bind water to the skin, and can enhance the penetration of active ingredients into deeper layers of the epidermis. It is found in a small proportion of skincare products, typically at concentrations below 5%.

1,5-Pentanediol works through two primary mechanisms. As a solvent, it dissolves polar and non-polar compounds, enabling formulators to combine ingredients that might not otherwise be compatible. This is particularly useful for delivering active ingredients that are hydrophobic or have limited water solubility.

More notably, it functions as a penetration enhancer. The molecule is small enough to interact with the lipid matrix of the stratum corneum (the skin's outermost layer), creating temporary pathways that allow other ingredients to penetrate more efficiently into the epidermis. Research suggests it may be more potent at this function than some alternative diols commonly used in skincare.

1,5-Pentanediol is typically found in formulations where it serves a functional role rather than as a primary active ingredient. When present, it works in the background to improve the delivery of other actives—so its benefits are best realised when combined with other well-researched ingredients. Use products containing this ingredient as directed; there is no benefit to using higher concentrations than formulated.