Glycerin is the most used humectant in skincare, and probably the most underestimated. It doesn’t generate the same interest as hyaluronic acid or polyglutamic acid, but the research on glycerin’s skin effects is extensive and goes well beyond simple moisture attraction.
The humectant mechanism is well-established: glycerin draws water from the dermis and from the environment into the stratum corneum. But glycerin also facilitates aquaporin-3 (AQP3) water channel function – AQP3 is the primary transport pathway through which water and glycerol move between skin layers. Topical glycerin has been shown to upregulate AQP3 expression, effectively improving the skin’s own water transport infrastructure rather than simply providing an external moisture source.
In the stratum corneum’s natural moisturising factor (NMF), glycerin appears naturally – it’s produced during the breakdown of intercellular lipids as the skin sheds dead cells. This endogenous origin is likely why glycerin integrates into the skin’s moisture management system so efficiently.
At 5-10% in formulations, glycerin functions primarily as a humectant. At higher concentrations (above 30%), it starts to have an occlusive effect and can feel sticky. Most cosmetic products use 3-8%. A study published in the British Journal of Dermatology demonstrated that glycerin was as effective as hyaluronic acid for improving skin hydration and barrier function after four weeks of use.
The combination of glycerin and hyaluronic acid is better than either alone because they work at different skin depths and through partially different mechanisms. Glycerin’s additional AQP3 upregulation adds a dimension to hydration that HA doesn’t address.