Glycerin is one of the most widely used humectants in skincare — a humectant being an ingredient that attracts and binds water. It draws water both from the environment and from deeper skin layers, supporting the stratum corneum's moisture content.
It is widely used because it is well tolerated, compatible with many formulations and has a long-established safety profile. It often appears high on INCI lists, as most formulas contain a meaningful proportion.
Humectants alone are not enough: the water they attract needs a supported barrier to stay in. A good formula therefore pairs humectants like glycerin with skin-identical lipids — one brings water, the other keeps it in.