Glycerine
Glycerin (also known as glycerol) is a polyhydric alcohol (1,2,3-propanetriol) that occurs naturally in the outermost layer of human skin (stratum corneum). It is a widely used, cost-effective humectant that has been a staple in cosmetic formulations for over 50 years. It functions not only as a moisture-binding agent but also plays roles in osmoregulation, maintenance of healthy intracellular lipid states, and skin-shedding normalization.
Glycerin attracts and retains water in the skin, with hydration benefits effective from concentrations as low as 3% and increasing up to 20–40%. Beyond simple humectancy, it helps maintain the healthy liquid-crystal state of skin lipids, supports barrier function, normalizes skin shedding in very dry skin, and protects against irritation. High-glycerin moisturizers (25–40%) have demonstrated superior and longer-lasting hydration compared to low-glycerin alternatives in a large-scale study of 394 participants.
Pure or very high concentrations of glycerin (e.g., 99.7%) are not recommended for direct skin application, as excessive humectant levels may draw water from deeper skin layers and increase trans-epidermal water loss (TEWL), potentially leaving skin drier. Optimal use is within formulated products at concentrations of approximately 3–40%.
