Glycerin

Glycerin, otherwise known as glycerol, naturally occurs in the skin and has been used safely and effectively in cosmetics for more than 50 years. It provides many benefits beyond simple hydration. Glycerin keeps the skin lipids healthy, protects the skin from possible irritations, and supports the skin's barrier. Being a humectant, it attracts water into the skin and helps the skin retain moisture. Some studies have shown, such as in 2005, a connection between high quantities of glycerin in cosmetic formulations and skin hydration.
Glycerin maintains the balance of moisture between skin cells and keeps skin lipids in a liquid crystal state, important for an intact skin barrier. It normalizes the desquamation of dead skin cells in very dry skin and prevents irritation from frequent washing or harsh cleansers.
Glycerin is active even at 3% concentration, but higher concentrations yield more pronounced benefits well into the range of 20-40%. Indeed, high-concentration moisturizers with glycerin have been reported to be significantly superior compared to the low-concentration products, in particular, those in the range of 25-40% glycerin concentration. In a study involving 394 dry skin subjects, the high-concentration glycerin product not only provided immediate hydration but also yielded a long-lasting skin reservoir.
However, pure glycerin also has its drawbacks. In a 100% concentration, glycerin might pull water from deeper layers of the skin up to its surface, hence it could cause TEWL and potential dryness. The literature reports that a 25% glycerin lotion hydrates skin visibly, while nearly pure glycerin (99.7%) is not reported to have any noticeable advantages. The ideal balance for the concentration of glycerin is about 10%, which makes for a delicate balance between hydrating properties and a light, non-sticky texture, thus effectively moisturizing with barrier protection and relieving irritation.
Glycerin is much more than just a simple moisturizer; it can be strong, multi-purpose, and pivotal in maintaining skin health. Indeed, this humbly named ingredient is actually an important part of modern skincare formulation with various benefits that accrue to the skin.