Glossary
A colorless, odorless, sweet-tasting sugar alcohol that is one of the most effective and well-studied humectants in skincare. Glycerin attracts water from the atmosphere and deeper skin layers into the stratum corneum, increasing skin hydration by up to 50% within hours of application. Present in most commercial moisturizers.
Glycerin is found in an estimated 75% of commercial moisturizer formulations. It is inexpensive, extremely well-tolerated, effective across all skin types, and has over 50 years of clinical data supporting its hydrating and barrier-supporting properties. Despite lacking the marketing appeal of newer ingredients, glycerin consistently outperforms most trendy humectants in head-to-head clinical studies.
Glycerin is a trihydric alcohol (three hydroxyl groups) that forms hydrogen bonds with water molecules, pulling moisture from the atmosphere (in humid conditions) and from the dermis (in dry conditions) into the stratum corneum. Applied at 5 to 20% concentration, glycerin increases stratum corneum hydration by 30 to 50% within hours. It also integrates into the lipid lamellae between corneocytes, improving the ordered lipid structure that maintains barrier function.
Both are humectants, but they work differently. Glycerin is a small molecule that penetrates into the stratum corneum and works from within; hyaluronic acid is a large polymer that primarily works on the surface (high molecular weight HA) or in the upper epidermis (low molecular weight HA). Clinical studies suggest glycerin provides more sustained, longer-lasting hydration than hyaluronic acid when both are formulated at effective concentrations. However, HA provides more immediate plumping and a more luxurious sensory experience.
5 to 20% provides optimal hydration without stickiness. Above 20%, glycerin becomes tacky and can actually pull too much water from the dermis in very dry environments. Most well-formulated moisturizers contain 5 to 15% glycerin. Pure vegetable glycerin should be diluted before facial use. A 10% glycerin solution in water or mixed into your moisturizer provides excellent hydration.
Glycerin is one of the most universally tolerated skincare ingredients. It is non-comedogenic, non-irritating, and suitable for dry, oily, sensitive, acne-prone, and aging skin. Allergic reactions are extremely rare. It is safe during pregnancy and nursing. There are virtually no skin types or conditions for which glycerin is contraindicated.
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