Glossary
A naturally occurring glycosaminoglycan that can hold up to 1,000 times its weight in water, making it one of the most powerful humectants in skincare. Hyaluronic acid (HA) is found naturally in the skin's dermis, where it maintains hydration and plumpness. Topical HA is available in multiple molecular weights for different skin depths.
Hyaluronic acid is a polysaccharide (sugar chain) naturally present in human connective tissue, with the highest concentrations in the skin, joints, and eyes. In the skin, HA functions as a water reservoir: a single gram can bind up to 6 liters (1.5 gallons) of water. This extraordinary water-binding capacity maintains dermal hydration, creates the plump, dewy skin appearance associated with youth, and provides the gel-like matrix through which nutrients reach skin cells.
Topical HA products come in different molecular weights that determine how deeply they penetrate: High molecular weight (over 1,000 kDa): Sits on the skin surface, forming a moisture-retaining film that provides immediate hydration and plumping. Does not penetrate the stratum corneum. Medium molecular weight (100-1,000 kDa): Penetrates partially into the upper epidermis. Low molecular weight (under 100 kDa): Penetrates deeper into the epidermis, providing hydration at lower levels and stimulating the skin's own HA production. The best HA serums contain multiple molecular weights for both surface and deeper hydration.
HA is a humectant: it draws water from the environment into the skin. In humid conditions, this works beautifully. In very dry environments (low humidity, heated indoor air), HA may draw water from deeper skin layers toward the surface, potentially making dryness worse. The solution: always layer an occlusive moisturizer (beeswax balm, shea butter, or cream) over HA to seal the hydration in and prevent reverse migration.
No. HA is a humectant that attracts water but does not seal it in. Without an occlusive layer on top (moisturizer, balm, or cream), the water HA attracts can evaporate, leaving skin drier than before. Always follow HA with a moisturizer to lock in the hydration it provides.
HA is beneficial at any age. In your 20s, it provides hydration and a dewy finish. Starting in your 30s and beyond, it becomes increasingly valuable as natural HA production declines. There is no age too young or too old for hyaluronic acid; it is one of the safest and most universally beneficial skincare ingredients.
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