Hyaluronic Acid
Hyaluronic acid (HA) is a large sugar polymer (molecular weight up to 4 million Dalton) found naturally in the human body, with roughly half of the body's ~15 g residing in the skin. It is the most dominant molecule in the extracellular matrix between skin cells. Different molecular weight versions exist — high (>500 kDa), low (<500 kDa), and ultra-low (<50 kDa) — each with distinct behavior when applied topically.
HA can bind up to 1,000 times its own weight in water, making it an exceptional surface hydrator and skin protectant. High-molecular-weight HA forms a protective barrier on the skin surface and can act as an osmotic pump to help water-soluble actives penetrate deeper. Low-molecular-weight HA (≥50 kDa) may hydrate slightly deeper into the epidermis, support skin self-defense, and has shown benefit in inflammation-related conditions such as rosacea and seborrheic dermatitis.
Ultra-low molecular weight HA (<50 kDa, particularly ~20 kDa) has shown potential pro-inflammatory activity in reconstituted human epidermis models; cautious users may wish to avoid ultra-low MW versions. The INCI name alone does not reveal molecular weight, so the specific form in a product cannot be determined from the ingredient list.
