Hyaluronic Acid

What the evidence says

Hyaluronic acid, also called hyaluronan, is a water-binding molecule naturally present in skin. In a leave-on serum or cream it mainly acts as a humectant, increasing water at the surface and temporarily making dry texture and fine dehydration lines look smoother. This entry covers topical skincare only; injectable hyaluronic-acid fillers are medical procedures with different benefits and risks.^[1][7]

The most repeatable benefit is hydration. In a split-face randomized trial of 76 women, several 0.1% hyaluronic-acid creams improved hydration and elasticity versus vehicle over 60 days. A separate double-blind trial in 36 older adults with dry skin found that a low-molecular-weight formulation improved skin capacitance more than high-molecular-weight hyaluronic acid or vehicle after four weeks, without a between-group difference in transepidermal water loss or symptoms.^[2][3]

Fine-line evidence is promising but less secure. The split-face trial found wrinkle-depth improvements only with its lower-molecular-weight formulas, and a small randomized study of 2-kDa hyaluronan reported shallower facial wrinkles after eight weeks. An uncontrolled 40-person serum study also recorded improved hydration and investigator-rated smoothness, but sunscreen use, the lack of a vehicle control, and testing of a complete commercial formula limit attribution to hyaluronic acid alone.^[2][4][5]

Molecular size affects behavior: Raman imaging found that 20-300 kDa hyaluronic acid crossed the stratum corneum more readily than 1,000-1,400 kDa material in the tested skin samples. That finding does not make the smallest molecule universally best. Products differ in concentration, molecular-weight distribution, vehicle, and accompanying emollients, so evidence for one formula should not be borrowed by another.^[6][1]

Topical hyaluronic acid is generally well tolerated, and a cosmetic-ingredient safety assessment considered hyaluronic acid and its sodium and potassium salts safe as used. Stinging, itching, burning, redness, or a reaction to another ingredient in the finished product can still occur. For dry skin, a hyaluronic-acid serum can be layered under a moisturizer: a randomized short-term study found that a serum-plus-cream regimen sustained hydration better than either product alone over eight hours.^[7][5][8]