Hyaluronic acid (INCI: Sodium Hyaluronate or Hyaluronic Acid) occurs naturally in the body, particularly in the dermis and connective tissue. In skincare it is used as a humectant with high water-binding capacity, to support the skin's moisture appearance.
Products use different molecular weights. Higher-weight forms stay more on the surface, creating a film-like feel; lower-weight forms distribute more within the stratum corneum. Many formulas combine several sizes.
A practical note: hyaluronic acid attracts water, so used alone in very dry environments it may not deliver expected comfort. Best results usually come when a barrier-supported moisturiser is applied over it.