What Is Hyaluronic Acid?
Hyaluronic acid (HA) is a glycosaminoglycan — a long-chain polysaccharide — that occurs naturally throughout the human body, with the highest concentrations in the skin, joints, and eyes. In the dermis, HA is a major component of the extracellular matrix, contributing to tissue hydration, volume, and structural support. It is capable of binding up to 1000 times its own weight in water, making it the most powerful natural hydration molecule in the body. Skin naturally produces HA, but this production declines significantly with age.
Molecular Weight and Penetration
Topical HA products vary dramatically in their molecular weight, which determines depth of action. High molecular weight HA (above ~1000 kDa) remains on the skin surface, forming a moisture-retaining film and providing immediate plumping of the skin surface. Low molecular weight HA (below ~50 kDa) can penetrate deeper into the epidermis. Very low molecular weight HA (sodium hyaluronate, ~5kDa fragments) may reach the upper dermis. Multi-weight formulas address multiple skin layers simultaneously.
How to Apply HA Effectively
Apply to damp skin immediately after cleansing or misting. This gives the HA moisture to bind to and draw into the skin rather than pulling from deeper layers. Always follow with a moisturiser containing emollients and occlusives to prevent the attracted moisture from re-evaporating — especially critical in low-humidity environments.
Common misconception: Hyaluronic acid does not "deeply penetrate" skin in typical formulations. Most topical HA acts at the skin's surface and upper epidermis — which is still highly effective for hydration and fine line reduction, just not dermal remodelling.
See Hyaluronic Acid Deep Dive and Humectants.