Hyaluronic acid

Hyaluronic acid is something the human body makes for itself; skincare uses its more stable sodium salt, sodium hyaluronate. It is produced by fermentation rather than from animal sources, and its role is simple: to bind water and hold it where it is needed. Skin that holds water feels softer and looks smoother — and fine lines show less on it.

Treating hyaluronic acid as one ingredient is misleading, though. Molecular size decides a great deal. Large molecules stay at the surface and form a film that slows evaporation; smaller ones reach a little deeper into the upper layers. Even the smallest go nowhere deep — skincare works in the upper layers and nothing else can honestly be claimed for it. The difference is whether skin receives moisture only on top, or a storey down as well.

The second thing people rarely hear is the condition attached. Hyaluronic acid binds water but does not hold it by itself. In very dry air it can draw water from the skin, and applied to dry skin and left uncovered it can end up leaving skin drier. So it belongs on damp skin, and a layer that seals it must follow.

In the No3. Hydro Boost Collagel Serum it therefore sits in a matrix of different molecular sizes, alongside Sodium PCA and Acetyl Hexapeptide-8. In the ritual it comes third — after toning, which dampens the skin, and before the finishing serum, which seals the moisture in. That order is not arbitrary; reversed, the hydration never reaches the skin at all.

On a label, hyaluronic acid hides under several names: sodium hyaluronate, hyaluronic acid, sodium acetylated hyaluronate or hydrolysed hyaluronic acid. Different names usually mean different molecular sizes rather than different quality. What a label cannot tell you is the concentration — and that is fine, because with this ingredient more is not better. Above roughly one per cent the gain no longer justifies the tackiness it brings, and a good formula shows itself in the company it keeps.