Hyaluronic Acid

Hyaluronic acid (HA) is a polysaccharide that already exists naturally in human skin, where it helps regulate water balance in the extracellular matrix. Applied topically, it works as a humectant: it attracts and binds water from the surrounding environment, holding it at the skin's surface to visibly plump and hydrate.

You will see it on ingredient lists in two forms. Sodium hyaluronate is the salt of hyaluronic acid and the standard form used in skincare, valued for being stable and easy to formulate. Hydrolysed hyaluronic acid is hyaluronic acid broken into much smaller fragments. Formulas that combine both are described as multi-weight (multi-molecular-weight) hyaluronic acid: larger molecules tend to stay on the skin's surface and help hold water there, while smaller fragments give a lighter feel and are used to hydrate the outer layers of skin. All forms work the same way, as humectants, so the difference is mainly in how a formula feels and how the hydration is delivered.

Because it is a humectant rather than an occlusive, hyaluronic acid works best layered under a moisturiser that helps seal that water in. In very dry air, a humectant applied alone can pull moisture from deeper skin layers instead of the atmosphere, which is why it's formulated alongside richer ingredients like shea butter or ceramides rather than used alone.

In practice, hyaluronic acid works well morning and night, applied to damp skin so it has moisture to draw from, then sealed with a moisturiser. It layers well with almost every other active in a routine and has no meaningful caution attached to it, making it one of the gentler ingredients to introduce for the first time.