Hyaluronic acid (Sodium hyaluronate)

The short answer

Sodium hyaluronate is the salt form of hyaluronic acid that almost all skincare uses. Slightly more stable, slightly smaller molecule, same job. It's a humectant: it holds water in the upper layers of your skin like a sponge holds water at the kitchen sink. The skin feels plumper, softer, less tight, especially through the day in a dry office or a centrally-heated flat in February.

It is not a treatment. It does not rebuild your skin. It is, however, one of the safest, best-tolerated ingredients in cosmetic chemistry. Almost everyone can use it, and it pairs with almost everything else.

If you've been sold an HA serum as the cornerstone of an anti-aging routine and quietly wondered why nothing changed: that's the marketing, not your skin. HA is the housekeeper, not the architect.

What the evidence actually shows

Surface hydration. Multiple controlled studies (Pavicic 2011, Bukhari 2018) confirm that topical HA increases stratum corneum hydration measurably within hours and sustains it with continued use. That's the headline finding. Reliable, repeatable, unspectacular in the best way.

Modest wrinkle effects. Pavicic's work suggested that lower-molecular-weight HA penetrated slightly deeper and showed small but measurable reductions in wrinkle depth over 60 days. The effect size is modest and the photographs in the paper aren't dramatic. Don't expect transformation.

Endogenous HA and aging. Papakonstantinou's review documents that hyaluronic acid is a real and important component of the dermal extracellular matrix, and that its synthesis declines with age and UV exposure. But topical application doesn't meaningfully reach the dermis. The marketing that implies your serum "replenishes the HA you've lost with age" is overselling the mechanism. The molecule on your serum and the molecule deep in your dermis live in different postcodes.

How to use it

The one technique that actually matters: apply on damp skin.

A humectant doesn't make water. It moves it. On parched skin in a dry room, HA can pull moisture upward from the deeper skin layers and out into the air, leaving you tighter than before. The fix takes two seconds: a fine mist of water (or a splash) before HA, then a real moisturiser sealed on top.

• Morning and evening is fine.
• Pairs with everything: niacinamide, retinol, vitamin C, salicylic acid. The cushion between actives and the rest of your routine.
• Especially useful in winter and on planes when ambient humidity drops below 30 percent.

What it won't do

• Rebuild collagen. That's retinol's lane.
• Fix dehydration if you're not also sealing it in with an occlusive layer. Otherwise the sponge just dries.
• Replace a moisturiser for genuinely dry skin types. HA is a layer, not the whole routine.
• Help cystic acne, severe pigmentation, or photoaged skin in any meaningful way.

If a brand is marketing HA as a transformative anti-aging treatment, that's a marketing tell, not a clinical one. Treat it the way you'd treat a "miracle" headline in a tabloid.