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Hyaluronic acid

Hyaluronic acid in skincare: Humectant. What it does on skin, how strong the evidence behind the claim actually is, the concentrations in normal use, who reacts to it, and where it stands in pregnancy and sunlight. On a label it appears as Sodium Hyaluronate, Hyaluronic Acid, Hydrolyzed Hyaluronic Acid.

Hydration, emollients and barrier repairHumectantEvidence: Moderate

On the label: Sodium Hyaluronate, Hyaluronic Acid, Hydrolyzed Hyaluronic Acid. Also called: HA, hyaluronan.

This is an ingredient reference, not a diagnosis and not a treatment plan. It describes what substances are and what the published evidence supports; it does not tell you what your skin has or what to put on it. A rash that spreads, hurts, weeps, does not settle, or comes with feeling unwell is a reason to see a doctor or pharmacist, not to change serum.

What it is

A long sugar chain that the body makes in large quantities, most of it in the dermis and in joint fluid, where it holds water and gives tissue its springiness. The cosmetic ingredient is produced by bacterial fermentation rather than extracted from animals, and it is usually supplied as the sodium salt, sodium hyaluronate, which is why that is the name you see on the label rather than the one on the front of the box.

What it does on skin

On skin it works as a humectant: it binds water and holds it at the surface in a hydrated film, which makes the outer layer more flexible and makes fine lines look temporarily softer. High-molecular-weight forms stay on top and reduce water loss a little; the hydrolysed, low-molecular-weight fragments penetrate the upper dead layer. Neither reaches the dermis, and neither replaces what is there.

What the evidence is worth

Evidence: Moderate

Good short-term evidence for surface hydration and for the appearance of fine lines while the skin is hydrated. No evidence that a topical product restores the hyaluronic acid content of the dermis, which is what injectable fillers do in a clinic under an entirely different regulatory regime. The molecular-weight arguments printed on packaging run well ahead of published comparisons.

How it is used

On damp skin, followed by a moisturiser. That order is the whole trick: a humectant needs water to hold, and something over the top to stop it evaporating. Applied to dry skin in cold dry air and left uncovered, a hyaluronic serum can leave skin feeling tighter than before you started.

Typical concentration in normal use: 0.1-2% (it is used at low percentages). That is a description of the market, not a recommendation, and it is not a dose.

Who reacts to it

One of the least irritating ingredients in cosmetics; reactions are rare and usually trace to another ingredient in the same serum. The most common complaint is a tacky film or pilling under makeup, which is a formulation quality issue rather than a safety one.

Pregnancy and breastfeeding

Generally considered fine

Topical hyaluronic acid raises no pregnancy concerns and is a sensible core ingredient during the months when retinoids and stronger actives are on hold.

Sunlight

No change

No effect on light sensitivity in either direction.

Rules and labelling

Not restricted in cosmetics. Worth knowing that "hyaluronic acid" in a syringe is a medical device or medicine handled by a trained practitioner, and the shared name on a serum bottle is the same molecule doing a completely different job.

What it goes with, and what it does not

It pairs with everything and is most useful directly under an occlusive moisturiser. It is also the standard rescue layer when an acid or a retinoid has left skin tight.

One thing people get wrong

The myth is the number: hyaluronic acid holding a thousand times its weight in water. That is a laboratory property of the pure polymer, not a claim about a serum, and holding water in a beaker is not the same as putting it into skin. The related myth is that a serum "plumps from within" — it plumps the outer layer with water, and that goes when the water goes.

Sources: EU Cosmetics Regulation (EC) No 1223/2009 and its annexes, as published in the European Commission's CosIng database, for every statement about what is permitted, restricted or banned · opinions of the Scientific Committee on Consumer Safety (SCCS) and safety assessments of the Cosmetic Ingredient Review (CIR) for the concentration positions · standard dermatology reference material for mechanism, tolerability and contact-allergy patterns · checked 2026-09-06. Deep links are deliberately omitted where a stable public URL could not be confirmed.

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