What it is
Hyaluronic acid, also called hyaluronan, is a glycosaminoglycan: a long chain of repeating pairs of two sugars, D-glucuronic acid and N-acetyl-D-glucosamine.1 It is present in all the body's tissues and fluids, and most abundant in the skin, which holds about half of the body's total. A review of its role in skin ageing calls it the key molecule involved in skin moisture, because of its capacity to bind and retain water.1
For cosmetics, according to the US Cosmetic Ingredient Review (CIR), it is obtained mainly from bacterial fermentation and from rooster combs.2 The label name is the same whichever source was used.
What it does in a formula
The EU's CosIng database lists four functions for hyaluronic acid3, each with a set definition4:
- Humectant: retaining or preserving the moisture in a product during use.
- Moisturising: increasing the water content of the skin and keeping it soft and smooth.
- Skin conditioning: maintaining the skin in good condition.
- Antistatic: preventing or reducing static electricity by neutralising electrical charge on surfaces.
It also changes texture. Hyaluronic acid takes up a large volume of water, which gives its solutions a high viscosity even at low concentrations1, so a small amount thickens a water-based formula. How it compares with glycerin, the other humectant found on most moisturiser labels, is set out in glycerin vs hyaluronic acid.
The acid and its salts
Hyaluronic Acid is one of several related label names. Its sodium salt, Sodium Hyaluronate, has its own CosIng entry, with humectant and skin conditioning as its functions5, and the CIR assessed the acid together with its sodium and potassium salts.2 A front label that says "hyaluronic acid" may mean any of them.
None of these names carries a molecule size. "Low molecular weight" or "multi-weight" on a pack is the brand's description; the sodium hyaluronate page explains what one laboratory study found about size and skin.
What official sources say
Hyaluronic acid has no entry in the annexes of the EU cosmetics regulation, which list the substances that are banned, restricted, or allowed as colourants, preservatives or UV filters6, so EU law sets no specific limit or warning for it.
The CIR recorded hyaluronic acid and its salts in use as skin conditioning agents at concentrations up to 2%. Its panel found the acid was not a sensitiser in animal studies, noted that its widespread clinical use, mainly by injection, had been free of significant adverse reactions, and concluded that hyaluronic acid and its sodium and potassium salts are safe for use in cosmetics as described in its assessment.2 That conclusion is about the ingredients as reviewed, not about any one product.
How it appears on a label
- Hyaluronic Acid is the name in the EU glossary of label names7; CosIng records it under CAS number 9004-61-9.3
- Sodium Hyaluronate, Hydrolyzed Hyaluronic Acid and other relatives are separate ingredients, each counted on its own.
- Position: in the EU, ingredients below 1% may be listed in any order after the rest8, so where it sits is a weak clue to how much there is. Ingredient list order explains the rule.
- Check a whole list with the skincare ingredient checker to see the other humectants, emollients and occlusives around it.