Cosmetic ingredient reference

Hyaluronic acid: a formulator’s reference

Q: Hyaluronic acid or sodium hyaluronate?

Sodium hyaluronate is the sodium salt of hyaluronic acid and is what most cosmetic raw material actually is, because the salt is more stable and easier to handle as a dry powder. Both are separate INCI names — Hyaluronic Acid (CAS 9004-61-9) and Sodium Hyaluronate (CAS 9067-32-7) — and both, together with potassium hyaluronate, were covered by the same Cosmetic Ingredient Review safety assessment.

Q: What is the most important specification when buying hyaluronic acid?

Molecular weight, and it is not close. Hyaluronic acid is a polydisperse polymer, not a defined molecule: a given batch is a distribution of chain lengths, and everything a formulator cares about — viscosity, feel, solubility behaviour, how much can be loaded before the phase becomes unworkable, and whether the material penetrates at all — follows from that distribution. A supplier who cannot state the molecular weight range is not selling you a specified ingredient.

Q: What concentration is used?

The Cosmetic Ingredient Review reported hyaluronic acid, sodium hyaluronate and potassium hyaluronate functioning in cosmetics as skin conditioning agents at concentrations up to 2%. In practice the workable ceiling is set by molecular weight long before it is set by that figure — high-molecular-weight material builds viscosity so aggressively that fractions of a percent are often the practical limit, while low-molecular-weight grades can be used far higher without the same effect.

Q: Does hyaluronic acid actually penetrate skin?

Partly, and it depends on chain length. A 2025 review analysing the topical literature reported that hyaluronic acid below about 100 kDa penetrates skin, with lower molecular weights able to reach the dermis. The 2009 Cosmetic Ingredient Review also stated that hyaluronic acid does penetrate to the dermis. High-molecular-weight material largely does not, and is understood to act at the surface.

Q: Is low molecular weight better?

One double-blind randomised controlled trial in 36 elderly participants with dry skin compared low- and high-molecular-weight lotions against vehicle on separate sites, and reported higher skin capacitance for the low-molecular-weight site than for either the high-molecular-weight site or vehicle after four weeks. It also found no significant difference between any group in transepidermal water loss or symptom score. So: one measured hydration endpoint favoured the lower molecular weight, and two other endpoints did not separate. That is the honest answer, and it is a narrower one than the marketing.

Hyaluronic acid is the one ingredient in this cluster with a genuinely solid evidence base — an independent safety review, independently-run randomised trials, and a published account of what does and does not penetrate. It is also the one where the specification that matters is not on most certificates. It is not a molecule; it is a polymer, and its molecular weight distribution determines almost everything you will care about.

Reviewed by Jason Fleming — Biochemistry consultant, Nanyang Technological University, Singapore.Last reviewed: 2026-07-22

What hyaluronic acid is

Hyaluronic acid — also called hyaluronan — is a glycosaminoglycan: a long, unbranched polysaccharide built from a repeating disaccharide of D-glucuronic acid and N-acetyl-D-glucosamine. It is not a peptide, and it shares nothing chemically with the rest of this ingredient cluster; it sits here because formulators buy it from the same suppliers and search for it in the same breath.

It occurs naturally in human skin, where it is a structural component of the extracellular matrix with both structural and signalling roles. Commercial material is produced predominantly by bacterial fermentation; the 2009 Cosmetic Ingredient Review assessment notes bacterial fermentation and rooster combs as the two sources, and fermentation has become the dominant route since. Most raw material sold as “hyaluronic acid” is in fact the sodium salt, sodium hyaluronate, which handles better as a dry powder.

Why there is no single molecular weight

This is the point that catches people out. A batch of hyaluronic acid is a distribution of chain lengths, not a compound with one mass. Grades sold for cosmetic use span several orders of magnitude, from oligomeric fragments through to material well above a million daltons, and the chains behave completely differently at each end of that range. Viscosity, hydration behaviour, film-forming, skin feel, the maximum workable loading and whether the material penetrates at all are all consequences of the distribution. A certificate reporting “hyaluronic acid, 95% purity” with no molecular weight range on it has told you almost nothing useful.

Reference data

Property	Value
INCI names	Hyaluronic Acid; Sodium Hyaluronate; Potassium Hyaluronate
Class	Glycosaminoglycan — linear polysaccharide, not a peptide
Repeating unit	D-glucuronic acid + N-acetyl-D-glucosamine disaccharide
CAS — hyaluronic acid	9004-61-9
CAS — sodium hyaluronate	9067-32-7
Molecular weight	Not a fixed value — a polydisperse distribution. This is the specification to request.
Typical source	Bacterial fermentation (historically also rooster combs)
Physical form	White fibrous or granular powder; strongly hygroscopic
Solubility	Water-soluble; hydrates slowly and builds viscosity as it does
CIR reported use	Skin conditioning agent at concentrations up to 2%
Reported penetration threshold	Below ~100 kDa penetrates skin; lower MW reaches the dermis (Zanchetta 2025)

We do not give a single molecular formula or molecular weight for the polymer. The public chemical databases index short oligosaccharide fragments under the name, and quoting one of those as though it were the molecular weight of hyaluronic acid would be misleading rather than helpful.

What the evidence shows, and who ran it

The safety assessment

Becker et al. (2009) is the Cosmetic Ingredient Review Expert Panel’s final safety assessment of hyaluronic acid, potassium hyaluronate and sodium hyaluronate. It reported the ingredients functioning as skin conditioning agents at concentrations up to 2%, that hyaluronic acid does penetrate to the dermis, and that in the reviewed data it was not toxic across a range of acute animal studies, not immunogenic, not a sensitiser, not a reproductive or developmental toxicant and not genotoxic — concluding the ingredients safe for use in cosmetics as described. This is an independent expert-panel review, not a supplier document, and it is the reason this ingredient sits at the top of the evidence ranking in this cluster.

Penetration and molecular weight

Zanchetta, Scandolera and Reynaud (2025, Biomolecules) reviewed the topical literature specifically to ask which forms of hyaluronic acid penetrate skin and hair. Their analysis reported that material below approximately 100 kDa penetrates skin, with lower molecular weights able to reach the dermis. Note the disclosure: all three authors were employed by Givaudan, an ingredient supplier. That does not invalidate a literature review, but it is worth knowing, and it is stated in the paper.

The randomised topical trial

Muhammad et al. (2024, Arch Dermatol Res) ran a double-blind randomised controlled trial in 36 nursing-home residents aged 60–80 with dry skin, in Jakarta. Each participant received three lotions — low-molecular-weight hyaluronic acid, high-molecular-weight hyaluronic acid, and vehicle — applied to three separate randomised sites on the leg, with measurements at weeks 0, 2 and 4. After four weeks, skin capacitance was higher at the low-molecular-weight site than at the high-molecular-weight site (56.37 vs 52.37 AU, p = 0.004) and than at the vehicle site (56.37 vs 49.01 AU, p < 0.001). Transepidermal water loss and the symptom score showed no significant differences between any of the groups, and no side effects were seen. The trial was run by a university dermatology department and registered on ClinicalTrials.gov (NCT06178367).

That is a well-designed independent study, and it is worth reading exactly: one instrumental hydration endpoint separated in favour of the lower molecular weight, and two other endpoints did not separate at all. It supports a narrower claim than “low molecular weight works better,” and the narrower claim is the one that can be cited.

Delivery-system studies

Two further studies illustrate the barrier problem from the other direction. Jang et al. (2020, Int J Cosmet Sci) used high-molecular-weight hyaluronic acid in a dissolving microneedle, which physically bypasses the stratum corneum. Sundaram et al. (2018) evaluated a topical crosslinked hyaluronic acid serum in a prospective, randomised, investigator-blinded split-face study. Both are relevant to formulators considering whether the delivery format, rather than the ingredient, is doing the work.

Formulation and stability constraints

More is genuinely known here than for any other ingredient in this cluster, and the constraints are largely consequences of the polymer physics.

Hydration technique. The powder is hygroscopic and hydrates from the outside in, so dumping it into water produces gel-coated lumps that then take hours to disperse. Sprinkling onto a vortex, pre-dispersing in glycerin or another non-solvent, or hydrating overnight are the standard approaches. This is a handling property of hydrocolloids generally.
Viscosity scales sharply with molecular weight. High-molecular-weight grades build viscosity at fractions of a percent; low-molecular-weight grades can be used far higher without the same effect. The CIR’s 2% figure is a reported-use ceiling, not a target — for a high-molecular-weight grade it is generally unworkable well below that.
Chain scission is real. The polymer’s functional properties come from chain length, so anything that cuts chains changes the product: prolonged high shear, heat, strongly acidic conditions and free-radical-generating systems are the usual suspects. A formula that measures correctly on day one and thins over storage has usually lost molecular weight, not lost ingredient.
Polyanionic. The glucuronic acid units make the polymer anionic at cosmetic pH, so it interacts with cationic ingredients — quaternary conditioning agents, cationic preservatives, and cationic peptides such as Acetyl Tetrapeptide-3 — potentially forming complexes or precipitates. This follows from the charge and is a standard compatibility check.
It is a nutrient source. A sugar polymer in water is a substrate for microbial growth; hyaluronic acid solutions need a properly validated preservative system, and preservative-efficacy testing is not optional.

As dry powder, store sealed and dry — it will pull moisture out of the air and cake if left open. See how to store peptides for the general cold-chain and moisture logic, which applies here for the same reason.

Verifying identity and quality

The analytical questions for a polysaccharide are different from those for a peptide, and this is where a certificate written for peptides falls short. HPLC purity and a mass-spectrometry identity check — the two lines that carry a peptide certificate — do not translate cleanly to a polydisperse polymer.

What actually characterises a hyaluronic acid batch:

Molecular weight distribution, typically by size-exclusion chromatography. This is the specification, and it should be a range, not a single number.
Assay / glucuronic acid content — how much of the powder is actually the polymer rather than salt and moisture.
Residual protein and endotoxin — a consequence of the fermentation route, and the reason the pharmaceutical and cosmetic grades of the same polymer command different prices.
Microbiological limits and heavy metals, as for any fermentation-derived raw material.

A supplier who supplies only “purity 95%” with no molecular weight range has answered the wrong question. See how to read a COA; batches we ship are on verify.

Verify a batch

Every order ships with a per-batch Certificate of Analysis. Have a vial in hand? Enter its lot number to look up the COA for that exact batch.

Verify a batch →How to read a COA

What is not established

That topical hyaluronic acid replenishes the skin’s own hyaluronic acid content. Penetration to the dermis is reported; that is a different statement from replacement, and we have not seen the latter demonstrated.
That low molecular weight is broadly superior. One randomised trial separated on a hydration measure and did not separate on transepidermal water loss or symptom score.
A defined optimal molecular weight for any given application. The published penetration threshold (~100 kDa) is a boundary, not an optimum.

Sourcing

Supplied as raw material with a per-batch Certificate of Analysis. Not supplied as a finished cosmetic, and a certificate is not a cosmetic safety assessment. Note that vial-scale quantities suit laboratory and small-batch formulation work; production formulation normally buys this polymer by weight at a specified molecular weight grade, and the grade should be agreed at enquiry rather than assumed.

The rest of the cluster, with live availability, is on the cosmetic ingredient hub; the separate research-compound catalogue is at /catalog.

Frequently asked questions

Hyaluronic acid or sodium hyaluronate?

Sodium hyaluronate is the sodium salt of hyaluronic acid and is what most cosmetic raw material actually is, because the salt is more stable and easier to handle as a dry powder. Both are separate INCI names — Hyaluronic Acid (CAS 9004-61-9) and Sodium Hyaluronate (CAS 9067-32-7) — and both, together with potassium hyaluronate, were covered by the same Cosmetic Ingredient Review safety assessment.

What is the most important specification when buying hyaluronic acid?

Molecular weight, and it is not close. Hyaluronic acid is a polydisperse polymer, not a defined molecule: a given batch is a distribution of chain lengths, and everything a formulator cares about — viscosity, feel, solubility behaviour, how much can be loaded before the phase becomes unworkable, and whether the material penetrates at all — follows from that distribution. A supplier who cannot state the molecular weight range is not selling you a specified ingredient.

What concentration is used?

The Cosmetic Ingredient Review reported hyaluronic acid, sodium hyaluronate and potassium hyaluronate functioning in cosmetics as skin conditioning agents at concentrations up to 2%. In practice the workable ceiling is set by molecular weight long before it is set by that figure — high-molecular-weight material builds viscosity so aggressively that fractions of a percent are often the practical limit, while low-molecular-weight grades can be used far higher without the same effect.

Does hyaluronic acid actually penetrate skin?

Partly, and it depends on chain length. A 2025 review analysing the topical literature reported that hyaluronic acid below about 100 kDa penetrates skin, with lower molecular weights able to reach the dermis. The 2009 Cosmetic Ingredient Review also stated that hyaluronic acid does penetrate to the dermis. High-molecular-weight material largely does not, and is understood to act at the surface.

Is low molecular weight better?

One double-blind randomised controlled trial in 36 elderly participants with dry skin compared low- and high-molecular-weight lotions against vehicle on separate sites, and reported higher skin capacitance for the low-molecular-weight site than for either the high-molecular-weight site or vehicle after four weeks. It also found no significant difference between any group in transepidermal water loss or symptom score. So: one measured hydration endpoint favoured the lower molecular weight, and two other endpoints did not separate. That is the honest answer, and it is a narrower one than the marketing.

Literature cited

Becker LC, Bergfeld WF, Belsito DV, et al.; Cosmetic Ingredient Review Expert Panel. “Final report of the safety assessment of hyaluronic acid, potassium hyaluronate, and sodium hyaluronate.” Int J Toxicol. 2009;28(4 Suppl):5–67. PMID 19636067. pubmed.ncbi.nlm.nih.gov/19636067. (Source of the 2% figure and the dermal-penetration statement.)
Zanchetta C, Scandolera A, Reynaud R. “Hyaluronic Acid in Topical Applications: The Various Forms and Biological Effects of a Hero Molecule in the Cosmetics Industry.” Biomolecules. 2025;15(12):1656. PMID 41463312. pubmed.ncbi.nlm.nih.gov/41463312. (Source of the <100 kDa penetration threshold; all three authors employed by Givaudan.)
Muhammad P, Novianto E, Setyorini M, et al. “Effectiveness of topical hyaluronic acid of different molecular weights in xerosis cutis treatment in elderly: a double-blind, randomized controlled trial.” Arch Dermatol Res. 2024;316(6):329. PMID 38829483. pubmed.ncbi.nlm.nih.gov/38829483. (n = 36; ClinicalTrials.gov NCT06178367.)
Jang M, Baek S, Kang G, et al. “Dissolving microneedle with high molecular weight hyaluronic acid to improve skin wrinkles, dermal density and elasticity.” Int J Cosmet Sci. 2020;42(3):302–309. PMID 32421218. pubmed.ncbi.nlm.nih.gov/32421218.
Sundaram H, Cegielska A, Wojciechowska A, Delobel P. “Prospective, Randomized, Investigator-Blinded, Split-Face Evaluation of a Topical Crosslinked Hyaluronic Acid Serum for Post-Procedural Improvement of Skin Quality and Biomechanical Attributes.” J Drugs Dermatol. 2018;17(4):442–450. PMID 29601621. pubmed.ncbi.nlm.nih.gov/29601621.

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