How Far Into Skin Does Hyaluronic Acid Get? Molecular Weight Sets the Limit
Research Team
Depth falls as molecular weight rises. In Raman measurements of human skin using 1 % aqueous solutions, hyaluronic acid of 20–50 kDa was detected to about 100 µm, 100–300 kDa to about 50 µm, and 1,000–1,400 kDa only within the stratum corneum, to about 25 µm — as reported in the 2025 review by Zanchetta and colleagues.
Published 26 October 2026 · Last reviewed 29 October 2026
Why the question has a numerical answer
Hyaluronic acid is not one ingredient. It is a single repeating polymer supplied across more than four orders of magnitude of chain length, and the chain length changes the physics of what happens after application. A molecule of 800 Da and a molecule of 2,000 kDa share an INCI name and almost nothing else that matters to percutaneous transport.
That makes "does hyaluronic acid penetrate?" an unanswerable question as posed, and "how far does which hyaluronic acid get, measured how?" an answerable one.
Definitions used in this article
- Hyaluronic acid (hyaluronan). A linear glycosaminoglycan of repeating D-glucuronic acid and N-acetyl-D-glucosamine units, strongly hydrophilic, present natively in the dermal extracellular matrix.
- Molecular weight classes. In the review cited here: low-molecular-weight hyaluronic acid below 50 kDa; medium-molecular-weight 100–500 kDa; high-molecular-weight above 700 kDa. Native hyaluronan in tissue can reach 6,000 kDa.
- Stratum corneum. The outermost non-living epidermal layer, roughly 10–20 µm thick on most body sites, and the principal barrier to percutaneous absorption.
- Confocal Raman spectroscopy. An optical method that records a molecular vibrational spectrum at successive depths, producing a depth profile without sectioning the tissue.
- Tape stripping. Sequential removal of stratum corneum layers with adhesive tape, allowing the quantity of a substance per unit area to be measured layer by layer.
The depth data
The figures below are collated in a 2025 open-access review in Biomolecules. They are the review's report of primary studies; where this article states a depth, the depth is as the review states it. The primary Raman paper itself was not accessible for direct reading, and that limitation is recorded here rather than concealed.
| Molecular weight | Method / model | Reported depth or outcome |
|---|---|---|
| 2 kDa | Excised skin | Reaches the dermis |
| 3 kDa | Skin explants, 8 h | Up to 60 µm |
| 10 kDa | Labelled, 24 h | Distributed in stratum corneum; weak signal in viable epidermis |
| 20–50 kDa | Raman, 1 % in water | Up to 100 µm (deepest epidermis) |
| 100–300 kDa | Raman, 1 % in water | Up to 50 µm (superficial epidermis) |
| 200–325 kDa | Franz cell, full-thickness abdominal skin | Reaches dermis, but only 2–3 % of the applied dose enters skin at all |
| 400 kDa | Radiolabelled, in vivo forearm | Absorbed as far as the dermis |
| 1,000 kDa | Excised skin | Did not pass the stratum corneum |
| 1,000–1,400 kDa | Raman, 1 % in water | Stratum corneum only, up to 25 µm |
A separate kinetic study cited in the same review compared twelve hyaluronic acid grades from 0.4 to 2,000 kDa on porcine skin. Molecular weight accounted for approximately 60 % of the variability in penetration. Between 27 % and 39 % of the deposited material reached the epidermis for every grade except a cross-linked polymer; more than 50 % reached the dermis for grades between 0.4 and 100 kDa, with the highest figure, 75 %, at 0.8 kDa; around 25 % of the 200 kDa and 500 kDa grades reached the dermis.
The quantity problem, which is separate from the depth problem
Depth and dose are routinely conflated in commercial copy, and the numbers above show why they should not be. For the 200–325 kDa grade measured in a Franz cell, the review reports that the material reaches the dermis — and that only 2–3 % of the applied dose enters the skin in the first place. "Reaches the dermis" is therefore a statement about the tail of a distribution, not about the bulk of what was applied.
The remainder is not inert. A clinical tape-stripping study cited in the review, using an emulsion containing both a 100–1,400 kDa fraction and a 20–50 kDa fraction, found accumulation in the stratum corneum rising from under 10 ng/cm² on day 0 to over 1,000 ng/cm² by day 7 of repeated application. High-molecular-weight hyaluronan that does not cross the barrier is building a hydrated film on and within the stratum corneum, which is a different mechanism from dermal delivery and should be described as such.
Chemical modification shifts the limit independently of chain length: the review reports an acetylated 15 kDa hyaluronic acid detected to about 100 µm in skin explants against about 50 µm for the unmodified polymer of the same weight. Molecular weight is the dominant variable, not the only one.
Where the evidence is weaker than the summary suggests
Four caveats belong with the table, and omitting them would misrepresent the literature.
First, the review is internally inconsistent on the threshold. Its abstract states that hyaluronic acid below 100 kDa penetrates skin, while a later section sets the figure at 400 kDa for diffusion within the stratum corneum, and several of the studies it tabulates report dermal penetration at 200–400 kDa. No single threshold is defensible from this body of work.
Second, the models are not equivalent. Porcine skin, excised human skin, skin explants and in vivo forearm measurements have different barrier integrity and different clearance, and depths obtained in one are not transferable to another.
Third, detection is not function. A Raman or fluorescence signal at 100 µm establishes that material is present at that depth. It establishes nothing about concentration relative to an effective threshold, about residence time, or about what the molecule does once there.
Fourth, several of the quoted values are ranges reported without dispersion statistics, so the apparent precision of "up to 100 µm" should not be read as a measured mean with a known error.
What this means for formulation
The useful conclusion is that chain length is a formulation specification, not a marketing adjective, and that a formulation combining grades is making two different physical bets at once: a surface-hydration bet on the high-molecular-weight fraction and a transport bet on the low-molecular-weight fraction. Stating which grades are present, at what weight ranges, is the part of the claim that is verifiable. "Penetrates deeply", with no weight stated, is the part that is not.
The same constraint governs smaller actives. Molecular size and lipophilicity together set what can cross the stratum corneum, which is why ascorbic acid and its lipophilic ester behave so differently from one another; that case is treated in our own open-access technical report.
Scope note
This article describes findings published in the peer-reviewed literature on the percutaneous penetration of hyaluronic acid. It is written for researchers and healthcare professionals, is not medical advice, and does not constitute a claim about any product. Cosmetic products are not intended to diagnose, treat, cure or prevent disease.
References
- TTS Clinical Scientific Team (2026). Topical Vitamin C: the pH Constraint on L-Ascorbic Acid and the Oxidative Stability of Tetrahexyldecyl Ascorbate, version 1.0. Zenodo. CC BY 4.0. DOI 10.5281/zenodo.22491021 (concept DOI, all versions: 10.5281/zenodo.22491019).
- 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. DOI 10.3390/biom15121656.