Hyaluronic acid (HA) has traditionally been associated with skin care products; however, interest in it within the hair care segment is also steadily growing. Market dynamics confirm this: whereas in 2005 the use of sodium hyaluronate in non-coloring hair products on the U.S. market was registered in 12 formulations, by 2023 this number had risen to 83 [1]. Thus, this is not a matter of isolated inclusion of HA in formulations, but of a marked expansion of its presence in the hair product category.

At the same time, regarding hair, HA cannot be considered a universal ingredient. Its properties depend on the form in which it is incorporated, its molecular weight, and the carrier formulation. Of particular interest are low-molecular-weight forms of HA, especially those with a molecular weight below 50 kDa, since these were the forms that demonstrated the ability to penetrate more deeply into the hair fiber and interact with keratin [1]. This distinguishes the hair care segment from skin care, where high-molecular-weight forms are often valued for film formation and surface hydration.

In which product categories is HA used and in what form is it incorporated?

HA is already used in several types of hair care products and systems. These include shampoos, primarily smoothing formulations and products designed to reduce frizz. In a 2019 study, the active ingredient was incorporated into a shampoo as hydrolyzed sodium hyaluronate; at the same time, both tested active systems had the same international cosmetic ingredient name but differed in the ratio of fractions of different molecular weights [3]. This means that, despite identical ingredient labeling, the actual composition of the active complex could differ substantially.

This group also includes rinse-off formulations, for which retention of HA on the hair after rinsing is particularly important. In 1994, it was shown that a complex of hyaluronic acid with the cationic cellulose polymer polyquaternium-10 increased its affinity for keratin [2]. In this case, HA acted not simply as a free moisturizing component but as part of an associative complex capable of enhancing deposition onto the keratin substrate and preserving its effect after contact with water.

Conditioning compositions constitute a separate category. A combination of HA, collagen, and chitosan in conditioning systems is also mentioned [1]. This shows that HA is regarded not only as an independent active ingredient but also as a component of multicomponent formulations aimed at improving hair condition.

HA is also used in restorative leave-in products for damaged hair. In a 2022 study, sodium hyaluronate with different average molecular weights—1460, 370, and 42 kDa—was compared in a model of repeated application to overbleached hair; the most pronounced improvement in mechanical properties was obtained for the low-molecular-weight fraction of about 42 kDa [4]. Consequently, not only the presence of HA in the formulation matters, but also its molecular weight, which is an independent determinant of efficacy.

The literature also describes combined systems consisting of high- and low-molecular-weight HA. In a 2024 study, high-molecular-weight hyaluronic acid with a molecular weight of 1000–1400 kDa and low-molecular-weight hyaluronic acid with a molecular weight of 20–50 kDa were incorporated into a shampoo separately and as a mixture; it was the mixture that demonstrated the most interesting result in terms of penetration into the cortex and functional effects [1].

In addition to conventional topical care for hair length, the literature reports a non-crosslinked hyaluronic acid solution containing amino acids that were studied in dermal papilla cells [1, 5]. This direction lies at the intersection of trichology and local intradermal approaches; therefore, such products should be classified as conventional hair care products with caution.

What do the referenced studies show?

The earliest of the cited works is the 1994 study by Pavlichko et al. The PubMed abstract states that the combination of biotechnologically produced hyaluronic acid with polyquaternium-10 formed a stable multifunctional associative complex. As a result, HA became more substantive to keratin: according to radiolabeling methods, the amount of HA bound to hair after rinsing with water could increase up to tenfold [2]. This was associated with longer HA contact with keratin surfaces and, accordingly, with a more prolonged moisture-retaining, moisturizing, and smoothing effect. From a practical perspective, this is one of the key studies explaining why, for rinse-off formulations, not only HA itself but also its delivery and retention system on the hair is important.

The next important body of evidence concerns smoothing activity and frizz reduction. In 2019, the efficacy of a smoothing shampoo was evaluated using confocal Raman spectroscopy [3]. The PubMed abstract states that the effective active ingredient reduced the proportion of alpha-helical keratin conformation and promoted the formation of beta-structures, while also decreasing the intensity of bands corresponding to covalent cystine disulfide cross-links. It is specified that active A was effective, whereas active B was not; at the same time, both were designated as hydrolyzed sodium hyaluronate according to the international cosmetic ingredient nomenclature, but differed in the composition of fractions with different molecular weights [3]. For the topic of HA in hair care, this is fundamental: even with the same ingredient name, the result may depend on the molecular-weight distribution within the hydrolyzed fraction.

The 2022 study by Qu et al. supplements these data with findings on damaged hair [4]. The PubMed abstract states that low-molecular-weight hyaluronate, with an average molecular weight of approximately 42 kDa, significantly improved the mechanical properties, particularly the elastic modulus, of overbleached hair. Fluorescent labeling showed that it was specifically the low-molecular-weight form that penetrated the hair cortex, whereas the high-molecular-weight form was mainly retained on the outside. Additional methods—Fourier-transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry—made it possible to suggest the formation of additional intermolecular hydrogen bonds in the treated hair and stronger water binding within the fiber [4]. Therefore, the effect concerned not only “moisturization” in the everyday sense, but also a possible influence on the internal hydrogen-bonded network of keratin.

The 2024 study by Boira et al. is also noteworthy [1]. High-molecular-weight hyaluronic acid (1000–1400 kDa) and low-molecular-weight hyaluronic acid (20–50 kDa) were incorporated separately into a shampoo and as a mixture for the treatment of natural, non-dyed tresses. Both forms were detected in the cuticle, but only the mixture of the two molecular-weight ranges penetrated significantly into the cortex; it was this combination that exhibited straightening properties, increased the water content of the hair, and improved the elasticity and strength of bleached hair [1]. A search for the exact title of the article in PubMed did not yield any results; therefore, a more detailed characterization is limited to the information provided in the review publication [1].

Finally, the 2021 study by Zerbinati et al. concerns not the hair shaft, but dermal papilla cells [5]. According to the PubMed abstract, a non-crosslinked hyaluronic acid with several amino acids was studied in human hair follicle dermal papilla cells. Restoration of cell viability after ultraviolet-induced cytotoxicity and an increase in vascular endothelial growth factor secretion were demonstrated, interpreted as evidence of the product’s ability to modulate dermal papilla cells [5]. At the same time, this does not concern a proven clinical effect of routine cosmetic hair care on hair growth, but rather a promising direction for further research, including in the context of mesotherapy. This distinction is important: there is a substantial gap between in vitro results and actual cosmetic effects on hair.

Practical conclusions

Several fairly clear practical conclusions follow from the available data.

1. In hair care, not merely the presence of HA in the formulation matters, but its form. For shampoos and other rinse-off formulations, the ability to be retained on keratin after contact with water is important. This is why HA complexes with cationic polymers, rather than only “free” HA, are of particular interest [2].
2. For effects on the hair fiber itself, molecular weight is especially important. The most convincing data for damaged hair have been obtained for low-molecular-weight HA, primarily around 42 kDa, as well as for mixtures of low- and high-molecular-weight fractions [1, 4]. These are the systems that, in studies, penetrated more deeply and were associated with improved hair elasticity, strength, and water status.
3. In shampoos, HA may act not only as a moisturizer but also as a smoothing active ingredient when hydrolyzed fractions with a specific molecular weight profile are used. Confocal Raman spectroscopy data show that frizz reduction may be associated with changes in keratin conformation rather than only with a superficial cosmetic feel [3].
4. High-molecular-weight HA does not appear to be the most promising form for the independent restoration of damaged hair if penetration into the cortex is the primary goal. Based on the available data, its role is more likely superficial or enhancing when used in combined systems [1, 4].
5. The “HA and hair growth” direction cannot yet be placed on the same level as the data on hair length and the hair fiber itself. For this topic, predominantly cellular data, rather than convincing clinical results from conventional cosmetic hair products, are available [1, 5].

Overall, HA in hair care has already moved beyond being an exotic ingredient, but its use cannot be viewed in an oversimplified way. For hair length, the most interesting forms today are hydrolyzed and low-molecular-weight forms, as well as compositions that increase HA retention on keratin or combine different molecular-weight ranges. It is within this framework that new products on the market should be evaluated: not by the presence of the word hyaluronic on the packaging, but by which specific form of HA has been incorporated into the formulation and what function it performs there.

References

1. 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: 1656.
2. Pavlichko J.P., Goddard E.D., Band P.A., Leschiner A. Enhanced substantivity of hyaluronic acid on keratin substrates via polymer complexation. Int J Cosmet Sci 1994; 16(6): 227–234.
3. Essendoubi M., Meunier M., Scandolera A. et al. Confirmation changes in human hair keratin observed using confocal Raman spectroscopy after active ingredient application. Int J Cosmet Sci  2019; 41(3): 203–212.
4. Qu W., Guo X., Xu G., et al. Improving the mechanical properties of damaged hair using low-molecular weight hyaluronate. Molecules 2022; 27(22) 7701.
5. Zerbinati N., Sommatis S., Maccario C. et al. In vitro hair growth promoting effect of a noncrosslinked hyaluronic acid in human dermal papilla cells. Biomed Res Int 2021; 2021: 5598110.
6. Boira C., Essendoubi M., Meunier M. et al. Hyaluronic acid: elucidating its penetration into, and effect on hair fibers using confocal Raman spectroscopy and biometric techniques. J Phys Chem Biophys 2024; 14: 000373.