What are the benefits of hyaluronic acid for the scalp and hair?

The hyaluronic acid is a naturally occurring molecule in the body, renowned for its remarkable ability to attract and retain water. Depending on its molecular weight, it can even bind up to 1,000 times its weight in water. This property, highly beneficial for the skin, could also be relevant for hair. Indeed, each hair fiber is composed of three superimposed layers – the medulla, the innermost layer; the cortex, which makes up nearly 80% of the hair; and the cuticle, the external protective layer. The cuticle consists of flat cells that overlap like shingles, and their cohesion is essential for limiting water loss.

To date, few studies have examined the hair-related properties of hyaluronic acid. One study evaluated the effects of hyaluronic acids of different molecular weights on the mechanical properties of hair fibers. For this purpose, hyaluronic acids of 1,460 kDa (high molecular weight), 370 kDa (medium molecular weight), and 42 kDa (low molecular weight) were used. Hair tresses were treated with a spray containing 0.25% of one of these hyaluronic acids, then subjected to tensile tests to measure their strength. The results showed that only the low molecular weight hyaluronic acid significantly increased the tensile strength of hair fibers (+16%), without altering their elongation at break.

This study also evaluated the penetration capacity into hair fibers of these different molecular weights of hyaluronic acid. Using fluorescence microscopy, it was observed that low-molecular-weight hyaluronic acid exhibited a significantly higher fluorescence intensity than the high-molecular-weight form, indicating deeper penetration. Cross-sectional images showed that low-molecular-weight hyaluronic acid reached all regions of the fiber, including the cortex, whereas the high-molecular-weight variant remained largely in the outer layers. This distribution difference suggests that the ability of low-molecular-weight hyaluronic acid to restore the mechanical properties of the hair fiber is directly linked to its deeper penetration into the hair’s internal structure.

Another study reached the same conclusions. Researchers evaluated the effect of four different biopolymer-enriched conditioners (collagen, hyaluronic acid, a 50/50 collagen–hyaluronic acid blend, and a 50/50 collagen–hyaluronic acid blend with 30% chitosan) compared to a conditioner without biopolymers on the mechanical properties of human hair. Strands of brown hair from a 20-year-old woman were washed, dried, treated with one of the conditioners for 30 minutes, then rinsed and allowed to air dry. The hair was then subjected to mechanical tests (Young’s modulus and elongation at break) using a tensile testing machine. The results, shown in the graph below, indicate that the presence of hyaluronic acid in the conditioners significantly increases Young’s modulus, reflecting an improvement in the strength of the hair fibers.

In addition, other studies have investigated combining hyaluronic acid with a cationic polymer, polyquaternium-10, to improve its affinity for keratinous surfaces such as hair fibers. This complex, named BHA-10, exploits the electrostatic interaction between negatively charged hyaluronic acid and positively charged polyquaternium-10 to overcome the natural repulsion between hyaluronic acid and the hair fiber. Zeta potential measurements and radiolabeling tests have shown that this complexation increases hyaluronic acid adsorption on hair by a factor of 10 after a simple water rinse, while extending its retention for at least one hour under continuous rinsing. This durable binding not only serves to strengthen the softening and moisturizing effects of hyaluronic acid, but also to form a flexible polymeric film that, by wrapping around the hair fibers, can protect the hair.

Depending on its molecular weight and formulation, hyaluronic acid has various modes of action : when it is of low molecular weight, it can penetrate to the cortex to reinforce the internal structure, whereas when combined with certain polymers or used at high molecular weight, it forms a protective surface film, thus shielding hair from external aggressors and limiting dehydration.

Note : It is sometimes claimed that hyaluronic acid has the ability to boost hair growth or slow hair loss. However, while hyaluronic acid injections can indeed have this effect, no study suggests that topically applied hyaluronic acid can do the same.

Hyaluronic acid is also beneficial for the scalp, an often-overlooked area.

Just like facial skin, the scalp can be prone to dehydration, for example after too-frequent washes with harsh shampoos. Thanks to its hygroscopic properties, the hyaluronic acid acts like a sponge to retain water in the tissues and restore the scalp’s moisture balance. Moreover, when it has a high molecular weight, hyaluronic acid can form a film on the scalp’s surface, helping to protect it from external aggressors and counterbalance the drying effect of certain surfactants present in shampoos.

Beyond its moisturizing properties, the hyaluronic acid also exhibits interesting anti-inflammatory effects for scalps prone to irritation, redness or itching. Studies in vitro have shown that this molecule can modulate the immune response by acting on certain inflammatory mediators, such as interleukin-8 produced by skin cells under stress. By reducing the release of these cytokines, hyaluronic acid limits local inflammation and soothes sensations of discomfort. Moreover, its strong affinity for the CD44 receptor enables it to inhibit the production of prostaglandin E2 (PGE2) and matrix metalloproteinases, which are also involved in itching sensations and irritation.

To hydrate and soothe the scalp, hyaluronic acid is preferably applied as a serum or lightweight lotion, after shampooing, on slightly damp hair. Moisture enhances its penetration and maximizes its water-retention capacity in the tissues. It is recommended to gently massage with the fingertips in circular motions to ensure even distribution of the product. Some shampoos also incorporate hyaluronic acid to counteract the drying effects of certain surfactants.

When it comes to the hair ends, hyaluronic acid can be applied either before or after washing, depending on supplier recommendations. Most of the time, hyaluronic acid is incorporated into hydrating masks designed for use on towel-dried hair. Combined with film-forming agents, hyaluronic acid also helps smooth the cuticle, thereby limiting water loss and reducing frizz. You can also find it in serums meant for dry hair, as hyaluronic acid is a lightweight, non-greasy active ingredient.

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