Find out whether the trendy skin-care ingredient is worth adding to your hair-care routine, too.

Hyaluronic acid is an all-star skin-care ingredient praised for its ability to lock moisture into skin and produce a dewy, healthy complexion. Previous research even suggests hyaluronic acid may, from the inside out, help correct premature skin aging that occurs from ultraviolet (UV) exposure.

Recently, some users on TikTok have begun gushing about hyaluronic acid for another reason: its purported ability to transform hair from dry and brittle to healthy and lustrous.

"Saw a TikTok that said hair oil doesn't moisturize your hair, only water can. So I tried Hyaluronic Acid!" wrote TikTok influencer Kaitlyn Boyer in an August 2021 video that has been viewed over 3.7 million times. Starting out with damaged-looking locks, she explains that she wet her hair and applied a hyaluronic acid product, The Ordinary's Hyaluronic Acid 2% + B5, nightly. After one night, her hair looks noticeably healthier, and after two nights, she notes a "major difference." At the two-week mark, she claims her hair to be "way more manageable,” revealing that even her hairstylist asked what products she had been using.

Muneeb Shah, DO, a fourth-year resident physician at Campbell University in Buies Creek, North Carolina, and social influencer who goes by “Derm Doctor” on TikTok, endorsed Boyer’s claims in a viral video that has more than 10 million views. “Hyaluronic acid is a powerful humectant, meaning it holds onto about 1,000 times its weight in water,” he said, calling it “an amazing moisturizer for hair and skin.”

Should you be using hyaluronic acid in your hair, too? Here’s what experts want you to know.

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New York City–based Daniel Belkin MD, a board-certified dermatologist and dermatologic surgeon at New York Dermatology Group, echoes Dr. Shah, saying that a hyaluronic acid molecule can bind up to 1,000 times its weight in water, “so it is a very powerful humectant — a molecule that draws in or retains hydration.”

Board-certified dermatologist Joshua Zeichner, MD, associate professor and director of cosmetic and clinical research department of dermatology at Mount Sinai Hospital in New York City, says hyaluronic acid is a staple in skin care, but he’s seen it increasingly used in hair-care products lately.

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Each hair strand consists of layered proteins including keratin filament, as well as structural components such as matrix macrofibril, cortex, and finally cuticle scales, which are organized in a row, says Ava Shamban, MD, a board-certified dermatologist based in Los Angeles.

Healthy, vibrant, and shiny hair strands have smooth, flat cuticles and moisture is sealed in, Dr. Shamban says. On the other hand, in the case of damaged or dull-looking stands, the hair shaft is dehydrated and the overlying scales are elevated, giving hair a brittle texture. Hair is porous, and overwashing, frequent heat application such as from blow-drying, and environmental factors can cause damage.

When applied to the hair, hyaluronic acid “attracts moisture from the environment and pulls it into the hair, holding onto it — like water soaking into a sponge, it expands,” Shamban explains. “It fights frizzing, and helps to retain and maintain the proper balance of moisture proteins and lipids needed for healthy hair.”

Dr. Zeichner agrees that there are multiple benefits of adding the serum to your locks. “It can help soften, hydrate, and plump the hair shaft itself,” he says. “This means softer-, fuller-appearing hair.”

And, because it is already established as a great skin-care ingredient, hyaluronic acid is also great for the scalp, Shamban points out. “Often we don't treat the scalp as dermis, but it is skin,” she says. The biggest difference between the scalp and the rest of our skin is that the scalp has thousands of terminal hair follicles, which grow hair strands. The scalp also has a greater sebaceous network than the rest of the skin. Shamban says this network is similar to a subway system in function with passageways to deliver and deposit oil, which is used for skin nutrition to coat, moisturize, soften, and protect.

Los Angeles-based celebrity hair colorist Tracey Cunningham explains that she is seeing a “skinification of hair,” which includes using skin-care ingredients like hyaluronic acid in hair-care products. “Finally, clients are starting to realize that they need to treat their hair similar to their skin for optimum hair health, especially if you color or use any chemical services or hot tools regularly,” she explains. In addition to hyaluronic acid, ceramides and glycerin are being added to hair-care products to deeply repair and moisturize strands, she notes.

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Dr. Belkin and Shamban say hyaluronic acid is safe to use on skin and hair alike.“Since it is a naturally occurring molecule in the human body, it cannot cause allergy,” Belkin explains, “nor does it cause irritation.”

Products with hyaluronic acid are good for all hair types, says Cunningham. “Normally found in skin-care products, hyaluronic acid helps to deeply moisturize the hair just like they do the skin. After all, the scalp is an extension of the skin, and the healthier the hair looks, the better it looks when it's styled,” she explains.

Indeed, hyaluronic acid can be used across all hair types, even those with sensitive, brittle, or chemically treated hair, says Zeichner.

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Belkin recommends applying hyaluronic acid to moist washed hair, which allows the ingredient to bind properly. This will act similarly to a hair oil or leave-in conditioner “that has more occlusive-type moisturizers (oils, waxes) will help lock in moisture,” he says.

While a hyaluronic hair product will likely cost you less, a skin-care product with the ingredient on hand will work on your hair, too. “There is not necessarily a strict distinction in the formulation of hair care versus skin care, so depending on the specific product, I don't think it would be an issue to use a skin-care product in the hair, especially if it were a relatively pure formulation of hyaluronic acid,” Belkin says.

To try the trend, Belkin suggests Oribe Power Drops Hydration and Anti-Pollution ($58, Oribe.com), while Cunningham recommends Olaplex No. 8 Bond Intense Moisture Mask ($28, Sephora). “It contains high-quality hyaluronic acid to weightlessly moisturize the hair, along with their proprietary, patented bond-building technology to repair and strengthen strands for healthier hair,” she explains.

If you want a double-tasking product, Belkin recommends The Ordinary Hyaluronic Acid 2% + B5 ($6.80, Ulta.com), La Roche-Posay Hyalu B5 Pure Hyaluronic Acid ($29.99, laroche-posay.us), and, if you are looking to splurge, SkinMedica HA5 ($120, SkinMedica).

RELATED: 10 Surprising Causes of Dry Skin

All three experts encourage adding hyaluronic acid serum to your hair-care routine, whether by opting for a hair product with the ingredient or repurposing a hyaluronic acid skin-care product for your hair. “This TikKok trend is fact not fiction, which is not always the case,” says Shamban. “All in all, it is great for youth-ifying the hair.”

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