Everything to Know About Hyaluronic Acid

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Photo Credits: Rosdiana Ciaravolo / Contributor/ Getty Images | Image Used for Illustrative Purposes Only

A buzzy “it ingredient” with the science to back it up, hyaluronic acid (HA) is a polysaccharide, a form of sugar, that plays a vital role in our bodies. It cushions joints, keeps muscles limber and even helps us see. But, its biggest job is in the skin: Because HA can attract and hold mega amounts of moisture, it’s a critical factor in maintaining hydration levels. “Unfortunately, between the ages of 40 and 50, our skin has lost as much as half of the HA it had at age 20,” says Rahul Mehta, PhD, vice president of R&D at SkinMedica. “Additionally, daily environmental stressors like UV rays and pollution, along with the normal aging process, cause skin to lose its capacity to produce its own HA, leading to dry skin with a rougher texture, as well as fine lines and wrinkles.”

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Cosmetic chemists have had a long-term love affair with HA, adding it to creams, serums and more to pull moisture from the atmosphere and trap it in the skin to hydrate it, giving it a plumper look. “Our bodies are constantly in a battle to stay hydrated, so a hyaluronic acid– rich skin-care regimen is really beneficial,” says Star Walsh, R&D manager of skincare at Johnson & Johnson. And with the launch of the first HA injectable in 2003, doctors have been able to shoot it into achy joints to juice them up, as well as place it in the dermis to turn back the clock. Denser HA fillers, such as Restlyane Lyft and Juvéderm Voluma, placed above the cheekbone can help create the appearance of a moderately lifted face, while a softer HA filler such as Belotero Balance can be used to smooth etched-in wrinkles.

“Hyaluronic acid fillers offer the best of both worlds: They not only attract water and hydrate the skin, but also restore volume while stimulating collagen production, which creates optimal results,” says Wexford, PA dermatologist Debra T. Abell, MD. Recent statistics echo this claim: According to the The Aesthetic Society, more than 720,000 HA filler treatments were performed in the United States last year alone, and the number continues to grow.

Hyaluronic acid comes in many forms, so decoding an ingredient label can be tricky. These are the key terms to know.

What is does the molecular weight of hyaluronic acid mean? 
HA molecules come in two different sizes: low molecular weight and high molecular weight—there are also oligo and nano HA molecules, which are structurally identical and substantially smaller than their larger counterparts. “High molecular weight HA is too large to penetrate the skin, therefore it stays on the outer layer of the epidermis, moisturizing and lubricating it,” explains cosmetic chemist Rhonda Davis. “On the other hand, oligo and nano molecules can penetrate the skin rapidly, reaching its deeper layers to bind moisture and provide intense hydration. This temporarily plumps the skin, diminishing the appearance of fine lines and wrinkles on the surface.”

What does “crosslinking” mean? 
When a product lists HA as “crosslinked” (crosslinking is also used in dermal fillers), it means the chemistry of the hyaluronic acid has been altered by biotechnology to combine several HA fibers and form a lattice-like structure. Uncrosslinked HA is a linear polymer—one long fiber of molecules linked together—and doesn’t provide a lifting effect to the skin. “Think of it as a wire mesh versus a single wire,” says Dr. Mehta. “Uncrosslinked HA may provide hydration quicker than crosslinked HA, but the moisturizing effects don’t last as long.”

Not all HA skin-care products are created equal—here’s the inside scoop on topicals.

Is there a difference between hyaluronic acid and sodium hyaluronate?
Beauty brands often use the terms hyaluronic acid and sodium hyaluronate interchangeably, when, according to Davis, the ingredients are actually two different things. “Sodium hyaluronate is the sodium salt form of HA and is a much smaller molecule,” she says. “Therefore, it’s able to penetrate the skin more easily, making it ideal because it can reach a deeper layer of skin. It also holds up to 1,000 times its weight in water and can reduce transepidermal water loss (TEWL).”

Are serums the most effective hyaluronic acid skin-care formulation?
Davis says most skin-care bases, such serums, creams and sprays, are good delivery systems for HA, but what makes a product great depends on the type of hyaluronic acid used. Chris Caires, chief innovation officer of Perricone MD, says the most effective HA options combine multiple weights of hyaluronic acid in a single formulation, which allows for longer-lasting hydration across the entire layer of skin, and Davis agrees.

Should hyaluronic acid products be applied to damp skin to get maximum benefits?
“Damp skin can accept moisture more easily than dry skin,” says Walsh. “Think of a dry desert: When it rains, water will run right off the surface; when the soil is damp, it accepts the water more easily, just like the skin.” However, HA often works best when formulated with other ingredients, like occlusives—olive oil, jojoba oil and mineral oil, among others—which help seal in all the moisture it draws to the skin. If pure HA is used, another product with occlusive ingredients can be applied on top.

Do they work on all skin types, even sensitive?
According to Dr. Mehta, hyaluronic acid is inert—even high molecular weight varieties—and can work on all skin types. However, several people on Reddit have posted about sensitivities they’ve experienced using HA products. “The only reason for this I can think of is that too much accumulation of high molecular weight HA on the skin’s surface can clog pores in some individuals,” says Dr. Mehta. “Another possible reason could be the presence of non-HA ingredients—such as preservatives or fragrances—in the formulation, which could have caused the irritation. If this does happen, use products that are noncomedogenic to keep pores decongested.”

Recent research shows hyaluronic acid may have antioxidant properties. Is this true?
“In laboratory studies, uncrosslinked low molecular weight hyaluronic acid has been shown to have antioxidant activity that can help fight free radicals, and some topical HA serums claim this as a benefit,” says Nanuet, NY dermatologist Heidi Waldorf, MD. “However, more research is needed to know whether that activity is relevant only to topical products or also heavily crosslinked HA fillers.”

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