With approximately 45 million Google results for “hyaluronic acid skin care,” even the most casual beauty enthusiasts consider themselves experts on the ingredient. They can pronounce it (“HY-uh-luh-RON-ic AS-id"). They can rattle off its basic benefits: It plumps! It fills fine lines! It’s bouncy! They’re aware that hyaluronic acid occurs naturally in the skin (it’s safe!) and attracts 1,000 times its weight in water (it’s hydrating!).

That information is technically true, but as is often the case with a 500-word article, or a 30-second commercial, or a 280-character Tweet, it barely scratches the surface of hyaluronic acid. It’s an oversimplification to the point of misinformation, and an increasing number of aestheticians, chemists, customers, judges, and juries have questions: Where does topical HA come from, if not from within the skin? Where does it get all the water it holds? Do you even want that much water on your face?

Now that it's everywhere and in everything–are we all guilty of misusing hyaluronic acid?

Hyaluronic acid is lots of things. It’s a glycosaminoglycan—somewhat unfortunately known as a GAG—found in the extracellular matrix of almost every cell in your body. It’s a linear polysaccharide. “It‘s a carbohydrate polymer made up of repeating sugar units bound together,” as Aimee Paik, M.D., a board-certified dermatologist with personalized skin care consultation platform Apostrophe, tells BAZAAR. Basically, it’s a sugary carb.

Hyaluronic acid also has lots of names. In its naturally occurring form, inside the body, it was originally known as “hyaluronan,” later renamed “hyaluronic acid.” The synthesized stuff in skincare products is usually “hydrolyzed hyaluronic acid” or sometimes “sodium hyaluronate” (the salt derived from hyaluronic acid). Since the ingredient has all but taken over the beauty space, “hyaluronic acid” or “HA” is used as an umbrella term for any and all types: natural, topical, injectable.

Despite the use of the word “acid,” hyaluronic acid is not an exfoliator. The kind your body naturally produces is a humectant, a healer, a protector, and a plump-er. It controls the water content of the skin—where half the water in your body resides—making skin appear youthful and firm and protecting cells from premature aging. (HA is also found in the eyes and joints.) “You can kind of think of it like a sponge, it soaks up water wherever it is,” says Paik. And yes, the body’s own HA can apparently hold anywhere from 1,000 to 6,000 times its weight in water… but it can only get that water if you drink it or eat water-rich foods.

The majority of the skin’s HA is concentrated in the dermis (the lower layer of the skin), with less in the epidermis (the upper layer of skin), and even less in the stratum corneum (the skin barrier). In fact, hyaluronic acid is only abundant on the skin’s surface in the event of a wound-healing response. “Say you get cut, hyaluronic acid comes and sets off an inflammatory cascade that sends immune cells into the wound that allow repair to occur,” the dermatologist explains. “In its native form, it’s a big molecule, and it’s actually anti-inflammatory.” In other words, HA swoops in to save your skin.

All that hydrating, healing, protecting, and plumping sounds lovely. It only makes sense that you would want to add more of it. That’s just not how skincare works.

Think of it this way: You can’t replenish lost collagen stores by pushing collagen into your face or fortify weak bones with a bit of calcium cream. It’s the same with HA.

Why? Well, for one, hyaluronic acid has a “high molecular weight” in its natural state, making it too large to actually sink into the skin. Cosmetic chemists often hydrolyze or fragment lab-created HA into “low molecular weight” particles to aid in penetration, but these smaller versions can’t make it past the epidermis, either. (“This is why we have the world of injectable hyaluronic acid fillers,” Dr. Greg Altman, a cosmetic chemist and formulator for Silk Therapeutics, points out.)

Two, the hyaluronic acid in skincare is not the same as the hyaluronic acid that naturally occurs in your body.

You’ll be happy to know the HA in over-the-counter and prescription products is not harvested from actual humans (although it was sourced from umbilical cords back in the day). More recently, though, “HA is usually derived from bacterial or microbial fermentation,” Altman tells BAZAAR.

That’s fine, safe, and vegan. The real issue is that much of what we think we know about Hyaluronic Acid: The Skincare Ingredient is based on what we know about Hyaluronic Acid: The Substance In Cells.

The bodily substance is concentrated in the lower layers of the skin; the skincare ingredient sits on top. The bodily substance has a high molecular weight; the skincare ingredient often has a low or very low molecular weight. The bodily substance sources water from your diet; there appears to be no hard data on where the skincare ingredient sources water from. The bodily substance is thought to bind 1,000 times its weight in water; there don’t seem to be any available studies that show the skincare ingredient attracts that amount.

None of the chemists or dermatologists BAZAAR consulted could provide data demonstrating that lab-created, cosmetic-grade HA actually holds 1,000 times its weight in water, although plenty of studies do point to its “significant” water-drawing capabilities. Chemical manufacturer Stanford Chemicals Company states that “topical hyaluronic acid has limited ability to retain water.” A class-action lawsuit recently filed against Peter Thomas Roth alleges the beauty brand falsely advertised its line of hyaluronic acid products by saying the ingredient “will draw moisture from the atmosphere into the user’s skin” and “will hold 1,000 times its weight in water.” With a dearth of research on the subject, a judge has ordered an “in-court demonstration in which a certain amount of hyaluronic acid is placed in a beaker, one thousand times that weight in water is placed in another beaker, and the contents are combined, all watching to see if all the water will be absorbed.”

Although Paik supports the use of HA in general, the dermatologist admits that “smaller HA molecules set inflammation in motion,” referencing the many, many studies that show low molecular weight hyaluronic acid has a pro-inflammatory effect on the skin. “Our bodies are so complicated we don’t quite understand all the signaling that occurs,” she says.

The best available science points to the fact that low molecular weight HA is “able to bind to TLR receptors and consequently initiate the signaling cascade, leading to the production of proinflammatory cytokines and chemokines in various types of cells,” as one study says. In layman's terms, it triggers an unnecessary immune response—a sign that the body is attempting to protect itself from a “foreign invader.”

“Cosmetic companies love to tout that it can penetrate the skin, but most things aren’t meant to penetrate the skin,” says Suzanne LeRoux, the founder and formulator at One Love Organics. Pores are technically outgoing channels for sweat and sebum, and penetration can cause inflammation and irritation.

These marked differences don’t make it a bad ingredient—hyaluronic acid has value as a humectant, if not as a behavioral match for your own HA. Still, the above may help explain why—in this age of hyaluronic-acid-in-everything— people are reporting more adverse reactions to the ingredient.

Editors and Redditors alike have written about the redness and dryness they believe to be caused by topical HA. Instagrammers and influencers have eliminated it from their routines, with impressive results. The Mixed Makeup Facebook group recently held an “HA-free” challenge, with hundreds of comments detailing individual HA sensitivities and reporting improvements. One-star reviews of popular HA serums point to extreme irritation, beauty brands have issued usage warnings for their HA-laced products, one medical-grade HA ointment advises patients that “prolonged use may give rise to sensitization phenomena,” and hyaluronic acid injectables are increasingly associated with late-onset inflammation.

Mary Schook, an aesthetician and cosmetic formulator, is among the first industry professionals to take note of all of the above. “A client had an immediate reaction to something [during a treatment] and I was like, ‘What’s going on here?’” she tells BAZAAR. “The product had three different molecular weights of hyaluronic acid in it.” The incident inspired years of research, trial, and error and today, Schook recommends that her clients remove HA from their routines completely. “I find it to be the one common ingredient that I ask consumers to quit and 98 percent of them have symptoms”—redness, dryness, texture issues, breakouts, dermatitis, rosacea, and more—“that subside.”

So what is really going on?

It’s widely reported that topical hyaluronic acid grabs moisture from the atmosphere and draws it into your skin…but there appears to be no research that proves HA sources water from the environment. “There’s really not a lot of water in the air, even if you lived in a steam room,” Wendy Ouriel, a cellular biologist and founder of Oumere, tells BAZAAR. (Studies confirm that water vapor content ranges from 0.2 percent to 4 percent.) Finding the atmosphere lacking, “hyaluronic acid is going to pull directly from which it’s attached,” Ouriel says: your skin.

“It’s just a basic principle of biology,” the biologist explains. “It’s going to go to the nearest source.” Even in the most humid, tropical, 4-percent-water-vapor conditions, hyaluronic acid will theoretically resort to slurping up the moisture that sits within your skin—and within your own hyaluronic acid stores—and pulling it to the surface. This will temporarily make the skin appear hydrated and smooth, but moisture on the surface evaporates (perhaps why the skin’s innate wisdom prioritizes lower-level moisture), thereby dehydrating the skin (perhaps motivating you to apply more hyaluronic acid, compounding the effect).

“You know when your lips are really chapped and you lick your lips and it feels better for a second, but then 10 minutes later, it’s drier? It’s the same thing,” Ouriel offers. Science supports this: A 2018 study funded by Estée Lauder found that, in humid environments, topical HA "created a false increase in apparent water content exacerbating water loss rate;” meaning, it made skin look hydrated by pulling moisture to the surface, but actually led to dehydration. A 2016 study found that low molecular weight hyaluronic acid (also known as short-chain HA) increased water loss by over 55 percent.

Of course, HA devotees claim you can circumvent this effect by applying the ingredient to damp skin, or by following up with a water-based moisturizer. “Then you’re negating everything,” she counters. “Because it’s just going to absorb the water on your skin, and it’s not going to go into your skin, so what’s the whole point of it?” Eventually, that surface-level water evaporates, leaving no long-term benefit behind.

“Hyaluronic acid is often considered by many as a moisturizer, but in reality, it should strictly be considered a ‘plumper,’” confirms board-certified dermatologist Sheerene Idriss.

That’s not to say HA should be banished to the back of the beauty cabinet, says LeRoux. “I was totally anti-hyaluronic acid, but I’ve been researching this for about a year,” the formulator tells BAZAAR. In that time, she believes she’s cracked the code on non-irritating HA: very small amounts of high-quality, high molecular weight HA. “You can’t use it in too many products, or it will start to draw water from the skin,” she says.

“Not everyone is going to react to HA,” Schook acknowledges, noting that sun exposure, chemical exposure, and the immune system may all play a role in an individual’s response to HA. The aesthetician adds that those with oily skin could have better reactions to hyaluronic acid overall, since oil inhibits one of HA's supposed long-term side effects: microbiome disruption and inflammation (more on that below).

But what about all the hyaluronic acid devotees that swear the ingredient has saved their skin, I ask? To which Ouriel replies, “You can’t determine what ingredient is benefiting your skin unless you eliminate all the other ingredients, and in skincare, you have at least 30 other ingredients [in one routine].”

Paik takes the same-but-opposite approach, pointing out that it’s equally as difficult to determine what ingredient is irritating your skin. “People are using so many things on their skin, and you can blame anything,” she says.

Considering the well-researched relationship between LMW and inflammation, some say high molecular weight, or long-chain hyaluronic acid (HMW HA) is the way to go. But according to Schook, even HMW HA presents a problem.

She points to evidence that all hyaluronic acid may feed a type of fungus that is naturally present on the skin’s surface: microorganisms on the microbiome called dermatophytes. “We have fungi that lives on our skin that thrives on sugar, and HA is a sugar,” says Schook. “Once the fungi ingest the sugar, they secrete an enzyme that breaks down our skin's barrier that allows bacteria and viruses to invade, creating inflammation.”

The formulator explains that “the wetter the skin, the easier the invasion for the dermatophyte,” and any hyaluronic acid of any molecular weight essentially holds water on the skin’s surface. “In the world of wound healing, when you keep the skin wet too long, it is called maceration,” she says. “Maceration causes bacteria and viruses to invade, thus inflammation.” (True, other humectants create “wet” skin, too, like glycerin. But “glycerin acts as a natural antifungal,” Schook explains, negating that whole fungus-feeding thing.)

It’s worth noting that although HMW HA is anti-inflammatory, it still triggers an immune response when applied topically. The skin essentially recognizes it as part of the body’s natural wound-healing mechanism and gets to work. It can be useful in the “setting of acute wounds to initiate healing,” says Paik.

"I see many patients who are overusing it in multiple steps of their skincare regimen, and this is ultimately leading to dehydration,” confirms Idriss. “I recommend limiting its use to every once in a while if you want a plumping effect, but if you can’t part ways with your daily HA, then stick to having it in only one step (or product) of your routine."

Of course, you could always boost your body’s own supply. “My take is, why put hyaluronic acid in your skincare in the hope that maybe you’ll get the hydration?” says Ouriel. “Why not just have your body make its own hyaluronic acid, and preserve the hyaluronic acid that your body already makes?”

The main way to make more hyaluronic acid is to increase cellular turnover, since each new cell begets a new extracellular matrix, complete with its own HA. “Use AHA, BHA, and PHA exfoliation to stimulate your body to make more naturally, which can be done indefinitely,” the biologist recommends. (Daily gua sha facial massage stimulates cellular turnover, too, without all the exfoliation.) You can also get hyaluronic acid via food, like sweet potatoes and bone broth.

Finally, help the hyaluronic acid you already have by giving it more moisture to hoard. Chug a glass of water (or eight). Snack on water-rich veggies like celery and cucumber. Your naturally-occurring HA—the real “miracle ingredient,” heavy with hydration and snuggled deep within your dermis—will thank you.

Jessica DeFino is a beauty reporter covering natural, holistic, sustainable skincare. Her work has appeared in _Vogue, Harper's BAZAAR, Allure, New York Magazine's The Cut, and more. She is currently working on her first book