Article Summary

What is hyaluronic acid?
Hyaluronic acid in skincare
Types of hyaluronic acid
Hyaluronic acid myths and truths

The Science Behind Hyaluronic Acid

Hyaluronic acid. One of the most popular ingredients in skincare yet often misunderstood.

We’ve sifted through all the claims, myths, and most importantly the science to bring you this deep dive on one of skincare’s most popular ingredients.

Learn how hyaluronic acid works, what to look for in products, and how to actually use it. And as always, we’re debunking the myths and getting to the truth behind hyaluronic acid.

What is Hyaluronic Acid?

Hyaluronic acid is a type of carbohydrate called a polysaccharide, a long chain of sugars. It’s specifically categorized as a mucopolysaccharide which lets us know a few things: it’s naturally occurring in the body, it’s made of repeating disaccharide units, and each unit will be composed of an amino sugar and an uronic acid.

Imagine you’re putting beads on a string. A polysaccharide is going to be a really long one and the beads will be in a pattern. The building blocks of hyaluronic acid are n-acetyl glucosamine and glucuronic acid, two sugars that form the repeating disaccharide units of its chain structure. If the blue bead is n-acetyl glucosamine and the purple one is glucuronic acid then we will basically alternate those beads until we’ve got a string of them.

When we have a full chain of “beads”, this is referred to as High Molecular Weight Hyaluronic Acid (HMW HA). We can also chemically chop up this chain into smaller fragments to create Low Molecular Weight Hyaluronic Acid (LMW HA) fragments. HMW HA is a large molecule and has less penetration into the skin as a result while LMW HA penetrates deeper and seems to have more physiological effects, stimulating skin defenses and helping regulate inflammation.

As we discussed, hyaluronic acid is naturally found in the body - this form is called endogenous hyaluronic acid. While it does a number of cool things inside our skin, this doesn’t actually mean that you can apply a hyaluronic acid product on top of your skin and expect it to do the same. So while being a “skin identical” ingredient means hyaluronic acid is unlikely to cause a reaction, it’s important to look at exogenous hyaluronic acid (the stuff in your products that isn’t synthesized by our skin) and its benefits separately.

The structure of hyaluronic acid can actually tell you a lot about what this ingredient is used for in cosmetics. The amine and hydroxyl groups let us know that this molecule is able to participate in something called hydrogen bonding3. Like other humectants, this allows hyaluronic acid to grab onto H2O molecules (water) and keep them within our skin so they don’t evaporate.

Hyaluronic Acid in Skincare

Hyaluronic acid is really just a humectant. As we just touched on, humectants are great ingredients for helping hydrate the skin because they attract water and keep it inside the skin.

As we’ve discussed in previous blogs on the skin barrier and dehydration, our skin barrier is responsible for keeping water in the skin. Trans epidermal water loss (TEWL) is the term used to describe the diffusion and evaporation of water from the skin surface and any barrier impairment will increase TEWL, causing dehydration.

Benefits of Rehydrating the Skin

improves skin appearance by changing how light interacts with the skin and temporarily plumping things up
increases the activity of the enzymes that dissolve the “glue” between dead skin cells, allowing them to shed more easily
reduced inflammation associated with dry skin and barrier impairment
helps increase the rate of repair and overall wound healing in the skin
improved the flexibility the skin barrier and allow it to function better

Humectants serve an important role in skincare products but they’re helper ingredients. Think of them as the supporting cast, not the star of the show. Despite hyaluronic acid popping up in many “anti-aging” serums, its benefits mainly stem from improved skin hydration. Don’t expect it to take away your dark spots or do more than temporarily soften fine lines and the appearance of pores by plumping up the skin.

Important: hyaluronic acid is not exfoliating. While exfoliants are often referred to as “acids,” they’re actually usually carboxylic acids. Acids (and bases) are a very broad category in chemistry that just tells you if a molecule accepts or donate electrons.

Types of Hyaluronic Acid

Almost all hyaluronic acid in skincare is sodium hyaluronate, the more stable salt form of hyaluronic acid. It does come in different molecular weights but all of them are just listed as “sodium hyaluronate” on the ingredient list. The exception is some of the new and interesting forms of hyaluronic acid popping up, especially in K-Beauty.

High Molecular Weight Hyaluronic Acid (HMW HA) has film forming properties like most polymers that allow it to seal in moisture in addition to being a humectant. Because it grabs onto water in solution and forms molecular networks, it can act as a thickener in serums but only forms a weak gel on its own.

Low Molecular Weight Hyaluronic Acid (LMW HA) is just fragments of the high molecular form and you’ll usually see it listed as “sodium hyaluronate” too or sometimes hydrolyzed hyaluronic acid. It loses the film filming properties of HMW HA but you get more penetration into the skin, it usually doesn’t influence the texture of a product, and some studies suggest that it’s able to reduce skin inflammation by ramping up skin defenses.

Hyaluronic Acid Derivatives. There are too many to list but many of the derivatives have been altered to address the potential shortcomings of hyaluronic acid.

Sodium acetylated hyaluronate has replaced the hydroxyl groups in HA with acetyl ones, allowing it to not only better penetrate the skin but stay within the skin longer.
-Hydroxypropyltrimonium hyaluronate is a positively charged form that can penetrate the negatively charged skin barrier even in wash off products like cleansers, leaving more hyaluronic acid in the skin than the regular kind.
Sodium retinoyl hyaluronate needs further study but this water of HA and retinoic acid may offer a gentler alternative to tretinoin.

Crosslinked hyaluronic acid has been utilized for many years in hydrogel wound dressings and injectables as crosslinking helps create a more stable gel. It’s now popping up in skincare since it’s less resistant to breakdown by the skin.

Finding the Right Product

Because it’s such a popular skincare ingredient, skincare brands have started to include it in most of their new product launches. While skin hydration is helpful for all the reasons we’ve discussed, don’t feel like you need to go out of your way to use hyaluronic acid. If you check the ingredients of your current products, chances are it’s already in there somewhere.

Hyaluronic acid is an effective humectant and an ingredient that is well tolerated by even sensitive skin types. If you’re interested in using hyaluronic acid, we suggest looking for it in products where it really shines - which is behind the scenes as a supporting player, not the star.

Moisturizers are emulsions made from combining oil and water phases. Because their primary function is to trap water and increase hydration, they’re most effective when they include occlusive agents and emollients alongside humectants like hyaluronic acid. This allows you to hydrate, trap moisture, and also support barrier health.

Example: Stratia Skin Interface Peptide Cream

Serums are usually water based so they’re the perfect vehicle for water-soluble humectants like hyaluronic acid. The concerns they target will vary but for hydration purposes, look for hyaluronic acid paired with other humectants. Glycerin, a workhorse ingredient, rehydrates dry skin that is deficient in the channel proteins into the skin. Ceramide promoters like niacinamide or hyaluronic acid precursors like n-acetylglucosamine also help address hydration over time alongside the immediate effects of HA.

Example: Stratia Skin Rewind

How to Use Humectants

If you consume skincare content online, it’s easy to feel intimidated when it’s time to actually use your products. It seems like there’s a new “rule” every week on how you need to use it and it can get overwhelming. We’ll debunk some of these myths in a second but luckily, the evidence doesn’t indicate any special precautions are needed and hyaluronic acid can be used the same as any other humectant.

Here’s what to keep in mind:

Order. While we often hear about how hyaluronic acid should go before this ingredient or after that one, it’s actually all about what product it’s in. Just follow our product order guide and layer it according to whether it’s in a serum or moisturizer.

Climate. No special climate or season is needed to use HA as there’s plenty of water in the skin that humectants can trap there - and hyaluronic acid has still been effective in low humidity, alpine desert environments. Keep reading for more on this myth.

Skin Prep. There’s a lot of debate on whether hyaluronic acid should be applied to wet or dry skin. As we discussed, humectants really keep the skin’s own water from evaporating so adding additional water isn’t needed - and there’s water in the product itself too. Use whichever method you like best.

Hyaluronic Acid Myths and Truths

It wouldn’t be a blog on hyaluronic acid without addressing the elephant in the room: the myths circulating around hyaluronic acid. Here’s some of the most common ones and if the evidence checks out.

Myth #1: hyaluronic acid pulls water from your deeper skin layers and dries you out

This one seems reasonable until you look at how humectants work. Remember the hydrogen bonding we discussed early? Because this requires that the water molecules be in close proximity, hyaluronic acid will have no influence on water that is in the dermis.

The water hyaluronic acid grabs onto isn’t stolen from the skin either. Most of the water in the skin barrier is already bound by the skin’s own humectants and therefore not available. Think of hyaluronic acid as a girl’s girl. - it’s not out here looking to steal someone’s partner, it waits until it sees someone available. Free water is normally lost during TEWL (trans epidermal water loss) and HA instead keeps it in the skin.

It’s a shame that hyaluronic acid can’t draw water from the deeper skin. The dermis is rich in water, holding about 60-70% of the skin’s water. Because this tissue is vascular (has blood supply), it’s easily rehydrated where the epidermis has to rely on diffusion from the dermis. Since dehydration is really only a concern within the skin barrier, it would be nice if we could redistribute water to where it’s needed.

These reasons are also why applying on damp skin is optional. Dry skin types may also need occlusive and emollient ingredients but humectants can be used on their own as well.

Bottom line: there are no quality studies showing that hyaluronic acid skincare makes you more dehydrated. The evidence actually demonstrates the opposite.

Myth #2: sodium hyaluronate is the “cheap,” synthetic version of hyaluronic acid and a smaller molecule.

Pretty much all of the hyaluronic acid in cosmetics is sodium hyaluronate, regardless of whether a brand calls it hyaluronic acid or not. Since it’s the only option, it’s not the cheap option.

Sodium hyaluronate is actually what is primarily found in the body since hyaluronic acid becomes sodium hyaluronate at physiological pH6 and most l parts of the body are in this 7.35-7.45 range.

In terms of size, this salt form of hyaluronic acid is sold in various molecular weights from the HMW HA discussed to medium weight HA and different LMW HA weights. Just like naturally occurring HA, it varies in size.

Myth #3: low molecular weight hyaluronic acid causes inflammation

It’s true, low molecular weight hyaluronic acid fragments are produced during the inflammatory stage of wound healing and involved in inflammatory processes. But this seems to have been taken a step further and used to imply that LMW HA causes inflammation.

Inflammatory cellular processes are continually occurring, they’re used to maintain and repair our body. It’s important not to see the word “inflammatory” and assume the worst. This is different from chronic or acute inflammation where you have either ongoing or very high levels of inflammation that interfere with the function of the skin.

The studies used to suggest that LMW HA is inflammatory, like this one, are only about the hyaluronic acid that is inside our body and don’t establish that it’s harmful. You can’t look at endogenous hyaluronic acid (reminder, the stuff inside our bodies) and say that topical products will do the same.

Bottom line: there is no evidence at this time to show that hyaluronic acid is detrimental to the health of our skin when used in skincare. A few studies even found that topical LMA HA reduced inflammation in patients with seborrheic dermatitis and rosacea.

Myth #4: hyaluronic acid needs to penetrate deeply to work.

Products that market themselves as “medical grade” will often claim to use higher concentrations of ingredients, fancy delivery systems, and special ingredients that are smaller in wise. But medical grade isn’t a regulated term and the only true medical grade skincare is prescription.

The truth is, many skincare ingredients don’t get deep into the skin and still work just fine. “As deep as possible” is not the goal but rather reaching where they’ll work best. While retinoids like tretinoin penetrate into the dermis, allowing them to aid in the production of new collagen, hyaluronic acid actually isn’t needed that deep. The dermis is full of water already, it’s the skin barrier that can lack water.

Bottom line: the amount of penetration needed for ingredients depends on where in the skin they work best.

References

Mira is a skincare educator, blogger, and the content creator behind Skin Science by Mira and The Skincare Forum on Facebook. While skincare keeps her busy, she’s also pursuing her degree in Nursing and loves to spend her free time hiking. As a content writer for Stratia Skin, Mira shares her evidence-based approach to skincare topics and a passion for making science accessible.

The Power of Hyaluronic Acid: A Scientific Breakdown