Hyaluronic Acid in Skincare Explained: What It Is and How It Works

Somehow, Hyaluronic Acid has become skincare’s default answer for anything that looks a bit dry, tired, or vaguely unhappy. Every serum, every moisturiser, every face cream – if it doesn’t have Hyaluronic Acid in it, the brand’s probably gone bust. It is the ingredient widely marketed for its ability to plump skin, erase wrinkles, and generally make you look like you’ve had eight glasses of water when, really, you’ve barely managed a coffee.

But what exactly is Hyaluronic Acid, and does it genuinely have any effect, or is it merely smoke and mirrors?

Spoiler alert: it’s actually one of the few buzzy ingredients that isn’t complete rubbish. So grab a coffee (or water, since we’re talking hydration), and let’s break down what Hyaluronic Acid actually is in plain language, what it genuinely does, and whether you should bother with it.

What on Earth is Hyaluronic Acid?

The Science: What It Actually Is

First things first: the name’s misleading. Despite being called an “acid”, it doesn’t work like other skincare acids such as Salicylic Acid, Glycolic Acid, AHAs, or BHAs. Those acids exfoliate the skin. Hyaluronic Acid doesn’t do this. The word “acid” in the name just comes from one of its component sugars, not from how it actually behaves on skin.

Technically speaking, Hyaluronic Acid (HA), also known as Hyaluronan or Hyaluronate, is a substance composed of sugar and amino acid building blocks, making it what scientists call a glycosaminoglycan.

In Plain Language: Where It Lives in Your Body

In plain terms, it’s a sugar molecule that occurs naturally in your body: in your skin, eyes, joints, blood, saliva, and the fluid around your gums. It acts as a lubricant and cushion, keeping tissues bouncy and helping fluids move properly throughout your body.

Hyaluronic Acid is present throughout human tissues, but it is most concentrated in the skin, the vitreous humour of the eye, synovial fluid in joints, and the umbilical cord. Approximately 50% of the body’s total Hyaluronic Acid is located in the skin, making it the single largest reservoir of this molecule.

A Bit of History (But Keep It Brief)

Hyaluronic Acid was first isolated in 1934 by Karl Meyer and John Palmer at Columbia University, who extracted it from the vitreous of bovine eyes. The name derives from the Greek word “hyaloid” (meaning “vitreous” or “glass-like”) combined with “uronic acid”, one of its component sugars.

What It Does in Your Body

In your body, Hyaluronic Acid has several important jobs. It helps keep your skin elastic and plump, provides cushioning for your joints, supports wound healing, and helps fight inflammation. Because it has a gooey, slippery texture, it helps keep tissues bouncy and helps fluids move properly throughout your body.

How Hyaluronic Acid Works in Your Skin

The Mechanism: Water Retention

The primary function of Hyaluronic Acid in the skin is water retention. One gram of Hyaluronic Acid can hold up to six litres of water – that’s about 1,000 times its own weight. A person weighing about 70 kg has about 15 grams of Hyaluronic Acid in their body, of which 5 grams are replaced daily.

When you use Hyaluronic Acid products on your skin, they work by covering the top layer and preventing water loss, which acts like a moisturiser. This protective layer makes your skin appear softer and feel smoother to the touch.

Key Benefits for Your Skin

So it holds water. But what does that actually mean for your skin?

• Intense Hydration: The main job of Hyaluronic Acid in your skin is to keep it moist and healthy. Dehydrated skin looks dull and tired. It can happen to anyone, regardless of whether your skin type is oily, dry, or combination. HA provides hydration by holding water in the space between your skin cells, making your skin look plump and smooth.
• Plumping Effect: Dehydrated skin makes fine lines and wrinkles appear more prominent. HA hydrates the skin, creating a plumping effect. It literally puffs up skin cells, smoothing the surface.
• Better Texture: Hyaluronic Acid helps improve elasticity, making skin feel firmer and more supple. If you’re dealing with rough patches or uneven texture that makes the foundation look patchy, adding hydration can make a big difference. It creates a smoother base, so your makeup sits better.
• Healing Support: HA isn’t just about appearance; it supports skin health. Research shows it plays a role in wound healing by helping regulate inflammation and promoting blood vessel formation. If you’ve overdone it with retinol or damaged your skin barrier with harsh scrubs, HA is a gentle way to help your skin recover.

The Reality Check: It’s Temporary

As you age, your body makes much less Hyaluronic Acid – it drops to only about 5% of what you had when you were younger. This decrease leads to drier, less elastic skin, causing wrinkles and fine lines to form. Using Hyaluronic Acid products can help replace what your body has lost and improve your skin’s hydration and appearance. However, the effects require continuous application. The half-life of HA in skin is less than 24 hours, meaning exogenously applied HA breaks down rapidly. Any benefits cease when the application stops.

Types of Hyaluronic Acid in Cosmetics: Why Molecular Weight Matters

Skincare products contain different sizes of Hyaluronic Acid molecules that work in different ways. Small molecules can penetrate deeply into your skin to reduce wrinkles, while large molecules remain on the surface to create a protective barrier and prevent water loss.

• Low-Molecular-Weight HA (5 – 300 kDa): Low-molecular-weight Hyaluronic Acid has very small molecules that can penetrate more deeply into your skin by crossing the outer layers. This type helps prevent ageing by making skin brighter, more hydrated, and firmer while reducing wrinkles and restoring volume. It’s especially good for anti-ageing because it can promote collagen production and improve skin elasticity.​
• Medium-Molecular-Weight HA (300 – 1,000 kDa): Medium-molecular-weight Hyaluronic Acid offers a balance between penetrating the skin and retaining moisture on the surface, making it ideal for improving skin texture and elasticity.​
• High-Molecular-Weight HA (>1,000 kDa): High-molecular-weight Hyaluronic Acid has large molecules that mainly work on the surface of your skin. It creates a protective barrier that prevents water loss and acts as a powerful antioxidant that fights against harmful substances. This type is perfect for providing long-lasting hydration by forming a film on your skin’s surface.

Why “Smaller” Isn’t Always Better

A 2023 study examining 12 different Hyaluronic Acid molecules found that penetration efficiency was proportional to molecular weight – smaller molecules penetrated more readily. HA with weights under 80 kDa showed the highest dermal penetration (63 – 78%), while larger molecules exhibited significantly lower absorption.​

However, smaller is not automatically better. Low-molecular-weight HA fragments (<400 kDa) can trigger inflammatory responses and are recognised by the body as “danger signals”. High-molecular-weight HA suppresses inflammation. The size of HA fragments determines whether they signal damage and initiate immune responses or provide anti-inflammatory, tissue-protective effects.​

The optimal approach in topical formulations appears to involve combining multiple molecular weights to achieve both surface hydration and deeper penetration. Some newer products use branched Hyaluronic Acid, which combines smaller and larger pieces to deliver the benefits of both while making the product less thick and sticky, making it easier to use in creams and serums.

What to Look for on the Label

Look for products containing multiple molecular weights. Formulations with both high- and low-molecular-weight HA address surface hydration and deeper penetration simultaneously. Single-molecular-weight products provide more limited benefits.

Why Hyaluronic Acid Works… And Its Limitations

Why It’s So Effective

Hyaluronic Acid is so effective because it’s already a natural part of your body’s structure and works with your existing biological systems. Since your body recognises it as a natural substance, it doesn’t cause reactions or problems when used in skincare products.

What makes Hyaluronic Acid special is that it does many different jobs at the same time. It works as a cushion and lubricant for your tissues, helps your body respond better to injury, and provides deep hydration while protecting against water loss. It also has anti-inflammatory and antioxidant properties, which help fight harmful substances that can damage your skin and cause ageing.

Hyaluronic Acid also works at the cellular level by supporting key skin processes, including cell growth, movement, and healing. It stimulates your skin to produce more collagen through specific biological pathways, helping improve your skin’s structure and firmness.

What It Definitely Won’t Do

Setting realistic expectations requires acknowledging limitations.

HA cannot reverse structural skin ageing. Collagen degradation, elastin loss, cellular senescence, and photoaging involve processes beyond hydration. While HA may support collagen synthesis indirectly, it doesn’t replace lost collagen or repair damaged structural proteins.​

Topical HA doesn’t permanently increase the skin’s natural HA content. HA cannot prevent molecular ageing processes. Glycation, oxidative stress, mitochondrial dysfunction, and accumulated DNA damage in skin cells continue regardless of topical hydration. HA may reduce oxidative damage to some degree, but it’s not an anti-ageing panacea.

The ingredient works as a humectant and temporary hydrator. In low-humidity environments, HA may draw water from deeper skin layers to the surface, potentially contributing to transepidermal water loss rather than preventing it.

Marketing claims that topical HA can produce “injectable-level results” are misleading. Applying HA topically cannot achieve the same volumising effects as cross-linked HA fillers injected into the skin, as their mechanisms and results are fundamentally different.

Hyaluronic Acid and Skin Ageing

The most striking change in ageing skin is the near-complete disappearance of epidermal HA, while dermal HA persists but becomes less extractable. Why this happens isn’t fully understood, but the epidermis loses the primary molecule responsible for binding and retaining water, resulting in moisture loss.​

The body’s production of Hyaluronic Acid declines with age. This decline can begin as early as the twenties, and by the ages of 40 – 50, approximately half of the skin’s endogenous HA may be lost. This reduction affects both the epidermis and dermis.

Several changes occur as HA levels decrease:​

• Reduced Water Content: Less HA means less water retention, leading to drier, less supple skin.​
• Decreased Elasticity: The structural support provided by the HA-water gel diminishes, contributing to loss of skin turgor.​
• Visible Signs of Ageing: Fine lines, wrinkles, and a rougher skin texture become more apparent as the skin’s moisture-binding capacity declines.​

UV exposure accelerates these changes. About 80% of facial ageing is attributed to UV radiation. Initially, UV exposure triggers enhanced HA deposition as part of a wound response. But repeated, extensive UV exposure ultimately leads to scar-like collagen deposition rather than the normal collagen mixture that provides resilience.

What Clinical Studies Actually Show

Clinical research on topical Hyaluronic Acid provides reasonably consistent evidence for hydration benefits, though the magnitude varies depending on formulation, molecular weight, and study design.

• 6-Week Study (40 women aged 30 – 65): Twice-daily application of an HA serum produced a 134% increase in skin hydration immediately after application, 55% sustained hydration increase at week 6, 64% improvement in smoothness, 63% improvement in hydration perception, 31% improvement in fine lines, 14% improvement in wrinkles, and high tolerability with no significant adverse effects.​
• 12-Week Study: An HA-based serum showed improvements in facial skin texture (79%), lines and wrinkles (50%), and skin tone (44%).​
• Multi-Weight HA Formulations: Research on formulations combining low-, medium-, and high-molecular-weight HA demonstrated significant improvements in moisturisation within 30 minutes of application, with clinical improvements in dryness, roughness, and fine lines observable at 2 weeks.​
• Dermal HA Increase: A study using facial swabbing found that HA levels in the dermis increased after topical serum use – not simply due to residual product on the surface, but suggesting a stimulating effect on endogenous HA production.

Where Hyaluronic Acid Comes From: Production and Safety

How It’s Produced

Industrial production of Hyaluronic Acid uses two main methods: extraction from animal tissues or microbial fermentation.​

Historically, HA was extracted from rooster combs, which contain high concentrations of HA. This method requires extensive purification to remove proteins, endotoxins, and potential pathogens. Yields are limited by raw material availability.​

Microbial fermentation now dominates commercial production. Streptococcus zooepidemicus, a pathogenic bacterium, naturally produces HA as part of its extracellular capsule and can generate yields up to 7 g/L under optimised conditions. However, using pathogenic organisms requires rigorous purification protocols to ensure product safety.​

To address pathogen concerns, researchers have developed genetically modified non-pathogenic organisms for HA production. Engineered strains of Bacillus subtilis, Escherichia coli, Corynebacterium glutamicum, and Lactococcus lactis can produce HA. A genetically modified Corynebacterium glutamicum strain achieved HA production of 71.4 g/L.​

For cosmetic applications, bacterial fermentation-derived HA is functionally identical to animal-derived or naturally occurring HA. The molecular structure is the same regardless of source.​

How Safe Is It?

Hyaluronic Acid is one of the safest skincare ingredients available, primarily because it is a substance the body naturally produces.​

The Cosmetic Ingredient Review Expert Panel conducted comprehensive safety assessments and concluded that Hyaluronic Acid, sodium hyaluronate, and potassium hyaluronate are safe as cosmetic ingredients at concentrations up to 2%. The evaluation included acute, short-term, and chronic toxicity studies across multiple species and exposure routes. No reproductive, developmental, or genotoxic effects were found.​

Adverse reactions to topical HA in cosmetic concentrations are exceptionally rare. The vast majority of reported adverse events involve injectable HA fillers for medical or aesthetic purposes, not topical application. Injected HA carries different risks, including vascular occlusion, tissue necrosis, and inflammatory reactions, which are not relevant to topical cosmetic use.​

One consideration: HA molecular weight may influence safety in susceptible individuals. Low-molecular-weight HA can trigger inflammatory responses through TLR activation, though this primarily occurs at concentrations and in contexts not typical of cosmetic use. Some formulations deliberately avoid very low-molecular-weight fractions to minimise pro-inflammatory potential.​

Regulatory bodies, including the Cosmetic Ingredient Review (CIR) Expert Panel and the European Union Cosmetics Regulation, have approved HA from both animal and microbial sources for cosmetic use, provided products meet purity and safety standards.

How to Use Hyaluronic Acid Products

Application technique affects how well HA performs. Because Hyaluronic Acid is a humectant that draws moisture from its surroundings, the environment and layering sequence matter.

• Apply to Damp Skin: Most guidance suggests applying HA to slightly damp skin (not wet, not dry) to provide immediate moisture for the molecule to bind. However, recent testing suggests that the damp vs. dry application makes less of a difference than ensuring the HA is sealed with a moisturiser afterwards.​
• Always Apply a Moisturiser or Occlusive: This step is critical. Without a sealing layer, HA in low-humidity environments may draw moisture from deeper skin layers rather than from the air, potentially leaving skin feeling tight or dry. Applying a moisturiser on top locks in hydration.​
• Effective Concentration: More Isn’t Better: Clinical evidence suggests concentrations between 0.1% and 2% are effective. Higher concentrations (5 – 10%) are not necessarily more beneficial and can create an unpleasant gel-like texture.​
• Frequency and Compatibility: HA can generally be used twice daily, morning and evening, and is compatible with most other skincare ingredients, including retinol, vitamin C, and AHAs/BHAs. The ingredient pairs well with other actives. HA doesn’t interfere with retinoids, vitamin C, niacinamide, or peptides. It provides hydration that can buffer potential irritation from stronger actives.​
• Packaging Matters: Stability matters. HA can break down in formulations containing free-radical-generating ingredients or when exposed to light and air. Opaque, airtight packaging better preserves actives.

Who Needs Hyaluronic Acid (and When Not to Expect Miracles)

Who Benefits Most

• Dry or dehydrated skin: If your skin looks dull, feels tight, or your makeup sits unevenly, HA provides immediate and sustained hydration.​
• Using strong actives: If you’re using retinol, AHAs, BHAs, or other potentially irritating ingredients, HA helps soothe and hydrate without interfering with their function.
• Dry climates or environments: Offices with air conditioning, aeroplanes, winter heating – anywhere that sucks moisture from your skin benefits from HA layered under an occlusive.

Who Shouldn’t Expect a “Wow” Effect

• Pigmentation, acne, or scarring concerns: HA hydrates but doesn’t address pigmentation, breakouts, or textural scarring on its own. You’ll need other actives.​
• Expecting filler-level volume: Topical HA cannot replicate the volumising effects of injected HA fillers. The mechanisms differ fundamentally.

Final Thoughts

Hyaluronic Acid is a genuinely effective hydrating ingredient backed by substantial research. It improves skin moisture and barrier function and can reduce the appearance of fine lines by plumping the skin. These are documented, measurable effects.​

What it cannot do is reverse deep wrinkles, rebuild collagen on its own, or substitute for sun protection – the single most effective intervention against skin ageing.​

The most effective HA products combine multiple molecular weights, are formulated at appropriate concentrations (0.1 – 2%), and are used as part of a routine that includes sealing moisturisers. Applied correctly, Hyaluronic Acid does exactly what a good hydrator should do: it holds water where the skin needs it most.​

For practical skincare purposes, HA is a strong hydrator, particularly useful in dry climates or when combined with other actives. Expecting more than hydration and modest wrinkle improvement sets up disappointment. Used appropriately, with accurate expectations, Hyaluronic Acid delivers what the research demonstrates it can do. Ultimately, think of Hyaluronic Acid as great for hydration but not a miracle cure.