“Contains two types of Hyaluronic Acid!”
You’ve likely seen this marketing claim on countless serum bottles. But as a cosmetic chemist, I often see consumers confused by the terminology. Does a smaller molecule always mean better results? And what is that “Sodium Hyaluronate” listed on the back of your bottle—is it actually the same thing as Hyaluronic Acid?
High vs. Low Molecular Weight Hyaluronic Acid
Hyaluronic acid is widely recognized as one of the most effective hydrating ingredients in skincare. However, not all hyaluronic acid behaves the same way on the skin. Its molecular size—also referred to as molecular weight—directly determines how it functions.
Molecular weight describes the size of a molecule, typically measured in Daltons (Da). In skincare, molecular size is critical because the skin acts as a selective barrier.
As a general rule:
- Only small molecules—typically below ~500 Da—can penetrate the skin effectively
- Larger molecules remain on the surface of the stratum corneum
Hyaluronic Acid by Molecular Size: Why Molecular Size Determines Skin Hydration Depth
High Molecular Weight Hyaluronic Acid (HMW-HA)
High molecular weight hyaluronic acid has a larger molecular size, often exceeding 1,000 kDa. Due to its size, it cannot penetrate the skin barrier.
How it works:
- Remains on the surface of the skin
- Reduces transepidermal water loss (TEWL)
- Immediate hydration and plumping
- Barrier support and soothing effects
In essence, high molecular weight hyaluronic acid acts as a surface humectant, holding onto water at the outermost layer of the skin.
Low Molecular Weight Hyaluronic Acid (LMW-HA)
Low molecular weight hyaluronic acid, often called “mini” or “oligo” HA, is produced by breaking down high molecular weight HA into smaller fragments through enzymatic or chemical processes. Its molecular weight is less than 10 kDa.
Because these molecules are significantly smaller, they are better able to penetrate into the upper layers of the skin.
How it works:
- Moves beyond the skin surface
- Delivers hydration within deeper epidermal layers
- Longer-lasting hydration
- Enhanced skin elasticity
This deeper penetration is the key advantage of low molecular weight hyaluronic acid, allowing it to hydrate beyond the surface level—something high molecular weight HA cannot do.
Why Size Matters: Surface Hydration vs. Deep Hydration
The primary significance of molecular size lies in where hydration occurs:
- High molecular weight HA
→ Hydrates and protects the skin surface - Low molecular weight HA
→ Hydrates deeper layers of the skin
The Best Approach: Multi-Molecular Hyaluronic Acid
Skincare formulations often combine multiple molecular weights of hyaluronic acid to achieve comprehensive hydration. In the lab, I usually work with multiple molecular weights of hyaluronic acid—around 1.40 MDa, 1.60 MDa (high-molecular-weight HA), and 10 kDa (low-molecular-weight HA). Depending on the formulation, I sometimes combine several types to achieve different functional effects.
Why this works:
- Surface-level moisture retention from larger molecules
- Deeper hydration from smaller molecules
- Both immediate and long-term skin benefits
Sodium Hyaluronate vs. Hyaluronic Acid: What’s the Difference?
Pure Hyaluronic Acid (HA) is acidic. If you use a high concentration, it can drop your formula’s pH, which might turn the thickeners into water. From a formulator’s perspective, sodium hyaluronate is more stable in terms of viscosity. Sodium Hyaluronate is nearly pH-neutral.
In addition, pure hyaluronic acid (HA) has many hydroxyl groups that strongly attract each other. The particles tend to stick together and form clumps called “fish eyes.” These clumps absorb water only on the outside, while the inside stays dry. Sodium hyaluronate is the salt form of HA. Because it carries electrical charges, the molecules naturally repel each other. This repulsion helps them spread out evenly in water, so they hydrate faster and more uniformly, with much less clumping.
Despite these processing limitations, don’t get caught up in whether a label says “Acid” or “Hyaluronate.” In a finished water-based serum, the HA has usually dissociated anyway. Many people also think sodium hyaluronate is always a “smaller” form of hyaluronic acid. That’s only partly true. Chemically, sodium hyaluronate is just hyaluronic acid with a sodium ion attached. The real size of the molecule depends on how it’s processed, not on the name.
In practice, manufacturers often break HA into smaller pieces when making sodium hyaluronate, but you can also have high-molecular-weight sodium hyaluronate that stays on the skin’s surface, just like regular HA.
Chemist’s Final Thoughts
Hyaluronic acid is not a single, uniform ingredient—its molecular size determines its function. High molecular weight hyaluronic acid excels at surface hydration and barrier protection, while low molecular weight hyaluronic acid penetrates deeper to provide long-lasting hydration. The combination ensures your skin stays hydrated at every level.
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