Sodium Hyaluronate & Molecular Weight: High- vs. Low-Molecular-Weight Hyaluronan

On the INCI list, the internationally standardized nomenclature for cosmetic ingredients, hyaluronic acid almost never appears under that name, but rather as sodium hyaluronate, the sodium salt of hyaluronic acid. The reason: pure hyaluronic acid is poorly water-soluble. Its sodium salt, hyaluronate, on the other hand, dissolves very well in water and is therefore much easier to incorporate into creams, serums, and other cosmetic products.

In terms of their effect on the skin, hyaluronic acid and sodium hyaluronate barely differ, which is why both terms are often used synonymously in practice. More important than the question "acid or salt?" is almost always the question of molecular size.

Hyaluronic acid is a chain molecule consisting of many repeating sugar units. The more of these units are linked together, the longer the chain, and the higher the molecular weight.

This weight is measured in Daltons (Da) or kilodaltons (kDa, 1,000 Daltons).

Why this is important: The chain length is a decisive factor in whether a hyaluronic molecule can penetrate the skin or remains on the surface. And, consequently, how and where exactly it works. That is precisely why it is worth looking at the common terms regarding chain length in context.

In cosmetics, a rough classification into three areas has become established. The exact limit values are not drawn entirely consistently in technical literature, but the following classification is a common guideline:

• Oligo / short-chain: under approx. 10 kDa
• Low molecular weight: approx. 10-1,500 kDa
• High molecular weight / long-chain: over approx. 1,500 kDa

"Short-chain" and "oligo" therefore mean the same thing: the smallest hyaluronic fragments. "Long-chain" is in turn another word for high molecular weight. Between these two poles lies low molecular weight hyaluronic acid, which often plays the main role in serums because it is fine enough to penetrate the skin, but long enough to bind moisture there.

The large molecules are too big to penetrate the skin. They remain on the skin's surface, where they form a fine, moisture-binding film and provide a visible smoothing effect.

Smaller molecules can penetrate the top layers of the skin. There, they replenish moisture reservoirs from within and support the skin's structure over the long term.

In practice, the two variants are not mutually exclusive. Many products intentionally combine multiple molecular sizes to achieve both an immediate and a deep-acting effect. For example, the hyaluronic acid in our Pure Hyaluronic Intense Serum is deliberately chosen to be low-molecular for better absorption, while our Hyaluronic Acid Ampoules combine high- and low-molecular hyaluronic acid for an immediate effect and optimal results when used as a treatment.

Acetylated hyaluronic acid is a chemically slightly modified variant: additional acetyl groups are attached to the molecular chain. This slows down the natural enzymatic degradation of the hyaluronic acid on the skin, allowing the moisture film to be maintained for longer than with unmodified hyaluronic acid.

This special form is found primarily in specialized, often higher-priced formulations. For most skin needs, a well-thought-out combination of high- and low-molecular, non-cross-linked hyaluronic acid already provides a very good result.

In our serum guide, we show which molecular size is behind each hyapur® product.

Would you like to learn more about the active ingredient? Also read our hyaluronic acid guide.