Hyaluronic Acid in Skincare: Molecular Weight and What It Changes
Hyaluronic acid is on the front of more products than any other active and is one of the least understood. Nearly all of what is sold is not hyaluronic acid at all but sodium hyaluronate, and the single most important technical variable, the molecular weight, is rarely stated on the pack even though it determines depth of penetration, skin feel, viscosity contribution and how the formula behaves over time.
Why Molecular Weight Is the Whole Story
The molecule is a long chain of repeating disaccharide units. The chain length, expressed as molecular weight in daltons, determines how far it penetrates and how much water it can hold.
- High molecular weight, above roughly 1,000 to 1,500 kilodaltons. Stays on the surface and forms a continuous film. It is what produces the immediate plumping and smoothing sensation, and it is also what produces the tight, tacky after-feel that some consumers dislike. It contributes strongly to viscosity.
- Medium molecular weight, roughly 100 to 1,000 kilodaltons. Partially penetrates the upper layers. A reasonable compromise between feel and penetration, and the most useful single grade for a general purpose serum.
- Low molecular weight, below 100 kilodaltons. Penetrates further into the upper layers of the skin. Contributes almost no viscosity and no surface film, so it must be paired with something that provides body. It is also the grade most often claimed as "penetrating" in marketing.
- Very low molecular weight and oligomers. Below about 10 kilodaltons. High penetration and a growing category, but the evidence base is thinner and the cost is higher.
Why a Blend Outperforms a Single Grade
A serum built on one grade always has a weakness. All high molecular weight gives an excellent immediate feel and no lasting effect. All low molecular weight disappears into a watery liquid that does not feel like a serum at all.
A blend of three grades gives surface hydration from the high fraction, mid layer hydration from the medium, and penetration from the low, while the high fraction supplies the viscosity and the film that makes the product feel substantial. This is why the multi weight claim has become standard, and it is technically justified rather than a marketing invention.
The practical formulation question is the ratio. A typical starting point is roughly equal total content split with a bias toward the medium grade, then adjusted by sensory evaluation. The ratio affects feel far more than it affects measured hydration, so it is a sensory decision supported by instrumental data rather than the reverse.
Use Levels and Cost Reality
Sodium hyaluronate is usually added at 0.1 to 1 per cent, most commonly 0.2 to 0.5 per cent in a serum. The raw material arrives as a powder at high purity and is expensive per kilogram, but at these use levels the cost contribution to a finished unit is modest. The confusing part is the labelling.
Many products state a percentage that refers to a pre-made blend rather than the pure material. A product described as containing 2 per cent hyaluronic acid may contain 2 per cent of a complex that is itself a small percentage of sodium hyaluronate. Ask the supplier for the pure material content and calculate the finished formula figure, because that is what any claim has to be based on.
Formulating With It
Three practical points that come up in nearly every project:
- It is a powder that hydrates slowly. Sodium hyaluronate forms lumps if added quickly to water, in the same way as other hydrocolloids. Pre-dispersing in glycerin or propanediol and then adding the dispersion to water under moderate shear gives a smooth result. Full hydration can take a few hours, so it should go in early in the process, not at the end.
- It contributes viscosity, which is not always wanted. A formula designed around a low molecular weight grade is watery. A formula with high molecular weight at 0.5 per cent is noticeably thick. The choice interacts with the rest of the rheology system, so it is not an independent decision.
- It is a humectant, so it needs an occlusive partner. In a dry environment a humectant film can draw moisture from the skin rather than from the air. Pairing it with an emollient or an occlusive in the same formula avoids the complaint that a hyaluronic serum made skin feel drier after a few hours in winter.
Stability, Preservation and Compatibility
Hyaluronic acid is chemically robust compared with vitamin C or retinol. The chain can be broken by heat and by aggressive shear, which reduces molecular weight and therefore changes both feel and performance. High temperature processing and prolonged high shear homogenisation should be avoided.
Microbiologically, a formula containing hyaluronic acid is a more attractive environment for microbes than plain water because the polymer is a nutrient source. Challenge testing on the actual formula is essential; a preservative system validated in a simple aqueous base may not hold in a hyaluronic formula.
Compatibility with cations matters too. In the presence of certain polyvalent ions the polymer can cross-link and form a gel or a precipitate. That is occasionally used deliberately to create a texture, but it also means the order of addition and the ionic content of the other ingredients have to be checked rather than assumed.
Claims and the Regulatory Position
In the European Union collagen and hyaluronic acid were among the substances affected by the assessment of health claims, and the practical consequence is that no authorised oral or topical claim for a specific physiological effect exists. Claim language should stay in appearance territory: helps skin appear hydrated and plump, smooths the look of fine lines, provides lasting hydration as a cosmetic property.
Substantiation for a hydration claim is usually instrumental. Corneometry readings at defined intervals after application on 20 to 30 volunteers are inexpensive, quick and give a number that supports the wording. A claim of improving the skin barrier is a different and harder claim that needs trans-epidermal water loss measurement over a longer period.
Hydration Formulas Developed With the Right Grade
OEM COSMETICS ODM formulates serums, essences, gels and creams using multi weight sodium hyaluronate systems on ISO 22716 and GMP certified lines, with hydration measurement, stability and challenge testing on the finished formula. Tell us the feel you want and we will propose the grade ratio and the supporting emollient system.
Talk to our team: WhatsApp +86 18709713948 · Email adon@oemcosmeticsodm.com · Website www.oemcosmeticsodm.com