Hyaluronic Acid Explained: Molecular Weights, Skin Penetration and Why Size Matters

Updated: May 2026  ·  Reading time: approx. 8 minutes

What hyaluronic acid is and how it works

Hyaluronic acid (also called hyaluronan or hyaluron) is a polysaccharide - a complex sugar molecule - that occurs naturally throughout the body. It is most concentrated in the skin, where it is the primary water-binding molecule in the extracellular matrix. It also occurs in joints (where it lubricates cartilage), in the eyes (in the vitreous body, where the name originates from the Greek hyalos, meaning "glass"), and in connective tissue throughout the body.

The molecule's defining property is its extraordinary water-binding capacity: a single gram of hyaluronic acid can hold up to six litres of water. In skin, this makes it the critical component for maintaining tissue hydration, volume and suppleness. It holds water within the dermal matrix, creates the gel-like environment that fibroblasts (the cells producing collagen and elastin) need to function optimally, and acts as a buffer against mechanical stress.

Hyaluronic acid is produced naturally by keratinocytes and fibroblasts in the skin. Its concentration declines measurably from the third decade of life, contributing to the progressive reduction in skin elasticity, plumpness and moisture retention that characterises intrinsic skin ageing.

Why molecular weight changes everything

Hyaluronic acid in its natural form has a molecular weight of 4,000 to 8,000,000 Daltons (Da) - an enormous range. In cosmetic formulations, different fractions of this range are used deliberately, because molecular size determines how far the molecule can travel through the skin's layered architecture.

The stratum corneum - the outermost layer of the skin - is a physical filter. Large molecules cannot cross it. Smaller molecules can. This is why molecular weight is not a technical detail: it determines whether a hyaluronic acid molecule stays on the skin surface (useful for immediate plumping and surface moisture retention) or whether it penetrates into the living cell layers below (useful for lasting structural hydration and support of the skin's own repair processes).

The five molecular weight ranges and where each one works

Within the broad range of commercially available hyaluronic acid, five distinct weight categories are relevant for skincare formulation. Each works at a different depth:

The three highlighted rows represent the most clinically validated range for cosmetic use. Ultra-high provides the visible immediate result. Medium and low provide the structural lasting result. Ultra-low is where formulation expertise matters most - it is potentially the most potent but requires precise dosing and is not appropriate for all products or concentrations.

The INCI label problem: what Sodium Hyaluronate does not tell you

All sizes of hyaluronic acid in cosmetic formulations are declared on INCI lists as Sodium Hyaluronate - the salt form of hyaluronic acid, which is more stable in formulations than the free acid. Occasionally you may also see Hyaluronic Acid listed directly. Both names are used for all molecular weight variants.

This is not an accident or a regulatory failure - it reflects how INCI nomenclature works. The system names compounds, not their physical forms. What it means practically is that the quality and depth of hyaluronic acid hydration is entirely at the discretion of the brand. A brand committed to formulation transparency will tell you which molecular weight range it uses, and why. A brand that only lists "Sodium Hyaluronate" without further explanation may be using a single weight, and it is most likely a high molecular weight for cost efficiency and visible immediate effect.

What clinical evidence says about the optimal molecular weight range

A key reference for optimal hyaluronic acid molecular weight in skincare is a study published in the Journal of Dermatological Science (PMC8322246), which identified the most effective range for cutaneous use as 80,000 to 1,000,000 Daltons (80-1,000 kDa). Within this range, hyaluronic acid demonstrates measurable and clinically significant effects on skin hydration, elasticity and fine line reduction, with a favourable safety profile.

The clinical picture outside this range is nuanced:

Above 1,500,000 Daltons: molecules cannot penetrate the stratum corneum and their effect is limited to surface film formation. This produces visible short-term results but is metabolised away rapidly with each cleansing cycle. There is no lasting structural contribution to skin hydration.

Below 10,000 Daltons: ultra-low molecular weight HA has demonstrated pro-inflammatory activity at higher concentrations in in-vitro models. At controlled low concentrations it can support cellular regeneration, but the safety margin is narrower. Products containing ultra-low weight HA benefit from experienced formulation oversight and appropriate concentration limits.

Why multi-molecular formulations outperform single-weight ones

The skin is not a flat surface - it is a layered architecture, and different processes occur at different depths. Trans-epidermal water loss (the passive evaporation of moisture from the skin surface) is primarily a stratum corneum phenomenon, best addressed by surface-active high molecular weight HA. Structural hydration of the dermal matrix and support of fibroblast function is a mid-to-deep epidermal process, best addressed by low and medium molecular weight HA. A single molecular weight can only address one of these simultaneously.

Multi-molecular formulations work across several depths at once:

High molecular weight forms a moisture-retaining surface film, immediately reducing water loss and providing the visible plumping and smoothing effect that makes skin look hydrated after application.

Medium molecular weight penetrates the epidermis and is retained in the connective tissue, providing longer-lasting moisture storage that persists across the cleansing cycle and progressively improves skin texture and fine line appearance with regular use.

Low molecular weight reaches the deepest accessible layers, stimulates fibroblasts to increase their own hyaluronic acid production, and supports the collagen and elastin synthesis environment.

The result of combining these is hydration that is simultaneously visible (surface), sustained (mid-layer), and structurally supportive (deep). No single molecular weight achieves all three.

How to use hyaluronic acid correctly for maximum effect

Hyaluronic acid is a humectant - it attracts and binds water, but it cannot prevent that water from subsequently evaporating. This is the most important practical point for getting lasting results from a hyaluronic acid product.

Apply to slightly damp skin. When skin is damp, hyaluronic acid has immediate water to bind. On completely dry skin in a dry environment, high molecular weight HA can actually draw moisture upward from deeper skin layers rather than from the surface - counterproductive for persistent dryness.

Follow with an occlusive or emollient layer. A face oil, moisturiser or barrier cream applied immediately after a hyaluronic acid serum seals the moisture in. Without this second step, the water that HA has bound will evaporate through the skin surface over time, and the benefit diminishes faster than the ingredient's absorption suggests it should.

Consistency matters more than concentration. Low molecular weight HA's benefit to fibroblast stimulation and connective tissue hydration accumulates with regular use. The visible result of daily application over four to six weeks is more significant than the result of a single application at any concentration.

NAYA's five-molecular-weight complex and Tremella

Five molecular weights in the Cell Resilience Serum

The Cell Resilience Serum uses five molecular weight variants of hyaluronic acid in a single formulation, covering all five weight categories from ultra-high to ultra-low. This provides simultaneous surface moisture retention, mid-layer sustained hydration and deep structural support in a single serum step. All five are vegan (biotechnology-derived rather than animal-sourced).

The molecular weight selection is based on the clinical evidence range. The ultra-low weight fraction is formulated at concentrations designed to stay within the established safety parameters, providing cellular regeneration potential without the inflammatory risk that higher concentrations carry.

Tremella fuciformis: the plant-based complement

The Cell Resilience Serum also contains Tremella fuciformis polysaccharide extract - Silver Ear Mushroom - widely used in Japanese and Chinese skincare for its moisture-retaining properties. Tremella polysaccharides form a film on the skin surface and function as a plant-based surface humectant with a molecular structure that some research suggests allows finer particle sizes than conventional high molecular weight HA, potentially allowing slightly better surface-layer integration. Tremella extract is also a potent antioxidant, protecting against oxidative stress from UV and environmental pollution - addressing a mechanism that HA alone does not cover.

Frequently asked questions

© NAYA Skincare. All information is for educational purposes and does not constitute medical advice.