🧬 Part 2: The Science of Hyaluronan — Molecular Chemistry & Biological Structure

🔬 The Molecular Architecture of Hyaluronan

To truly appreciate why Hyaluronic Acid (HA) is so effective in dermo-cosmetics, we need to examine its unique molecular structure.

Unlike many other glycosaminoglycans found in human tissue, Hyaluronan is non-sulfated and consists of repeating disaccharide units: D-glucuronic acid and N-acetyl-D-glucosamine.

   [ D-Glucuronic Acid ] <--- Beta-Linkage ---> [ N-Acetyl-D-Glucosamine ]
                                   |
                      Repeated thousands of times
                                   |
              Linear High-Molecular Weight Hyaluronan Chain

These sugar units join together in long, unbranched chains. In its natural high-molecular-weight form, a single Hyaluronan chain can consist of thousands of repeating units, creating a polymer with an exceptionally high molecular weight (often exceeding 1,000 to 3,000 kilodaltons).

🏗️ The Extracellular Matrix: Skin’s Internal Scaffolding

Within the dermis—the deeper layer of your skin—Hyaluronan forms the primary component of the Extracellular Matrix (ECM).

Think of the ECM as a dense, jelly-like mesh that surrounds skin cells (such as fibroblasts). Within this matrix:

• Collagen Fibres provide structural strength and mechanical resistance.
• Elastin Fibres provide flexibility and recoil capacity.
• Hyaluronan fills the spaces between these fibres, holding water to create a firm, cushioned environment.

When Hyaluronan absorbs water, it creates a viscous gel that supports collagen and elastin networks. This hydration cushion maintains skin density, prevents the mechanical collapsing of dermal layers, and keeps the skin barrier plump and resilient.

🌊 Viscoelasticity: How HA Absorbs Stress and Shock

Hyaluronan possesses remarkable viscoelastic properties. This means it can behave both like a viscous fluid and an elastic solid depending on the physical force applied to it:

1. Under Slow Pressure: It flows smoothly, acting as a lubricant between tissue layers and skin cells.
2. Under Rapid Impact: It becomes elastic, acting as a shock absorber to protect cellular structures from mechanical damage.

In facial skin, this viscoelasticity allows your skin to stretch during daily facial expressions—like smiling, frowning, or blinking—and return smoothly to its original position without leaving permanent creases.

🔄 Daily Turnover: The Biological Balance

Hyaluronan is not a static substance. In human skin, it undergoes rapid enzymatic degradation and synthesis:

• High Turnover Rate: Approximately 30% to 50% of the body’s total HA is broken down and replaced every 24 hours.
• Synthesised by Enzymes: Specialized transmembrane enzymes called Hyaluronan Synthases (HAS1, HAS2, HAS3) continually build fresh HA chains directly outside the cell membrane.
• Degraded by Hyaluronidases: Natural enzymes called hyaluronidases break down aged or degraded HA molecules into smaller fragments for recycling.

As long as synthesis equals degradation, your skin maintains optimal moisture, thickness, and elasticity. However, when environmental stress or chronological ageing shifts this balance toward faster degradation, visible signs of skin ageing begin to appear.