How High Molecular Weight Hyaluronic Acid Forms A Protective Film on the Skin

High-molecular-weight hyaluronic acid is a widely used moisturizing ingredient in skincare products. Its process of forming a protective film on the skin surface is primarily based on its unique molecular structure and physicochemical properties.

Hyaluronic acid is a linear polysaccharide composed of repeating disaccharide units. When the molecular weight exceeds 1.2 million Daltons, it is called high-molecular-weight hyaluronic acid. These molecules have a large number of hydroxyl and carboxyl groups, enabling them to form hydrogen bonds with water molecules. In skincare formulations, high-molecular-weight hyaluronic acid is usually present in aqueous solution. When applied to the skin, water begins to evaporate, and the concentration of hyaluronic acid molecules gradually increases.

As water decreases, the hyaluronic acid molecular chains begin to interact. They intertwine, forming a three-dimensional network structure. This structure is viscoelastic and can spread evenly on the skin surface. Simultaneously, because hyaluronic acid molecules carry a negative charge, a certain degree of electrostatic repulsion occurs between molecules, which helps maintain the stability of the network structure and prevents excessive aggregation of molecular chains.

The resulting protective film is typically on the micrometer scale. The main function of this film is as a physical barrier. It reduces the unintentional evaporation of moisture from the skin's surface while blocking dust and microorganisms from the environment from directly contacting the skin. Due to the large molecular size of high-molecular-weight hyaluronic acid, this film mainly remains on the stratum corneum of the skin's surface and does not penetrate into the deeper layers.

The moisturizing effect of this protective film is related to the concentration used. Generally, a mass fraction between 0.1% and 1% can form a continuous and uniform film. At too low a concentration, the molecular chains cannot fully cross-link to form a complete network; at too high a concentration, uneven film formation or flaking after drying may occur.

This protective film is temporary and will gradually shed with skin metabolism and cleansing processes. Therefore, to maintain the integrity of the protective film, it is necessary to regularly replenish it with skincare products containing high-molecular-weight hyaluronic acid.