Hyaluronic acid – particularly the salt it forms with sodium – is a popular agent against wrinkles and other concomitant effects of the aging process, and sometimes the most frequently used. The substance is produced naturally by the body, which makes it a very tolerable Active. For example, it is mainly responsible for ensuring that the vitreous body of the eye, with its high water content, remains stable in the eye and can function, boosting its specific qualities and enabling us to see. However, it is also present in the skin. Young skin contains particularly high quantities of hyaluronic acid. With age, the content decreases, and the skin seems less firm and elastic. Fine lines start forming from the age of 25 onwards, followed later by wrinkles and furrows.
Hyaluronic acid achieves its cushioning effect on the skin through its ability to absorb vast quantities of water. This ability is closely linked to its molecular structure: hyaluronic acid is a linear polysaccharide, consisting of D-glucuronic acid and N-acetyl-D-glucosamine units. The very high density of OH groups in the molecule is critical for its functioning. These groups can absorb tremendous amounts of water via hydrogen bonds: roughly 6 g of hyaluronic acid can absorb one litre of water. Generally speaking, therefore, its ability to absorb tremendous amounts of water, plus its good tolerability, are the two reasons why hyaluronic acid is frequently used in cosmetics to slow down the side-effects of the aging process.
Mode of action of hyaluronic acid
The way hyaluronic acid works differs according to its molecular mass – in other words, according to size and weight. More densely interlinked units and, therefore, larger molecules (>2000 kDa) are found alongside medium-sized molecules (approx. 1500–1800 kDa) and small ones (<50 kDa). Because of their different sizes, these natural macromolecules penetrate the skin to various depths, transporting moisture deep into the skin on account of the aforementioned OH groups.
These different effects can be illustrated very clearly by looking at the example of a crow’s foot. The smaller molecules penetrate deepest into the skin layer and infiltrate the wrinkle around the eye, attracting water there and forming a kind of cushion under the wrinkle. With an application concentration of 0.1 %, the depth of the wrinkle can be reduced by around 11 % after 60 days. Its long-term moisturisation can be increased by roughly 16 %, and its elasticity by approximately 13 %. Types of hyaluronic acid with medium or high molecular weights do not penetrate the deeper skin layers. They remain on the wrinkle, thus creating an effect that is less long-lasting but on the other hand more immediate. So in summary, hyaluronic acid attracts water over the wrinkle, forming a cushion there.
Even though hyaluronic acid with a low molecular weight is the most effective for long-term anti-aging treatment, a combination of hyaluronic acids of varying weights yields the best results in a cosmetic product.
A versatile Active, hyaluronic acid has several other effects besides reducing certain visible side effects of age, including inhibiting inflammations, promoting tissue repair, reducing skin irritations, or treating dry eye syndrome. For these reasons, besides its use in cosmetics, hyaluronic acid is also used in medical products.