Polyglutamic acid, a beneficial ingredient for hydrated skin.

The polyglutamic acid is a biopolymer derived from the polymerization of glutamic acid. It is the main component of nattō, a Japanese dish made with fermented soybeans. Traditionally, the polyglutamic acid was used in medicine to accelerate the healing of wounds and burns. Today, it is primarily recognized for its nutritional contributions but also has several interesting cosmetic properties, starting with its hydrating potential.

The moisturizing properties of polyglutamic acid have been widely demonstrated, including in a clinical study, that is, conducted with human volunteers. This study was carried out with five panelists initially placed for fifteen minutes in a room with controlled temperature and humidity (temperature = 71.6°F and humidity = 60%). Two formulations were then applied to each of their arms: one of them contained 0.2% polyglutamic acid and the other contained 5% glycerol, a moisturizer often used in skincare. Hydration before and two hours after was measured by corneometry. The results are presented in the table below and show the moisturizing effects of polyglutamic acid, superior to those of glycerol.

The polyglutamic acid is a biopolymer that combats skin dehydration at various levels:

• Polyglutamic acid is a film-forming agent.

  Polyglutamic acid has the ability to form a very thin film on the surface of the epidermal tissue. This molecular arrangement is referred to as a microgel. This microgel swells upon contact with water and traps H2O molecules. Thus, not only does polyglutamic acid limit transepidermal water loss, but it also promotes its retention through a humectant process. Indeed, polyglutamic acid can retain up to 5,000 times its weight in water. In comparison, hyaluronic acid can retain up to 1,000 times its weight in water.

• Polyglutamic acid stimulates the production of substances that make up the natural moisturizing factor (NMF).

  The natural moisturizing factor is a set of hygroscopic molecules (amino acids, urea...) that form during the process of epidermal differentiation and retain water in the skin's superficial layer. Studies have shown that polyglutamic acid can boost the production of some of these molecules, including pyrrolidone carboxylic acid (PCA), lactic acid, and urocanic acid. By doing so, polyglutamic acid increases the water content of the stratum corneum, contributing to achieving a more hydrated and softer skin.

• Polyglutamic acid restricts the activity of hyaluronidase.

  Hyaluronidase is the enzyme responsible for the breakdown of hyaluronic acid. As a reminder, hyaluronic acid is a molecule predominantly produced by the dermal fibroblasts that gives the skin its plump and filled-out appearance. The hyaluronic acid acts like a molecular sponge, capturing water. However, over the years, its content decreases: by age 50, the hyaluronic acid reserve has halved. This drastic drop impacts skin hydration and is partly responsible for the appearance of wrinkles and fine lines on its surface. By inhibiting the activity of the hyaluronidase enzyme, polyglutamic acid therefore prevents skin dehydration and the emergence of age-related signs.

Note: While polyglutamic acid aids in maximizing the skin's hydration, its high molecular weight prevents it from acting deeply. Its action is limited to the skin's superficial layers. For complete hydration, it may be wise to pair it with low molecular weight hyaluronic acid, an active ingredient capable of penetrating deeper into the skin.