PCA or Pyrrolidone Carboxylic Acid (2-pyrrolidone-5-carboxylic acid) is an amino acid naturally occurring in the skin. It is a metabolite of Filaggrin (one of the pivotal proteins that play a crucial role in skin barrier function). In addition, Pyrrolidone Carboxylic Acid is one of the essential NMFs (natural moisturizing factors) of the skin.
It's the most hygroscopic amino acid in the epidermis, which means it has the most potent water-binding ability and naturally provides hydration, elasticity, and volume. As a result, PCA and its sodium salt (known as sodium pyroglutamate, NaPCA, or sodium pidolate) is a popular humectant in skin and hair care formulas thanks to its physiological hydrating action doubling GAG moisture retention capability. It also restores disordered lipid structure, improving skin barrier function.
Cold weather negatively affects the natural degradation process of Filaggrin, so people living in northern latitudes or frequently being under A/C cold airflow should consider using skincare products with PCA. It is also essential for dry skin or atopic conditions.
The role of PCA
The well-being of the horny layer depends on the maintenance of an adequate water level in the skin. In normal conditions, the water level in the horny layer is between 20-35%; this quantity of water gives the horny layer the essential characteristics of softness, flexibility, and elasticity.
The horny layer is made up of 30% of moisturizing substances, 12% lipids, and 58% of keratin. The 30% of these moisturizing substances (which go under the name of NMF) are soluble in water and have water bonding properties: their function is to give the horny layer water bonding capacities; PCA forms 12% of NMF.
The lipids of the horny layer come from the lamellar bodies of the epidermis and are composed of a complex mixture of cholesterol, free fatty acids, unsaturated fatty acids, and ceramides. These lipids bond with the protein shell of the corneocytes and have a selective permeability moisturizing role. Because of all of this, it can be seen how both the hydrophilic (NMF) and lipophilic substances are important in maintaining the correct hydration level of the cutis.