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 (know as sodium pyroglutamate, NaPCA, or sodium pidolate) is a popular humectant in skin and hair care formulas thanks to its physiological hydrating action doubling GAGs 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.