L-pyrrolidone carboxylic acid, also known as PCA or pyroglutamic acid, is the cyclic lactam of glutamic acid. It is present in nearly all living cells, from bacteria to humans, where it is derived from glutathione (an antioxidant). L-pyrrolidone carboxylic acid is also one component of the Natural Moisturizing Factor (NMF) found within the epidermis. Together with the naturally-occurring lipids in skin, NMF components work to keep the skin’s surface intact, supple, and hydrated.

In skin care products, L-pyrrolidone carboxylic acid primarily functions as a humectant moisturizer. After topical application, humectants have the ability to attract and retain the moisture in the air nearby via absorption, drawing the water vapor into or beneath the surface. L-pyrrolidone carboxylic acid also helps to restore the NMF. This is important since the NMF can become depleted with age and also from routine exposure to sensitizing ingredients, which leads to dry, tight-feeling skin. Overall, L-pyrrolidone carboxylic acid helps the skin to look and feel more smooth, hydrated, and firm.