PCA stands for Pyrrolidone Carboxylic Acid and though it might not sound like it, it is a thing that can be found naturally in our skin. In fact, after amino acids, it is the second biggest NMF component of the skin with 12% being PCA of the NMF composition of normal skin. So similar to other NMFs, it's a skin goodie that helps the skin to hold onto water and stay nicely hydrated.
- Lodén, Marie. "Role of topical emollients and moisturizers in the treatment of dry skin barrier disorders." American journal of clinical dermatology 4.11 (2003): 771-788.