2-pyrrolidone-5-carboxylic acid

Oxidized proline, also known as L-pyroglutamic acid, is insoluble in ether, slightly soluble in ethyl acetate, soluble in water, ethanol, acetone and glacial acetic acid. Its sodium salt can be used as a moisturizing agent in cosmetics. Its moisturizing effect is superior to glycerin and sorbitol. It is non-toxic and non irritating, and is used in skin and hair care cosmetics.