Pyroglutamic acid (also known as PCA, 5-oxoproline, pidolic acid) is a ubiquitous but little studied natural amino acid derivative in which the free amino group of glutamic acid or glutamine cyclizes to form a lactam. The names of pyroglutamic acid conjugate base, anion, salts, and esters are pyroglutamate, 5-oxoprolinate, or pidolate.

The sodium salt of pyroglutamic acid is used for dry skin and hair products, as it is a humectant. It has low toxicity and is not a skin irritant.

Pyrrolidone carboxylic acid (PCA) is obtained by thermal cyclisation of l-glutamic acid (dehydration reaction) derived from sugar beet molasses.