Glutamic Acid
Glutamic acid is a small, non-essential amino acid (CAS 56-86-0) that the body can synthesize on its own and that serves as a neurotransmitter in the nervous system. In cosmetics it functions primarily as a humectant moisturizer and skin-conditioning agent. It exists in two distinct mirror-image forms, L-glutamic acid and D-glutamic acid, which appear to have opposing effects on skin barrier repair. It can also act as a pH adjuster and can be metabolically converted into pyrrolidone carboxylic acid, a component of the skin's natural moisturizing factors.
Glutamic acid attracts and retains moisture in the skin, supporting hydration similarly to other amino acid humectants. It can be processed into pyrrolidone carboxylic acid (a natural moisturizing factor), contributing to skin conditioning. Polyglutamic acid, formed by linking many glutamic acid molecules, is claimed to be an even more potent humectant than hyaluronic acid.
The two isomeric forms (L- and D-glutamic acid) have opposing effects on skin barrier repair: topical L-glutamic acid has been shown to delay repair of damaged skin, while D-glutamic acid speeds it up. Because ingredient lists typically do not specify which form is used, the net effect on barrier repair is uncertain when the ingredient is listed simply as "glutamic acid."
