L-cysteine is an optically active form of cysteine having L-configuration. It has a role as a flour treatment agent, a human metabolite and an EC 4.3. 1.3 (histidine ammonia-lyase) inhibitor. It is a serine family amino acid, a proteinogenic amino acid, a cysteine and a L-alpha-amino acid.

A form of cysteine called L-cysteine may help treat arthritis and hardening of the arteries. It may help treat certain lung diseases. These include bronchitis, emphysema, and tuberculosis. Cysteine may play a role in the normal growth rate of hair.

L-Cysteine – an amino acid used to prolong shelf-life in products such as commercial bread – can be found in duck and chicken feathers and cow horns, but most that's used in food comes from human hair.

Cysteine is a non-essential sulfur-containing amino acid in humans, related to cystine, Cysteine is important for protein synthesis, detoxification, and diverse metabolic functions.

L CYSTEINE FOR BIOCHEMISTRY