L-Cysteine is a conditionally essential amino acid that serves as a precursor for glutathione, the body's most important antioxidant. It is involved in protein synthesis and plays a crucial role in detoxification processes. Cysteine is important for maintaining healthy skin, hair, and nails, and supports immune function. It also plays a role in the synthesis of taurine and coenzyme A, and helps protect cells from oxidative damage.