Structural Support Healthy Skin, Hair and Nails With Vitamin B-6 and C Non-GMO A Dietary Supplement Kosher Amino Acids Family Owned Since 1968 GMP Quality Assured L-Cysteine is a non-essential sulfur amino acid, which plays a critical role in methionine, taurine and glutathione metabolism. It is also an important component of hair, nails and the keratin of the skin. L-Cysteine stabilizes protein structure and aids in the formation of collagen, being thereby indispensable to skin, hair and nail health.