From the manufacturer
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. Cysteine stabilizes protein structure and aids in the formation of collagen, being thereby indispensable to skin, hair, and nail health.* Natural color variation may occur in this product.