Cysteine The amino acids that the body cannot produce, and need to be taken in through the diet, are called essential. Cysteine and cystine are two of these amino acids. Cystine simply contains two molecules of Cysteine bonded together, which increases stability. Cysteine plays an important role in the formation of keratin and collagen, and the detoxification processes in the liver. Keratin gives strength to the fingernails, toenails, skin and hair. Visit - https://www.nationalnutrition.ca/articles/supplements/cysteine/