This sulfur-containing nonessential amino is abundant in beta-keratin, the main protein in nails, skin, and hair, and helps stimulate collagen production. Collagen protein is a major component of the skin and connective tissue, and helps to maintain elasticity and texture. Cysteine is also required in the production of taurine, a sulfurous antioxidant that influences cardiovascular and skeletal muscle function.
One of the most important roles of cysteine is that it is a component of the antioxidant glutathione, which is used throughout the body to neutralize free radicals and diminish oxidative stress. Glutathione is particularly important in detoxification processes in the liver and is thought to help mitigate hangover symptoms and liver damage from alcohol consumption. In the presence of adequate methionine, cysteine levels should remain stable in the body, but in infants, the elderly, and people dealing with metabolic or malabsorption syndromes, cysteine supplementation may be needed.