Cystine is two cysteine molecules linked together. The body uses it to make proteins and glutathione, an important antioxidant. People take L-Cystine to strengthen hair and nails and to support skin health. Many combine it with vitamin B6 and other cofactors.
Supplements come as capsules or powder. Taking them with food helps absorption. High doses may cause kidney stones in those prone to them. Check with a doctor if you take medications or have a health condition.