L-cystine is a nutritional supplement. It is used for breast milk of milk powder. It is a non essential amino acid. It is essential for skin and hair, and can promote the treatment of surgery and trauma. Stimulate hematopoiesis and promote leucopoiesis. It can promote the oxidation and reduction of body cells. It can also be used as an additive for cosmetics. It can promote wound healing, prevent skin allergy and treat eczema.