N-acetyl-L-Carnosine (NAC) is a natural imidazole-containing dipeptide that has antioxidant activities in cells, particularly against lipid peroxidation. Formulations containing NAC may prevent or resolve cataracts when added to the eyes of animals, presumably through the conversion of NAC to another antioxidant, carnosine. NAC and related dipeptides, delivered in specific formulations, may also have protective effects for skin. N-Acetyl-L-carnosine is used to treat cataracts and to treat UV-induced immunosuppression. N-Acetyl-L-carnosine is also known as NAC, N-acetyl-β-alanyl-L-histidine, Acetylcarnosine, and (2S)-2-(3-acetamidopropanoylamino)-3-(1H-imidazol-5-yl)propanoic acid.