Glutathione is an antioxidant naturally found in human cells that neutralizes free radicals, boosts the immune system and detoxifies the body. It’s comprised largely of three amino acids: glutamine, glycine, and cysteine. Glutathione levels in the body may be reduced by a number of factors, including poor nutrition, environmental toxins, and stress. Its levels also decline with age. It can also cause skin lightening by converting melanin to a lighter color and deactivating the enzyme tyrosinase, which helps produce the pigment.