A potent antioxidant that can even be taken as a food supplement. Glutathione makes a fantastic partner to well-studied skin lightening ingredients like kojic acid. While studies show glutathione is safe for use on skin, not so much is known about how well or how quickly glutathione can lighten skin. For this reason, be sure your choice of lightening skincare uses glutathione accompanied by one of the other skin lightening ingredients on this list.