It is best supported by academic literature for: Topical vitamin C has been shown to help neutralize oxidative stress from UV and pollution, helping to improve photoaging and hyperpigmentation when used consistently
Aging 55 DiwakarL.RavindranathV
Glutathione comes in several forms intravenous, oral, liposomal and topical each with different absorption, convenience and evidence
Glutathione and immune function
doi: 10.1371/journal.pone.0016191 Volker, Herzig, Wood, David, Newell, Felicity, Chaumeil, Pierre-Alain, Kaas, Quentin, Binford, Greta J., Nicholson, Graham M., Gorse, Dominique and King, Glenn F
Sublingual glutathione bypasses first-pass metabolism but still requires enzymatic breakdown by oral mucosal GGT, and plasma levels remain low