Glutathione (GSH)

Identity a tripeptide (glutamate-cysteine-glycine) that, unlike the signalling peptides elsewhere here, functions as the body's principal intracellular antioxidant and detoxifier — maintaining redox balance, neutralizing free radicals, supporting immune function and phase-II detoxification. It's included because it's sold as a skin-lightening / anti-aging peptide-adjacent supplement (oral, topical, and — controversially — IV). ## Mechanism (as proposed) as the cell's master antioxidant, GSH cycles between reduced (GSH) and oxidized (GSSG) forms to neutralize reactive oxygen species, regenerate other antioxidants (vitamins C/E), and drive detoxification. Its skin-lightening action is separate: glutathione inhibits tyrosinase — the rate-limiting enzyme of melanin synthesis — both directly (binding the enzyme's copper site) and indirectly (via its antioxidant effect on the melanogenic pathway), and it shifts melanocytes from producing dark eumelanin toward lighter pheomelanin. The net effect is reduced pigmentation — if enough active glutathione actually reaches the melanocytes, which is exactly the bioavailability problem that oral use faces and that IV marketing exploits. The mechanism is real; the delivery and the clinical magnitude are the weak links.