Glutathione
The most oversold brightening ingredient in the category. What the evidence supports for topical, oral and intravenous use — which are three very different questions.
What is glutathione?
Glutathione is a tripeptide of cysteine, glutamate and glycine, and the body's principal intracellular antioxidant. Its pigmentation interest comes from a real mechanism: it shifts melanin synthesis from darker eumelanin toward lighter pheomelanin and inhibits tyrosinase indirectly.
Three different questions
Intravenous glutathione for skin lightening is widely marketed and poorly evidenced, and has attracted safety warnings from regulators in several countries. It is not a cosmetic proposition and should not be discussed as one.
Oral glutathione faces a bioavailability problem — it is largely broken down in the gut, and evidence for skin effects is thin.
Topical glutathione is the only version relevant to a cosmetic product, and here the honest position is that the molecule is hydrophilic, unstable and around 307 daltons, so delivery is a genuine challenge, and the clinical evidence for topical glutathione specifically is limited. Some work on oxidised glutathione and on delivery-enhanced forms is more encouraging.
How to present it
As a supporting antioxidant with a plausible pigmentation mechanism and limited topical evidence — not as a lightening agent. Vegalab includes it in the Brightening line alongside tranexamic acid, niacinamide, alpha-arbutin and mandelic acid, all of which have stronger individual evidence. That is a reasonable place for it: contributing to a multi-pathway formula rather than carrying the claim.
What does glutathione not do?
It does not lighten overall skin tone in any way supported by good topical evidence, and any product implying it does is overreaching. It is also unstable in aqueous formulation, so stability data matters.