They have different abnormalities in making and restoring the active form of glutathione [25, 26, 27, 1]
Garca-Montero C, Ortega MA, Alvarez-Mon MA, Fraile-Martinez O, Romero-Bazn A, Lahera G, et al
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As the clinical report states directly: Glutathione "inhibits melanin synthesis by targeting the enzyme tyrosinase and shifts melanin production from darker eumelanin to lighter pheomelanin, contributing to a more radiant complexion." So Glutathione does two things at once