| Summary: | Glutathione (GSH) is present in almost all human cells and has a beneficial effect on human skin brightness. Cysteinylglycine (Cys-Gly) and γ-glutamylcysteine (γ-Glu-Cys) are GSH synthesis components. In this study, we defined glutathione (GSH), cysteinylglycine (Cys-Gly), and γ-glutamylcysteine (γ-Glu-Cys) as cysteine peptide and performed a randomized, double-blind, placebo-controlled study to investigate the effects of orally administered cysteine peptide on human skin brightness using a CM-26d portable spectrophotometer in healthy males and females aged between 20 and 65 years old. Eligible participants were randomly allocated into three groups (cysteine peptide 45 mg: <i>n</i> = 16, 90 mg: <i>n</i> = 15, and placebo: <i>n</i> = 16). Each subject ingested six tablets every day for 12 weeks, and skin brightness was measured at 0, 4, 8, and 12 weeks. As a result, the 45 mg group exhibited arm brightening in a time-dependent manner, and a significant difference was observed compared to the placebo at week 12 (<i>p</i> = 0.028). Moreover, no serious adverse events and changes related to 270 mg study food were observed in the safety trial. Here, we suggest that cysteine peptide is a promising and safe compound for human skin brightness.
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