The effects of the oral supplementation of L-Cystine associated with reduced L-Glutathione-GSH on human skin pigmentation: a randomized, double-blinded, benchmark- and placebo-controlled clinical trial

J Cosmet Dermatol. 2022 Feb;21(2):802-813. doi: 10.1111/jocd.14137. Epub 2021 Apr 22.


Background: Glutathione has become a potential skin-lightening ingredient after the discovery of its anti-melanogenic properties. Various mechanisms of action have been considered to explain this property, one of them being the skewing of the melanin synthesis pathway toward the production of lighter pheomelanin instead of darker eumelanin, consequently producing a lightening effect.

Aims: To evaluate the skin lightening and anti-dark spot effects of oral supplementation with L-Cystine associated with L-Glutathione as compared to placebo and benchmark.

Methods: Effects of this L-Cystine-L-Glutathione oral combination were investigated in a 12-week randomized, double-blind, parallel-group, benchmark- and placebo-controlled trial involving 124 Asian female subjects. Women were randomly allocated into 4 equal groups (500 mg L-Cystine and 250 mg L-Glutathione, 250 mg reduced L-Glutathione, 500 mg L-Cystine, or a placebo, daily). Skin color was measured at baseline, after 6 and 12 weeks by spectrophotometry. Size and color of facial dark spots were determined from digital photographs.

Results: A significant skin lightening was observed after 12 weeks of oral supplementation with L-Cystine associated with L-Glutathione. This combination also induced a significant reduction in the size of facial dark spots after 6 and 12 weeks. It is noteworthy that the observed effects were not only significantly better than those obtained with placebo, but also with L-Cystine alone or L-Glutathione alone.

Conclusion: The daily oral administration of 500 mg L-Cystine and 250 mg L-Glutathione during 12 weeks was a safe treatment to effectively lighten the skin and reduce the size of facial dark spots of Asian women.

Keywords: L-Cystine; L-Glutathione; eumelanin; oral supplementation; pheomelanin; skin pigmentation.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Cystine* / therapeutic use
  • Double-Blind Method
  • Female
  • Glutathione* / therapeutic use
  • Humans
  • Skin Pigmentation* / drug effects


  • Cystine
  • Glutathione

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