glutathione uses in body Benefits of Glutathione for Skin Lightening :

Source: The potential of GHK as an anti-aging peptide (2020) Claim 2: Intranasal administration bypasses the blood-brain barrier (BBB) to enhance central nervous system (CNS) delivery

[Google Scholar] 98.Venketaraman V., Millman A., Salman M., Swaminathan S., Goetz M., Lardizabal A., David H., Connell N.D

found that the human plasma copper binding peptide GHK added to cultures of mesenchymal stem cells increased their concentrations of VEGF and basic fibroblast growth factor, and also increased endothelial cell proliferation, migration and tubule formation

The hydrophilic peptide doesn't penetrate skin efficiently on its own