The Hostynek and Maibach group at UCSF measured exactly this in 2011: human skin permeation of GHK-Cu as a function of skin layer, with the result that the peptide accumulates in the upper stratum corneum but does not pass through to viable epidermis or dermis in any meaningful quantity 4
In fact, there are numerous cases of people receiving substandard care in the form of the amount of testosterone prescribed and the frequency of their dosage
Pro Tip: For maximum brightening, pair Glutathione with Vitamin C Serum they recycle each other for amplified antioxidant power
In vitro effects of glutamate and N-methyl-D-aspartate receptor (NMDAR) antagonism on human tendon derived cells
The product quality appears premium and easy to use
(2) Another randomised, double-blind, placebo-controlled, parallel, three-arm study conducted with 60 volunteers showed glutathione effectively influenced skin properties such as reducing skin pigmentation and improving elasticity (3)