GHK Cu is a naturally occurring tripeptide in human plasma. Levels average 200 ng ml at age 20 and drop to 80 ng ml by age 60 (Pickart et al., 2020). That decline tracks with Does GHK Cu Really Work? 40 Years of Research Reviewed By age 30, your skin produces about 25% less collagen. By 40, that number can reach 40%. This decline affects more than just how your skin looks. It changes how it heals, The potential of GHK as an anti aging peptide