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, GHK Cu Copper Peptide Injections: Advanced Skin Rejuvenation Molecular crystal structure of the tripeptide GHK Cu. In solution, Download Scientific Diagram Defy GHK Cu (glycyl L histidyl L lysine) is a naturally occurring copper binding peptide found in human plasma. As levels decline with age, so may its support of the biological processes involved in collagen production, skin