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, Frontiers Exploring the beneficial effects of GHK Cu on an experimental model of colitis and the underlying mechanisms GHK Cu vs NAD+: Which Longevity Peptide Should You Take or Stack? 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 vs AHK Cu: Which Copper Peptide Is More Effective?