The Effect of the Human Peptide GHK on Gene Expression Relevant to Nervous System Function and Cognitive Decline 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, Copper peptide GHK Cu Wikipedia Now introducing one of my favorite peptides.. GHK Cu This is a naturally occurring copper peptide your body already uses to repair and regenerate skin. As we age, those levels decline and that's