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, Synergy of GHKCu and hyaluronic acid on collagen IV upregulation via fibroblast and exvivo skin tests Jiang 2023 Journal of Cosmetic Dermatology Wiley Online Library GHK vs GHK Cu Without Copper, Basic Peptide Neurogan Health