GHK Cu Peptide Progress: Week 3 Results Insulin like growth factor 1 (IGF 1): a growth hormone Molecular Pathology 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, Therapeutic Peptides in Aesthetic, Metabolic and Endocrine Conditions: Effects, Safety, Clinical Applications, and Future Perspectives Growth hormone axis in chronic kidney disease Pediatric Nephrology Springer Nature Link Pediatric Implications of Normal Insulin GH IGF Axis Physiology Endotext NCBI Bookshelf