GHK-Cu (glycyl-L-histidyl-L-lysine copper complex) is a naturally occurring tripeptide found in human plasma, saliva, and urine that binds copper(II) with high affinity. It is one of the most thoroughly researched peptides in skin biology and wound healing, with documented effects on collagen and elastin synthesis, antioxidant enzyme upregulation, anti-inflammatory signaling, and angiogenesis. Research has shown GHK-Cu can reset gene expression in aged tissue toward a younger profile, with studies identifying modulation of over 4,000 genes. It is studied across both aesthetic and repair research contexts for its broad regenerative activity.