Copper peptides (primarily GHK-Cu) and L-Ascorbic Acid Vitamin C do not combine well. Ascorbic acid is a chelating agent — it binds to metal ions, including the copper ion that is central to GHK-Cu's mechanism of action. When both are applied in the same session, the ascorbic acid can strip the copper from the peptide complex, rendering the copper peptide inactive. The fix is simple: Vitamin C in AM, copper peptides in PM.
GHK-Cu (glycine-histidine-lysine copper) is a naturally occurring copper-binding tripeptide found in human plasma. Its biological functions are remarkably broad: it stimulates collagen and elastin synthesis, promotes glycosaminoglycan production, activates antioxidant and anti-inflammatory pathways, promotes wound healing, and has been shown to stimulate hair follicle growth. It is one of the most comprehensively studied and genuinely multi-functional actives in skincare, and it achieves results through mechanisms entirely distinct from retinoids or Vitamin C.
Ascorbic acid's antioxidant mechanism involves electron donation, and as part of this chemistry, it can chelate (bind to and sequester) metal ions in solution. Copper is particularly susceptible. When GHK-Cu encounters free ascorbic acid on skin, the copper-peptide complex can be disrupted: the ascorbic acid binds the copper ion, leaving an inactive peptide fragment. This does not damage the skin — it simply means the copper peptide is wasted.
The same concern applies to AHAs at low pH. Highly acidic environments destabilise copper-amino acid complexes. For this reason, copper peptide products should not be applied directly after a low-pH AHA toner or glycolic acid serum.
AM routine: Vitamin C serum (L-Ascorbic Acid) → moisturiser → SPF. This is Vitamin C's optimal slot regardless of copper peptide considerations.
PM routine: Copper peptide serum → moisturiser (ceramide-rich). Keep this completely separate from any acids. If you use AHAs or BHAs in your PM routine, do so on alternating nights — acid nights and copper peptide nights should not overlap.
If you use stable Vitamin C derivatives: The chelation concern is less acute because derivatives are formulated at higher pH and have weaker chelating activity. Some people use stable-derivative Vitamin C products and copper peptides without issue. The strict separation remains more important for L-Ascorbic Acid products specifically.
Copper peptides and Vitamin C are a clear conflict — not because they harm your skin, but because one deactivates the other. The solution is a straightforward AM/PM separation that happens to align perfectly with each ingredient's optimal time of day anyway. Follow this schedule and you get the full benefit of both: Vitamin C's antioxidant and brightening protection during the day, copper peptides' regenerative and collagen-stimulating work at night.