GHK-Cu + tretinoin — can I layer these or does the retinoid kill the copper?

The main copper-peptide-killer is low pH (vit C, AHA, BHA) because it protonates the histidine and drops the peptide's copper-binding affinity. Tret at the formulation pH (~5–6) is mostly fine. I do tret, wait 20 minutes, GHK-Cu, moisturizer. No interaction I've noticed.

The anxiety about 'degrading' GHK-Cu with adjacent products is overblown. If your routine isn't full of citric acid and ascorbic acid, you're fine. Tret is not the enemy here.

I alternate — tret Monday Wednesday Friday, GHK-Cu the other nights. Easier than timing them. Skin has been great for 6 months.

Morning GHK-Cu, evening tret is the simplest split and the one I'd start with. Lets you see if either is causing irritation in isolation.

Going with morning GHK, evening tret. Thanks all.

General principle that applies here: when combining two actives with independent mechanisms, the default should be temporal separation (AM/PM split) rather than layering. Easier to isolate irritation, easier to stop one.

Saved. Been wondering this exact question.

@cautious_ox azelaic is pH 4–5 which is borderline. I'd either apply it separately with a real gap (30+ min) or switch GHK-Cu to the opposite time of day.

Does the GHK-Cu still work if I'm using an azelaic acid in the morning? That's low pH.

honestly the "don't combine with acidic actives" thing is way overstated. tret literally works better in slightly acidic formulations and ghk-cu isnt some fragile snowflake peptide that denatures at the drop of a hat. ive layered them directly for months with zero issues. if you're worried about it just wait like 10 minutes between applications but i think people are just being extra cautious because they read one skincare influencer say it.

Real question though, did you actually have a baseline before starting tret where you were measuring skin texture or collagen density or whatever you're trying to improve with the GHK-Cu? Because if you're already years in on tret, adding a peptide and then being like "wow my skin looks great" doesn't really tell you if the peptide is doing anything or if it's just tret. The interaction itself is probably fine, most peptides are pretty stable, but I'd be more worried about not being able to tell what's actually working. If you really want to test it clean just run it one way for a month (tret + ghk layered or whatever), then a month with just tret alone, and actually compare.