Cosmetic-grade vs research-grade GHK-Cu — does it matter for topical use?

I do. Caveats: buy from a supplier that publishes a CoA with HPLC purity, reconstitute in a clean environment (isopropyl wipe everything, gloves, use preserved base), make small batches. The molecule is the molecule — purity is the only variable.

Cosmetic-grade premixed also has the advantage of validated preservatives and stability testing. For face use specifically, 'research-grade in your kitchen' is fine for 2 weeks refrigerated, not fine for 6 months on a bathroom shelf.

Makes sense. Small batches it is.

The cost differential is real — you can make a year of 0.1% serum from a single 100mg research vial for under $30. Just treat it like a compounding exercise and don't be gross.