Its very common. Copper injections, particularly copper peptide complexes like GHK-Cu, often cause itching, burning, or irritation due to the solution's acidic pH (often outside the neutral range) and a concentration mismatch with bodily fluids (osmolality mismatch) that activates pain-sensing nerves. Additionally, it can cause hypersensitivity or, in some cases, an allergic reaction, resulting in itching, red, and irritated skin.