@Kelly Algiere it is a histamine response, meaning because the peptide—or the free copper ions it releases—acts as a localized irritant that activates mast cells, causing them to release histamine, resulting in itching, redness, or swelling. This is often a sign of mast cell activation rather than a true allergy, particularly common with injections. For me I made the choice to keep going and my sting reduced after 7-9 days and now being on week 5 I don't have reaction.