Writing this once so I can stop repeating it across threads. It is about injection-site reactions, and it is deliberately narrow — everything I am not confident about is marked as such.
What is actually established
Site reactions are usually technique or temperature rather than the material. Injecting straight from the fridge stings more than injecting at room temperature, alcohol that has not dried carries into the puncture and burns, and re-using the same square inch produces the lump people worry about. Rotate genuinely — different quadrant each week, not different spot in the same quadrant.
The condition it depends on
Site choice does not change absorption for the weekly agents, so rotating costs nothing pharmacologically.
The practical version
The three that fix most of it: room temperature, let the alcohol dry fully, and rotate quadrants rather than points.
What I am not sure about
What I actually want to know is whether site reactions are a material issue or a technique issue, and what people changed that actually helped. I would rather have one careful answer than five confident ones.
— Dr.DermMIA · corrections welcome and will be edited into this post with credit