Does acupuncture cause scarring on the back?

No. I am not sure if the question is about keloids, which are large pathological scars that form on people who are predisposed to form them. But in general acupuncture does not leave any scars.
Acupuncture. does not cause scarring if done properly. The needles are not put in very deeply. Peace and good health.
No. The diameter of needles is very small and will not cause scarring. Even with gua sha (korean scraping) and cupping the bruising will resolved and should not lead to scars. There is a specific procedure called "scarring moxibustion" which can cause a scar. I don't use it my practice.
No. Acupuncture in trained hands does not cause scarring. The needles used are thinner than hair. Usually there's not even bleeding after the acupuncture needles are removed.