Under the influence of various opioids, I have scratched my skin raw and still not been able to stop. I feel like most opioids have this effect, but morphine and heroin are the biggest culprits in producing the itch.
For me, it would always be my nose. I would rub the tip of my nose to scratch the itch, probably hundreds or thousands of times in a day. Just a little scratch here and there, but it would add up and when I was no longer high and my sensitivity to pain returned, I would be blown away by how raw I had scratched myself without knowing.
Disinfect with alcohol if the skin has been broken, that's just standard operating procedure. Also, apply a bandage to the effected area.