a dermatoligist, just ask them to try to cauterize part of the affected area and see if theres any results. Its a small laser that looks like a tooth brush with out the end. They just burn it off and it grows back healthy.
the nitrogen just blisters the lip and it grows back without hitting underneath the skin, it only penetrates the puter area. The laser burns off the outer layer as well as the immediate layer underneath killing the affected akin cells thats are part of the problem.