Can the body adapt to self injury, so it does not hurt and if so why?

Cutters: Some people, usually those who have been badly abused as kids, discover that self-inflicted injury gives a sense of control and temporary peace from internal conflict; they report that any pain does not bother them. It's a downward self-destructive cycle; if you know a cutter, encourage them to get mental health care; if there's danger to life or limb call 911.

Self-injury: With some abused people, self-cutting & self-burning, etc seem to offer temporary relief from unbearable inner pain. Bleeding & pain may even assure them they're still alive. Many are also dissociated when self-harming. It's important to realize that negative thought patterns ("i'm a loser, " "i'm stupid, etc) can be just as damaging -- yet without external scars. Please get help in either case.