"what prevents or cures it?"

I took a dance/exercise class from a nurse once. She used to holler, "If it hurts, quit!"

Is your banjo set up right, or do you have press hard to play it? If so, get it adjusted.

Don't get hypnotized. Switch instruments, take a rest.

See a doctor and get the right anti-inflammatory medicine for you. Could be as simple as an over-the-counter drug, but it needs to be the right one.