IMHO opinion I think it's from using the palm of my hand to beat stuff, but the intense vibrations of impacts a close 2nd. Maybe it has to do with the way my hand is ( genetically) cause I know of no one else personally who has this, tho I've read ( internet) and heard about a lot of people in mechanical/industrial trades who encounter this butBest of luck with everything.
I'm curious - do you think it is more from beating on things with your hand/fist or from the jackhammering effect from holding pneumatic tools?