I get the problem when I have my fingers in fix. If I spend a day printing and doing some bleaching and holding prints covered in fix, the next day I am likely to have such dry finger tips that especially my thumb will crack. The cure is to put some vitamin E oil on your fingers and then wear surgical gloves all day. The prevention is to put the surgical gloves on before getting your hands in the chems. I get the blue kind that fit very tight and cause very little loss of dexterity.
Also I do get that numb feeling as well.