Cutting off a blister:
It is forbidden to cut a blister from one’s body whether with ones hand [or teeth] whether with a vessel, whether for himself whether for others, whether it is [filled with] puss [blister] whether it is dry. If one does cut a puss [filled] blister with a vessel he is liable for the shearing prohibition according to those which hold one is liable for shearing even if he does not require that which is being sheared.
It is a Biblical prohibition according to some opinions to cut off a blister with a vessel, if the blister is filled with puss. It is Rabbinically forbidden to remove it with one’s hands [or teeth] even if it is dry.