So the skin in these areas hardens, but if you let it rest for a few days, these calluses disappear and the skin returns (more or less) to its original softness and flexibility.
However, I've noticed that if the tough skin is torn in such a way that it becomes sort of "skin flap" (i.e. attached to the palm only on one side of the callus), then it remains hard and does not revert to its original softness, until it falls off. Why is that? What makes a flap of skin to toughen irreversibly?