Further explanation of my super glue recommendation: I have thyroid trouble, plus aging skin that is less flexible. For the past few years I've had increasing cracks in my heels and corners of fingers, especially in dry cold, such as when hunting whitetail in the Canadian Rockies in November. Very painful. Lots of experience here with cracked skin on heels.
I now carry a small tube of super glue in my shaving kit and use it at the first sign of a crack in skin.
Prevention is the best way to go but I forget to sand down thick skin and apply Udderly Smooth etc. and don't like to put any such stuff on anyway-- till I get a crack. Then the priority is to fix the damage and pain with glue and start restorative treatments by sanding it down and softening.
Glue the sides of the crack together if possible, but if not, a glue coating over the raw spot reduces pain greatly and allows easier use of the hand or foot. With a flap of skin, glue it down.
