Usage patterns
〈場所〉にできものができるfor a growth/boil/pimple to form (on a part of the body)
A boil formed on my back.
できものを潰すto pop/squeeze a pimple or boil
If you pop a pimple, it tends to leave a scar.
できものが治るfor a skin growth/boil to heal
After I applied the medicine, the boil healed quickly.