They don’t wear masks all day long. They wear them for a few hours (in a cold, high oxygen environment, if they’re in the OR) and not every day, but only in surgery or if making the rounds where bacterial contamination might be a problem.
They also do not reuse them. Ever. During a long stint in the ER, they'll often swap them for new after a while.
It is lunancy to wear the same mobile petri dish on your face all day, every day.
Many surgeries last for 6-8 hours.