There are no medical exceptions. That's a made up story by people that don't want to wear the mask.
Saw video of Dr. putting on 6 masks while wearing a pulseox monitor. Needle never moved.
It was no bearing on COPD, Asthma etc. All made up.
Oxygen cells are so much smaller, they fly right through the material.
The mask is to stop much larger organisms, such as cough sputum etc.