From a medical perspective.
For the last year and a half, dedicated mask werers have been wearing their masks as much as humanly possible, in all kinds of weather conditions. They have been breathing in their own carbon dioxide for hours at a time. At the same time they are decreasing their oxygen intake to some small degree.
This couldn't have been healthy for the brain. We have heard of short term effects like headaches and blurry vision, but what is the cumulative long term effect?
Is there some kind of brain damage taking place?
Are the mental faculties being affected?
Mask wearers are definitely being changed? The question is into what?