Even the M95 only stops particles down to about 5 microns. The virus is 250 times smaller. Masks do accumulate bacteria so you can concentrate them and re-breath them. Masks do lower O2 levels which eventually affects the brain. It can be said that long term wearing of masks will starve the brain of O2 and make you more stupid. Maybe that is the goal of the supporters of masks; leads to idiocracy.
and that is if the N95 is fit appropriately and tested. The ones I see people wearing in the grocery store are not