"What are the possibilities that certain 'substances' which might facilitate the 'capture' of undesirable organisms within the air flow ... gets washed out leaving the nasal cavities (perhaps temporarily) unable to 'filter out' those undesirable things?"
Yeah, like ... what if you find yourself in the same theater audience as Hillary Clinton, eh?! You definitely will want your nasal filters working at 110% efficiency, don'tcha know!
The essential American soul is hard, isolate, stoic, and a killer. It has never yet melted. ~ D.H. Lawrence