I have no medical training or education whatsoever (beyond the standard “Get the Science Credits Knocked Out” college Biology class) and I knew this from the get-go. We are not designed to breathe in our own exhaust.
I especially hated seeing masks on little children. If adults want to participate in that nonsense, fine. But let those kids breathe freely.
“We are not designed to breathe in our own exhaust.”
Also, my ophthalmologist HATED the masks. To paraphrase you, we are not designed to exhale cooties living in our masks up in to our eyes.