[slumdev]

> There's probably some low grade physiological stress when you use a mask.

When you inhale, your diaphragm contracts and creates a negative pressure inside your thoracic cavity (relative to the outside atmosphere's 101.3 kPa). This pressure, ordinarily, is proportional to the force with which your diaphragm contracts. Adding a layer of fabric restricts the outside air's ability to flow into your thoracic cavity and equalize the pressure. It's like having a congested nose but being unable to open your mouth to bypass the congestion.

There's also the problem of carbon dioxide buildup within the mask. Your unconscious breathing effort is ordinarily controlled by the partial pressure of carbon dioxide in your blood. Carbon dioxide levels, not oxygen levels, are what make you feel "out of breath". The lungs may hold almost a liter of air, but an ordinary unconscious breath exchanges only a tiny fraction of this. That unconscious breath is so small that a large percentage of it may come from air trapped inside your mask, and your alveoli end up being faced with a much higher percentage of carbon dioxide in the air into which they are trying to exhaust carbon dioxide from your blood.

Problems all around.

[briefcomment]

Downvoting facts is sad.