evidence: MYTH: Face masks can reduce oxygen getting to the lungs and bloodstream [...] Some masks mean you have to put more effort into breathing if you wear them for a long time. The N95 mask forms a seal and filters 95 percent of particles. If worn for many hours without a break, an N95 mask might potentially affect oxygen levels but likely not to a dangerous extent, especially in people who are healthy. Looser surgical masks and cloth masks do not lower oxygen levels. It’s important to wear the right mask for the right situation. [...] Remember, if you are healthy and breathing normally, a mask will not lower your blood oxygen levels.