evidence: Do masks cause lower oxygen levels? [...] This presents a major problem for two reasons: masks definitively don’t harm oxygen levels and, right now, they’re our best weapon against the spread of COVID-19. Fortunately, the flurry of complaints has also given rise to a number of highly effective demonstrations in which medical professionals display their excellent oxygen levels while trying on different masks—and sometimes multiple masks at once. Believe these demonstrations, because they’re true. Many professions require the regular use of masks, and the people who wear them don’t suffer as a result.