https://jamanetwork.com/journals/jama/fullarticle/2764955
Quote:
> Oxygen concentration inhaled by healthy subjects wearing a surgical mask covering an N95 respirator decreases to about 17%, and the concentration of carbon dioxide increases to about 1.2% - 3% in a short period of light work (2-3). Although participants did not show any obvious changes in physical function and did not have any discomfort ratings, the average carbon dioxide concentration inhaled was far higher than the limit of 0.1% of indoor carbon dioxide concentration in many countries. With prolonged mask wearing, untoward reactions may gradually appear. In another long-term study, after wearing an N95 mask for 12 hours the CO2 concentration of subjects increased to 41.0 mmHg, far higher than the baseline value of 32.4mm Hg at the beginning of the test (4). The subjects mainly reported headache, dizziness, feeling tired and communication obstacles. In real life, the situations and time of wearing masks are much longer than the above experimental research settings.