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Masks Result in Breathing CO2 Levels Five Times More Than the Legal Workplace Limit

Wearing a mask significantly increases CO2 concentration we breathe and significantly decreases oxygen concentrations we breathe, and probably even increases blood CO2 and decreases blood oxygen levels, despite our bodies’ excellent systems for maintaining those. The CO2 concentration you are breathing when wearing a mask is more than five times the U.S. OSHA legal limit for CO2 concentration in the air workers are supposed to be exposed to. But instead of enforcing that legal safety limit, the U.S. and state and local governments are ordering businesses to violate it. (The good news is its only twice the legal limit for children!)

Wrap your head around that: schools and government are ordering students, workers, and the adult public to be exposed for hours on end to levels of CO2 that the government has already determined to be dangerous and hazardous to us.

Rhee et al. (1) measured CO2 levels wearing an N95 mask, a valved respirator, and a powered respirator. The powered respirator is powered by batteries to electrically pump air in and out through a filter. The N95 is the only one of these commonly used. It is the best for filtering viruses as well as bacteria or smoke or particulates in air. It is widespread in health care settings. Gas levels were measured at the outlet of the nostrils.

Wearing an N95 at rest results in breathing CO2 concentrations of 2.6%, compared to 0.26% with no mask. So wearing an N95 increased the CO2 concentration a wearer breathes by 10-fold. The change is immediate. The 8-hour U.S. National Institute of Occupational Health (NIOSH) limit is 0.5% and the 15-minute exposure limit is 3.0%. So wearing an N95 immediately results in breathing concentrations of CO2 that are 5 times higher than the 8-hour legal limit and just barely below the 15-minute legal limit in the U.S. The valved respirator gave essentially the same result at 2.4% CO2. The battery-powered respirator (have you ever even seen anyone wearing one of those?) did better, but it still resulted in a CO2 concentration of 0.56%, which is more than double the concentration without a mask and slightly above the 8-hour legal limit of 0.5%.

Rhee et al. did not study the much more common surgical masks or cloth masks, but they would be much closer to the N95s than to the battery-powered respirator.

It is interesting to see the Rhee et al. authors struggle to say that their results are no big deal and nothing anyone should be concerned about. Even though every worker forced to wear a mask is wearing one for closer to 8 hours than to 15 minutes and the the masks result in CO2 concentrations vastly in excess of the legal 8-hour limit, the authors hasten to add that the CO2 levels “were “below the 15-min short-term exposure limit” [barely]. And they write that since the battery-powered respirators (which virtually no one uses) gave results only slightly above the 8-hour exposure limit, “there should not be a concern in their regular day-to-day use for health care providers.”

Similarly, Wallach et al. (2) reported inhaled air CO2 concentration of 1.312% in children wearing a surgical mask and 1.391% wearing an N95. The Wallach et al. paper (2), I should note has been retracted by the journal. But I have corresponded with the author and there seems to have been no reason to retract the study other than that the journal found it politically inconvenient. And the Wallach results are entirely consistent with the results of Rhee and the other papers I will discuss.

The results of those two studies are shown in the table below.

Similarly, Driver et al. (3) found wearing a cloth mask during treadmill exercise resulted in significantly increased pulse rate, decreased maximal oxygen consumption, and increased labored breathing.

Roberge et al. (4) found wearing a surgical mask during treadmill exercise resulted in significantly increased heart rate, breaths per minute, and blood CO2 concentration.

Tornero-Aguilera et al. (5) found that university students wearing surgical masks had increased mental fatigue and slower reaction time compared to no mask. And they had a higher heart rate (89 vs. 77), and lower blood oxygen saturation (96.0% vs. 98.4%).

Does any of this matter?

Of course it does! The U.S. and German governments thought it mattered when they established safety limits for the CO2 concentrations we should be exposed to. And those limits are vastly exceeded when you wear a mask.

Of course people don’t die, at least not immediately, when they wear a mask. But I would have little doubt that wearing a mask for 6 hours a day or 8 hours a day, as many students and workers are forced to do, significantly increases the likelihood you will become depressed, abuse drugs, abuse alcohol, die of drug or alcohol overdose, and probably increases the likelihood you will die by suicide. Short term, the decreased oxygen and increased CO2 you experience when wearing a mask decreases your IQ and mental acuity and mood.* That is why outdoor air feels good: it has more oxygen and less CO2 than indoor air. And mask wearing makes a much bigger difference than being indoors versus outdoors.

*I am not going to bother to look for scientific literature that finds that oxygen and CO2 concentration have effects on mood, mental acuity, and IQ. I think we all intuitively know that. I have seen articles in the media that reported on scientific studies with those conclusions, including an article I recall that reported that people score measurably lower on IQ tests with stagnant indoor air than with windows open or with plants indoors (plants emit oxygen and consume CO2).


1. Rhee MSM, et al.. Carbon dioxide increases with face masks but remains below short-term NIOSH limits. BMC Infect Dis. 2021 Apr 16;21(1):354. PMID: 33858372; PMCID: PMC8049746.

2. Walach H, Weikl R, Prentice J, Diemer A, Traindl H, Kappes A, Hockertz S. Experimental Assessment of Carbon Dioxide Content in Inhaled Air With or Without Face Masks in Healthy Children: A Randomized Clinical Trial. JAMA Pediatr. 2021 Jun 30:e212659. PMC8246331.

3. Driver S. et al. Effects of wearing a cloth face mask on performance, physiological and perceptual responses during a graded treadmill running exercise test. Br J Sports Med. 2022 Jan;56(2):107-113. Epub 2021 Apr 13. PMID: 33849908; PMCID: PMC8050876.

4. Roberge RJ, Kim JH, Benson SM. Absence of consequential changes in physiological, thermal and subjective responses from wearing a surgical mask. Respir Physiol Neurobiol. 2012 Apr 15;181(1):29-35. Epub 2012 Feb 2. PMID: 22326638.

5. Tornero-Aguilera JF, Clemente-Suárez VJ. Cognitive and psychophysiological impact of surgical mask use during university lessons. Physiol Behav. 2021 May 15;234:113342. Epub 2021 Jan 29. PMID: 33516744; PMCID: PMC7844352.

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