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Online videos falsely claim that face masks can cause CO2 poisoning

To wear a mask or not to, that is the question that has been fiercely debated online since the start of the Covid-19 pandemic. One of the claims made by opponents of the protective face coverings is that masks can lead to suffocation from the carbon dioxide (CO2) we exhale. Proponents of this theory have posted videos online in which they use gas detectors to claim that the amount of CO2 we breathe when wearing a mask is extremely dangerous. However, there is no factual basis for that claim. We take a closer look.

In a flurry of videos posted online, social media users – most of them American – explain that wearing a mask can be dangerous for your health. To demonstrate this, they use a gas detector, which can be bought in a hardware store for somewhere between 40 and 100 euros, to “measure” the CO2 level inside their masks.

In the videos, the meter goes wild when they start to breathe, indicating a high level of carbon dioxide in the space between their faces and their masks. They claim that this shows you can get carbon dioxide poisoning if you wear a mask and, thus, that you need to avoid wearing one at all costs.

The Dave Sims YouTube channel often shares conspiracy theories about masks as well as anti-vaccine propaganda.

“These machines are used for measuring CO2 in a large space, not behind a mask”


I contacted MSA, the company that manufactures the “ALTAIR 5X Gas Detector”, which is the machine used in some of these anti-mask videos. We asked a representative from the company if this machine can actually measure the level of CO2 in a mask. They responded without hesitation:

This machine is a portable gas detector that should be used to evaluate if the air is dangerous or combustible in a room or a confined space – so we are talking about much larger areas than the interior of a mask.

When you place the machine behind your mask, then the person wearing it will breathe out and displace the oxygen. This sets off the alarm. The same thing would happen if a person breathed out directly into the tube.

Because of the sensitivity of the sensors, combined with the lack of space behind the mask, there isn’t enough time for the meter to drop back down to zero before the next breath, which means the alarm just continues going off.

Because of this, these machines aren’t suited for any kind of medical test and the warnings and alarm on the screen don’t indicate anything important.

This video was posted by Del Matthew Bigtree, one of the most well-known anti-vaccine figures in the United States.

Doctors launch a counter-attack with their own video demos


A number of doctors and nurses made their own science-based videos in response to the flood of videos claiming that wearing a mask could lead to CO2 poisoning. In some of the videos, they put on a mask – or even several masks – and measured the level of oxygen in their blood. They demonstrated that wearing one, or even several masks, doesn’t reduce the level of oxygen in your blood.

However, several scientific studies conducted years before masks had become such a polarising issue did suggest that wearing a mask could provoke minor changes in the level of oxygen in the human body.

For example, a study carried out by the University of Başkent in Turkey in 2008 measured the blood oxygen levels of surgeons to see if they could be affected by the masks they wear when carrying out operations. The study showed that wearing a mask for an hour led to a small decrease in the level of oxygen in a person’s blood and a mild increase in their heart rate.

“The level of CO2 increases when you wear a mask, but it remains a reasonable level for the human body”

I discussed these studies with Ewa Messaoudi, who handles the regulation of protective respiratory devices at AFNOR, the French organization that implements product standards:

It’s important to take into account that this kind of protection is always a constraint for the human body. We don’t wear a mask for respiratory comfort, we wear it to protect ourselves against an existing risk. What’s important to establish is if the mask allows the human body to meet its physiological needs for the limited period when it is being used.

When we develop masks, we model them on technical specifications based on human factors, like European norms of standardization.

So, yes, the level of CO2 does go up when you wear a mask but it remains an acceptable level for the human body. That’s the case for masks certified by the CWA 17553 [Editor’s note: the Committee Workshop Agreement of the European Normalization Committee, which provides information about these masks on this document].

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