Fact Check-COVID-19 face masks do not trap dangerous levels of carbon dioxide

A video of a woman breathing directly onto a carbon dioxide monitor while wearing a COVID-19 mask has been used to support the false claim that face coverings trap dangerous levels of carbon dioxide (CO2).

The clip, (here) which has been shared 6,500 times on Facebook, shows the woman criticizing the recommendation for some children in Ireland to wear face coverings (here).

Putting what she calls a “professional carbon dioxide detector” into her mask, she says an alarm will sound “when it reaches dangerous levels” and that a reading of over 5,000ppm of carbon dioxide can lead to headaches, drowsiness, anoxia, cerebral injury, coma and even death.

The device starts beeping after being placed in the mask for approximately twenty seconds and presents a reading of 1,895, before rising to 10,000. “This is dangerous,” the woman says.

Experts told Reuters that the device would show the same result without a mask, and that breathable masks cannot trap CO2 to a dangerous level.

“Of course, if you are breathing directly into a CO2 meter, with or without a mask, the concentration will be high, because the gas is in your exhaled? breath,” Lidia Morawska, Distinguished Professor at Australia’s Queensland University of Technology (QUT) and the Director of the International Laboratory for Air Quality and Health at QUT, told Reuters.

“You can repeat this experiment without a mask and you will get the same result,” she in an email.

Carbon dioxide molecules are small enough to easily pass through any cloth mask material, the U.S. Centers for Disease Control and Prevention (CDC) explains on its website (here). “Wearing a mask does not raise the carbon dioxide (CO2) level in the air you breathe,” it says.

Chris Iddon is a Research Fellow from the UK University of Nottingham’s Department of Architecture and Built Environment and is working on AIRBODS (Airborne Infection Reduction through Building Operation and Design for SARS-CoV-2), a project establishing how to safely use and ventilate non-residential buildings to minimise the risk of airborne transmission of COVID-19 and other viruses.

“She is measuring exhaled breath,” Iddon agreed after viewing the clip. “The method used in this video is not measuring the inhaled CO2 concentration.”

According to Iddon, because exhaled breath is comprised of around 4% carbon dioxide, or 40,000ppm, it was “not surprising” the CO2 sensor would present this reading.

“You ought to be worried if your exhaled breath doesn’t have a high CO2 content because it would mean that you have ceased to respire!” he said.

A publication from the UK’s Health and Safety Executive(here) advises that when using a monitor to measure CO2, the device must be positioned over 50cm away from the person.

Because exhaled breath contains carbon dioxide, the monitor may give a “misleadingly high” reading if it is too close, it warns.

Dangerous levels of CO2 cannot be trapped inside breathable materials such as cloth or disposable COVID-19 masks because the gas moves straight through the mask with the person’s breath.

“Exhaled air (which contains exhaled CO2), doesn’t accumulate in the mask,” Morawska agrees. “This means that the gas doesn’t accumulate in the mask either as there is no physical process by which it would be selectively accumulating in the mask, while the air doesn’t.”

Reuters has previously fact checked false claims about face masks and CO2 (here) and (here).


False. The device used in the video is measuring exhaled - rather than inhaled - air. Breathing directly onto a monitor, with or without a mask on, will produce a high result. This exhaled air, which contains CO2, does not accumulate in cloth masks because the molecules pass through the material with the air.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts here.