Wearing face masks does not cause hypercapnia or affect the immune system

Wearing face masks can cause carbon dioxide toxicity; can weaken immune system
Incorrect: Face mask filters are small enough to keep out infectious droplets containing viruses, but gas molecules such as carbon dioxide and oxygen can still pass through freely. Healthcare workers who wear masks for long periods of time do not demonstrate significant impairment in work performance, as would be the case if masks did cause hypercapnia.
Unsupported: There is no scientific evidence supporting the claim that the use of face masks weakens the immune system.
Face masks help to limit contact with infectious droplets which carry pathogens. However, the material used for face masks are still porous enough to allow gas molecules, such as carbon dioxide and oxygen, to pass through, and do not significantly impair gas exchange to the point of causing hypercapnia. No scientific evidence supports the claim that the use of face masks weakens the immune system.

FULL CLAIM: Wearing face masks can cause carbon dioxide toxicity; can weaken immune system


This claim circulated on Facebook in late April 2020 in the form of posts suggesting that wearing face masks can lead to hypercapnia, or excessive carbon dioxide levels in the blood due to “rebreathing your own CO2”, accompanied by images like this one. Other posts, like this one, further claim that the resulting hypercapnia also “weakens the immune system”. Posts making a similar claim about the immune system have also cited Judy Mikovits, who claimed that “masks will hamper oxygen intake” and reduce immunity.

The claim does not specify which types of face masks it refers to. In healthcare settings, the two main types of masks used are surgical masks and N95 masks. N95 masks, named for their ability to filter out at least 95% of airborne particles, are also called respirators. Of the two, N95 masks have a tighter fit and thus provide more protection than surgical masks. The purpose of these masks is to reduce contact with infectious droplets (aerosols), which can be generated by someone who coughs or sneezes, and thereby minimize the risk of infection transmission. These masks have become of particular importance given the COVID-19 pandemic.

While it is true that hypercapnia can be life-threatening, the claim that it can be caused by wearing face masks, either surgical masks or respirators, is unsupported and runs contrary to existing evidence. The masks act as a barrier to keep out aerosols, but the materials used are still porous enough to allow gas molecules like carbon dioxide and oxygen to pass through, which are many times smaller than viruses. The size of a carbon dioxide molecule is estimated at about 230 picometers. In contrast, SARS-CoV-2, the causative agent for COVID-19, is about 60 to 140 nanometers[1], which is at least 10,000 times larger.

Sofia Morra, a cardiologist at the Erasme University Hospital in Brussels, explained to Health Feedback, “Wearing a surgical mask for short periods of time does not impact significantly physiological respiratory variables[2] and thus, whenever a rise in CO2 occurs in the ‘dead space’ of the mask, it is unlikely that the magnitude of this increase would be sufficient to to impair immune, neurological, or cardiovascular homeostasis.”

The claim is also clearly contradicted by empirical evidence. Healthcare workers wear both types of masks for long hours at work without reported impacts to their work performance. Hypercapnia causes symptoms such as dizziness, confusion, and loss of consciousness, which would have occurred had they been affected by CO2 toxicity. Victoria Forster, a cancer researcher at the Hospital for Sick Children in Toronto stated the same in this Forbes article:

Take surgeons, for example—during long procedures, they wear surgical masks for hours with no ill-effects on their carbon dioxide levels. Having a surgeon with an altered mental state would not be in the best interests of either the patient or the surgeon and thankfully, this simply does not happen.

The claim that wearing masks would weaken the immune system is also unsupported by scientific evidence. Prolonged wearing of face masks can cause problems such as discomfort, skin irritation, and even pressure ulcers[3], however immunodeficiency is not among the problems caused by prolonged face mask use.

The U.S. Centers for Disease Control and Prevention (CDC) have stressed that the use of surgical masks and N95 respirators are best reserved for healthcare workers due to limited supply, although it encourages the general public to use cloth masks in public spaces. These have a much looser fit compared to surgical masks and respirators, and are much more porous, making cloth masks even less likely to cause hypercapnia as stated in the claim. However, the CDC does caution that “Cloth face coverings should not be placed on young children under age 2, anyone who has trouble breathing, or is unconscious, incapacitated, or otherwise unable to remove the mask without assistance.” Furthermore, those who decide to use a mask should also exercise caution when removing the mask, as infectious aerosols may potentially contaminate the external and internal surfaces. The U.S. CDC has advised that cloth masks should be regularly washed, and that individuals should wash their hands and avoid touching their eyes, nose and mouth after removing their mask.

A much more likely cause of hypercapnia and asphyxia that the general public should be aware of is covering one’s face with plastic. Because plastic is not porous enough to allow for quick air exchange, unlike face masks, it poses a genuine suffocation risk as cases in the past have demonstrated, and warning labels on plastic bags are used to remind people of this risk.

In summary, it is extremely unlikely that wearing a mask could lead to an increase in carbon dioxide within the area between the mask and face to the extent of causing hypercapnia. While face masks can keep out infectious aerosols, they are porous enough to allow oxygen intake and allow the escape of carbon dioxide. The idea that wearing face masks weakens the immune system is not supported by scientific evidence. This article published on The Conversation illustrates how wearing even a cloth face covering can help to limit the spread of COVID-19 by blocking infectious droplets, which is the main mode of disease transmission.


Sofia Morra, Cardiologist, Erasme University Hospital, Université Libre de Bruxelles:
In this unprecedented time, as SARS-CoV-2 has brought the world to a standstill and strained healthcare systems worldwide, Facebook posts claiming that wearing a face mask can cause carbon dioxide toxicity and weaken the immune system, are spreading, let’s say, as fast as the virus. Posts that make statements such as: “Masks inhibit oxygen intake and increase CO2 intake, lowering efficiency of the human immune system, and do not stop viruses” or “Hypercapnia can be caused by rebreathing your own exhaled CO2 by wearing a mask continuously” can be found more and more on the Web.

It is unfortunate that these posts are not supported by rigorous scientific evidence. Indeed, wearing a surgical mask for short periods of time does not impact significantly physiological respiratory variables[2] and thus, whenever a rise in CO2 occurs in the “dead space” of the mask, it is unlikely that the magnitude of this increase would be sufficient to impair immune, neurological, or cardiovascular homeostasis. Further large-scale studies are required to verify the effect of wearing a mask for a longer period: indeed, while one possible outcome of wearing face masks is the retention of carbon dioxide, another possible outcome could be excessive ventilation leading to hypocapnia, that is, a state of reduced carbon dioxide in the blood.

Until these studies are available, making such claims without supporting scientific evidence is hazardous and dangerous, especially in this very historical moment.


This claim has been fact-checked by Snopes and Africa Check. Snopes rated it “Mostly False” while Africa Check concluded that “No, face masks don’t reduce oxygen in blood—and won’t kill you.”



Published on: 13 May 2020 | Editor:

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