Is It Dangerous to Wear a COVID-19 Protective Mask For Too Long?


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.

What’s True

Breathing in excessive carbon dioxide is dangerous for the body. Some people with preexisting respiratory illnesses may face health issues only with prolonged use of tight-fitting masks, such as respirators. 


What’s False

However, people wearing cloth or surgical masks are in little to no danger of breathing in unhealthy amounts of carbon dioxide.


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 numerous posts stating that wearing face masks can lead to hypercapnia, or excessive carbon dioxide levels in the blood, due to “rebreathing your own CO2”, while other posts claim that the resulting hypercapnia “weakens the immune system”. Posts making a similar claim “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 “Wearing a surgical mask for short periods of time does not impact significantly physiological respiratory variablesand 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, 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.”

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.



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.

“Dr. Dennis A Castro B” wrote in a newspaper Vanguard, for instance, that prolonged use of face masks causes hypoxia: 

The post does not specify what kinds of masks cause these issues (though the article image does show N95 respirator masks), nor does it indicate whether this affects people with respiratory conditions more. It should be noted that hypoxia is a condition in which the tissues of the body are starved of oxygen. 

Another post argued that prolonged mask usage caused hypercapnia, a condition arising from too much carbon dioxide in the blood. 

Symptoms of hypercapnia include dizziness, drowsiness, fatigue, headaches, feeling disoriented, flushing of the skin, and shortness of breath. Severe symptoms include a loss of consciousness, coma, hyperventilation, twitching muscles, and seizures, among others. Preexisting respiratory illnesses like chronic obstructive pulmonary disease (COPD) can cause both hypercapnia and hypoxia

But research articles and experts suggest that such extreme symptoms are unlikely to occur in most people. The risk of hypoxia and hypercapnia are unlikely to take place with cloth and surgical masks, because they are not tight-fitting: 

Some people with pre-existing respiratory illnesses (like asthma, COPD), may face breathing difficulty with use of certain types of tight fitted masks, called respirators. [There is] less chance of hypoxia as they may discontinue using masks in that case. Risk is very low with cloth and surgical masks as they are not tight around [the] face.

He also argued that in the case of prolonged usage of any of these masks, “Dizziness was less likely, but fatigue may occur.”

The N95 respirator is an example of personal protective equipment (PPE) usually worn by health workers to protect the wearer from airborne particles and from liquid contaminating the face. The Centers for Disease Control and Prevention (CDC) does not recommend that the general public use these masks because health workers and other medical first responders need them more. 

A team of Stanford engineers is developing an N95 face mask to counteract the side effects of oxygen deficiency. In an interview, John Xu, a mechanical engineer behind the effort, said:

N95 masks are estimated to reduce oxygen intake by anywhere from 5 to 20 percent. That’s significant, even for a healthy person. It can cause dizziness and lightheadedness. If you wear a mask long enough, it can damage the lungs. For a patient in respiratory distress, it can even be life threatening.

We are targeting this to anyone who has to wear a mask for the long term, first responders, doctors, nurses and even patients who don’t want to infect others. In the near term, we hope to get these into healthcare workers as soon as possible.

The general public is unlikely to wear masks for a prolonged period other than for short stints outside of homes, according to Reuters. A CDC representative spoke to Reuters: 

The CO2 will slowly build up in the mask over time. However, the level of CO2 likely to build up in the mask is mostly tolerable to people exposed to it. You might get a headache but you most likely [would] not suffer the symptoms observed at much higher levels of CO2. The mask can become uncomfortable for a variety of reasons including a sensitivity to CO2 and the person will be motivated to remove the mask. It is unlikely that wearing a mask will cause hypercapnia.

The CDC recommends that the general public wear cloth masks, leaving N95 respirators and surgical masks to healthcare workers. They also offer exceptions for who should be wearing them:

With these recommendations comes the additional guidance that face masks should not be a substitute for social distancing. 

The CDC also responded to Snopes about the impact an N95 respirator would have on healthcare workers: 

In all, little research has been done on the impact of masks on wearers.

In some studies, participants noted breathing difficulties, but not hypoxia. 

Ultimately, the impact of a mask on its wearer depends on the wearer’s health, any pre-existing respiratory illnesses, the type of mask, and the length of time the person wears it. In most instances, the effects of prolonged cloth mask usage are small. Masks, like most short-term measures to prevent the spread of COVID-19, should be worn only if the wearer has to be in close proximity to others, and be used in addition to necessary measures like social distancing, and more. As such, we rate this claim about

A good protective measure against COVID-19 is to wear a face mask—if you’re asymptomatic, face masks can help contain the spread of droplets from your coughs and sneezes. It’s important to keep your face masks clean, especially homemade ones.

Anytime you touch your mask, you wash your hands. So either when you take it off, wash your hands, or sanitize if you have hand sanitizer. Wash your hands. And then when you put it back on, if it hasn’t been just washed, right, then again you would do the same hand hygiene, either washing and/or hand sanitizer.

As you’re taking the mask on and off, look at it as possibly contaminated on the outside. So don’t ever touch the outside of your mask. Okay. When you take it on and off, grab it by whatever. If it’s tied, untie it. Untie the neck first and then the upper. So the lower one first and then the upper one. Place it down, face down, onto like a paper towel or a towel or something so that when you go to put it back on, you again only grab the straps. Don’t touch the mask itself. Put the mask on. You don’t ever want to take the mask, put it below your chin. You don’t want to take your mask, put it on your arm or hang it from your ear or any of those things, because, again, whatever may be on that mask will then be all over those surfaces.

The biggest thing is when you are wearing it, do your very, very best to just leave it on. Don’t take it on and off unless you absolutely have to. The theory there is you have a greater chance of contaminating both yourself and other surfaces if you’re constantly taking that mask on and off.

Luckily, when we’re talking about the COVID-19 virus, it’s an enveloped virus, right, so it has an envelope of lipids on the outside. Pretty easy to break that down and kill it. Heat does it. Soap and detergent do it. So when you’re washing the masks, the hotter you can have the water, the better, and the hotter you can have the air if you’re drying it, the better. And if you add a detergent, good. I’m also . . . at our house, we’re adding vinegar to our laundry, because vinegar has also been shown to help kill the virus.

I recommend washing it every day, depending on how often you have to wear it. Some people aren’t wearing their masks all day, every day. If you wear it for 20 minutes to go to the store, and right now that’s all you’re wearing it and you have a nice safe place to keep it, you could probably do a couple of days before you wash it. The virus doesn’t seem to live super long on cloth. There’s still some information that we don’t know. We don’t know exactly how long that is, but it’s probably not much more than a couple of days at the most.

We were thinking of them in terms of I’m going to put a mask on so you don’t get me infected. But we’re changing the way we’re looking at that, and really I’m going to put a mask on so I don’t infect you even if I don’t have any symptoms, because we now are understanding that people may be able to transmit this virus the day before or a couple of days before they really have that fever, muscle aches, shortness of breath, the coughing type of flu-like symptoms. That’s going to help so that when I go to the store, I’m not spreading it to everybody else. Now, if all of us do that, we’re keeping one another safe, and that’s a great way that we can show our citizenship, our care for one another.

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.

Surgical Masks: … If worn properly, a surgical mask is meant to help block large-particle droplets, splashes, sprays, or splatter that may contain germs (viruses and bacteria), keeping it from reaching your mouth and nose. Surgical masks may also help reduce exposure of your saliva and respiratory secretions to others.

While a surgical mask may be effective in blocking splashes and large-particle droplets, a face mask, by design, does not filter or block very small particles in the air that may be transmitted by coughs, sneezes, or certain medical procedures. Surgical masks also do not provide complete protection from germs and other contaminants because of the loose fit between the surface of the face mask and your face.

N95 Respirators: An N95 respirator is a respiratory protective device designed to achieve a very close facial fit and very efficient filtration of airborne particles.

The ‘N95’ designation means that when subjected to careful testing, the respirator blocks at least 95 percent of very small (0.3 micron) test particles. If properly fitted, the filtration capabilities of N95 respirators exceed those of face masks. However, even a properly fitted N95 respirator does not completely eliminate the risk of illness or death.

The CDC elaborated on the purpose of wearing homemade cloth masks during the COVID-19 pandemic. The CDC writes that since many people with coronavirus may be “asymptomatic,” meaning that they don’t show any symptoms, wearing a cloth mask can prevent these contagious individuals from unknowingly spreading the disease:

CDC continues to study the spread and effects of the novel coronavirus across the United States. We now know from recent studies that a significant portion of individuals with coronavirus lack symptoms (“asymptomatic”) and that even those who eventually develop symptoms (“pre-symptomatic”) can transmit the virus to others before showing symptoms. This means that the virus can spread between people interacting in close proximity—for example, speaking, coughing, or sneezing—even if those people are not exhibiting symptoms. In light of this new evidence, CDC recommends wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies) especially in areas of significant community-based transmission.

It is critical to emphasize that maintaining 6-feet social distancing remains important to slowing the spread of the virus. CDC is additionally advising the use of simple cloth face coverings to slow the spread of the virus and help people who may have the virus and do not know it from transmitting it to others. Cloth face coverings fashioned from household items or made at home from common materials at low cost can be used as an additional, voluntary public health measure.

The cloth face coverings recommended are not surgical masks or N-95 respirators. Those are critical supplies that must continue to be reserved for healthcare workers and other medical first responders, as recommended by current CDC guidance.

When we reached out to the CDC, a spokesperson reiterated this point, saying that wearing a mask is a good way of “strengthening the social distancing that we are already doing.”

A spokesperson for the CDC told us:

“As we study the virus, CDC has learned that a good proportion of individuals who have COVID-19 spread virus before they become symptomatic and a few people never have symptoms at all but are still infected and infectious. That means, that people who are not coughing or sneezing can be a source of infection for others. Something simple like speaking is enough to generate aerosols that can spread the infection to other people.

A simple cloth mask is a way to contain respiratory secretions right at the source and not put other people at risk. The mask traps the droplets before they spread into the environment. Therefore, “my mask protects you, and your mask protects me!” It’s a way of strengthening the social distancing that we are already doing.

The numbers provided in the above-displayed viral social media post are also suspiciously specific. While there have been studies regarding the efficacy of masks during COVID-19 pandemic, researchers are still learning about how this disease spreads and how to best prevent it. For instance, Live Science noted that two recent studies regarding the efficacy of face masks during this pandemic came to slightly different conclusions. 

Live Science writes:

For the first time, the Center for Disease Control and Prevention (CDC) has recommended that even seemingly healthy people wear masks over their mouths and noses when venturing out of their homes into places where it is difficult to maintain distance from other people. But there is still major debate over how much masks — particularly the homemade fabric masks that the CDC recommends for the public — can slow the spread of SARS-CoV-2, the virus that causes COVID-19.

Researchers, writing in two new papers, attempt to tackle the efficacy of masks, one more rigorously than the other, and come to differing conclusions. One study examined the effect of masks on seasonal coronaviruses (which cause many cases of the common cold) and found that surgical masks are helpful at reducing how much virus a sick person spreads. The other looked particularly at SARS-CoV-2 and found no effect of either surgical or fabric masks on reducing virus spread, but only had four participants and used a crude measure of viral spread.

The bottom line, experts say, is that masks might help keep people with COVID-19 from unknowingly passing along the virus. But the evidence for the efficacy of surgical or homemade masks is limited, and masks aren’t the most important protection against the coronavirus.

Some experts have also expressed concern that widespread use of homemade cloth masks give people a false sense of security. The White House’s coronavirus response coordinator, Dr. Deborah Birx, said that social distancing is still the most important preventative measure a person can take during this pandemic:

“The most important thing is the social distancing and washing your hands,” she said. “And we don’t want people to get an artificial sense of protection because they’re behind a mask. Because if they’re touching things — remember your eyes are not in the mask — so if you’re touching things and then touching your eyes you’re exposing yourself in the same way.”

The World Health Organization (WHO) reiterated this point. WHO said in a statement that “masks alone cannot stop the pandemic:” “Masks alone cannot stop the pandemic. Countries must continue to find, test, isolate and treat every case and trace every contact. Mask or no mask, there are proven things all of us can do to protect ourselves and others – keep your distance, clean your hands, cough or sneeze into your elbow


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.”


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