Does Wearing a Face Mask Reduce Oxygen—and Can It Increase CO2 Levels?

With the Centers for Disease Control and Prevention (CDC) recommendation to wear a face mask to help prevent the spread of COVID-19, some people felt that wearing a mask reduced their intake of oxygen—or forced them to breathe in their own carbon dioxide. This left them feeling faint, light-headed, or "smothered." They were also concerned about how dangerous this might be, and how less oxygen and more carbon dioxide might affect their health.

One driver who crashed his SUV into a pole in Lincoln Park, New Jersey, on April 23, 2020, actually blamed his collision on his mask. He told police he passed out because he'd been wearing an N95 mask for too long. Initially, the investigating officers believed him, writing in a Facebook post that he was the only person in the car and passed out due to "insufficient oxygen intake/excessive carbon dioxide intake."

The post was shared more than 2,700 times and received hundreds of comments, with a few sharing their own experiences of feeling smothered by this type of mask. The police department later updated their post, stating that they didn't know "with 100% certainty" that "excessive wearing" of an N95 mask was a contributing factor to the accident. They added that "it is certainly possible that some other medical reason could've contributed to the driver passing out."

So is it possible that wearing a face mask to prevent the spread of COVID-19 could cause someone to build up so much carbon dioxide and get so little oxygen that they pass out—or worse? Carbon dioxide is a natural by-product of the body's respiration process, something we all breathe in and out every day. How harmful can it be?

In rare cases, it can actually be pretty dangerous, according to the National Institutes of Health (NIH). They say that inhaling high levels of carbon dioxide (CO2) may be life-threatening. Hypercapnia (carbon dioxide toxicity) can also cause headache, vertigo, double vision, inability to concentrate, tinnitus (hearing a noise, like a ringing or buzzing, that's not caused by an outside source), seizures, or suffocation due to displacement of air.

But the emphasis here should be on high levels. "It has to be a pretty high concentration to be capable of causing harm," Bill Carroll, PhD, an adjunct professor of chemistry at Indiana University, Bloomington, told Health. "CO2 is present in the atmosphere at a level of about 0.04%. It is dangerous in an atmosphere when it is greater than about 10%."

It's also possible to have too little CO2. "This is when you exhale too fast or too often," said Carroll. "If you hold your breath, you wind up with too much CO2. The core issue is that CO2 regulates the pH of the blood—too much CO2 and the blood becomes too acidic; too little and it becomes too basic (alkaline). In either case, your body detects the change in acidity and you pass out, which is the body's way of saying, 'please stop fooling with me and breathe normally.'"

When it comes to face masks, we know they're not all made equally. The extent to which a mask could affect CO2 levels depends on what it's made of and how tightly it fits.

"If you put a plastic bag over your head and tie it tight around your neck, no coronavirus could get in, but neither could any oxygen and you would suffocate, so we obviously don't recommend that," said Carroll. "I think it's highly unlikely that you would pass out from a lack of oxygen with a cloth mask, which generally doesn't fit tightly to your face. When you exhale or inhale, air can go around the mask as well through the pores in the material. This is why a cloth mask does not absolutely protect you from inhaling the virus, but by disturbing your exhalation flow it tends to protect those around you from aerosols in your breath."

Carroll doubted that any cloth face covering would ever fit against the face so tight that someone would pass out from a lack of oxygen. "You'd take it off because it's uncomfortable well before that happens," he said.

But what about the guy in the New Jersey car crash? After all, he was wearing an N95 mask, not just a regular cloth mask.

"Someone wearing an N95 mask for a prolonged period of time may have alterations in their blood chemistry that could lead to changes in level of consciousness if severe," infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, told Health. But it's most likely to happen to those already predisposed to breathing difficulties, such as smokers, obese people, or individuals with COPD or emphysema.

Kelli Randell, MD, an internist and medical advisor at Aeroflow Healthcare, told Health that prolonged use of any face mask, including the N95 respirator, has not been shown to cause carbon dioxide toxicity in healthy people. "Because breathing is slightly harder with a mask, I do recommend that people who suffer from severe COPD or other lung diseases that make breathing difficult carefully consider the use of face masks," said Dr. Randell.

Dr. Adalja added that the N95 respirator is a type of personal protective equipment (PPE) designed to protect health care workers and the patients they care for. "It's uncomfortable to wear, and it does restrict your breathing," said Dr. Adalja. "When I wear one to take care of patients I try to keep it on only for as long as I have to."

The bottom line? The CDC recommends you "wear a mask with the best fit, protection, and comfort for you." The agency also provides guidelines to help you decide when to wear a mask and what type to consider—like if you're sick and have to be around other people or if you're caring for someone who's ill (in which case, they state that a respirator will provide the most protection). If you feel like your airways are cut off while wearing a mask, consider other possible causes, such as a panic attack, which can trigger sudden feelings of suffocation and breathlessness.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.