Exhaled carbon dioxide caused by the use of face masks, including the N95 mask, has not been shown to cause carbon dioxide toxicity or lack of adequate oxygen in healthy people. Because the masks we make and purchase, and even the airtight medical masks listed above, are designed for constant breathing, the risks of any side effects are low. Again, for people diagnosed with illnesses such as COPD, emphysema, and obesity, and in heavy smokers, the consistent use of N95-like masks over long periods of time could cause some build-up of carbon dioxide levels in the body. If people in this group are experiencing these side effects, they should speak to their doctor.
The claim that the prolonged use of face masks can cause carbon dioxide intoxication, dizziness, or other health challenges is not grounded in science. In fact, healthcare workers often wear masks for long hours in the hospital. There is no evidence that surgical masks or cloth masks cause significant build-up of carbon dioxide. This information has been primarily circulating on social media among individuals or communities resistant to mask-wearing in general. While masks are restrictive and can feel like they impede air flow, properly designed masks do allow air flow by design, and the feeling of inconvenience or minor discomfort does not equate to health risks such as a build-up of carbon dioxide. Inhaling high amounts of carbon dioxide can be dangerous and lead to hypercapnia (carbon dioxide toxicity), but is extremely unlikely to happen as a result of wearing a mask.
There is some evidence that prolonged use of N95 masks in wearers with particularly severe health conditions, such as lung disease, could cause some build-up of carbon dioxide in the body. However, these cases are rare, and the use of N95 masks is not recommended for the general public in order to reserve them for frontline workers who are at higher risk of exposure to the virus.
We base our COVID-19 expert contextualizations on information provided by internationally-recognized health organizations, public health researchers and infectious disease experts. Because information in epidemics is constantly being updated, our content is up to date based on the date and time they are published. If you’re looking for medical advice, please contact a healthcare provider, and be sure to review the World Health Organization website for more information about COVID-19.