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No, face masks don’t reduce oxygen in blood – and won’t kill you

This article is more than 4 years old

A Facebook post warning of the “danger of facemask” claims that masks are “supposed to be used for a limited time”.

This, it says, is because they reduce oxygen “in the blood” and “to the brain”, cause weakness – and “may lead to death”.

People in several countries have been advised to wear some form of face mask to help slow the spread of Covid-19.

South Africa’s risk adjusted strategy to control the disease requires people to wear cloth masks when they’re away from home. Kenya has also made masks mandatory in public.

But is it dangerous to wear them too much?

Blood oxygen levels

A low level of oxygen in the blood is known as hypoxemia. This can cause hypoxia, in which the body is starved of oxygen.

This is dangerous, because our bodies need oxygen to function. As explained by the US-based academic hospital Cleveland Clinic, hypoxemia may cause several symptoms, including headaches, shortness of breath and confusion. In extreme cases, it can eventually become fatal.

The Facebook post includes a photo of a commonly used disposable face mask. But there’s no evidence that these masks dangerously lower blood oxygen levels.

For masks to cause hypoxia, they would have to be hermetically glued to our skin, an expert told fact-checking organisation AFP, which also debunked this claim.

Masks and respirators

Disposable masks and surgical masks are very different to N95 respirators. The respirators are specialised equipment that filter pathogens such as TB bacteria out of the air.  

As we explain in our guide to face masks, surgical masks and N95 respirators should only be used by medical staff, who really need them. Everyone else should wear cloth masks, which are less effective at filtering the air, but do give some protection.

Even medical masks and respirators, much more effective filters, have not been associated with lower blood oxygen content. Two studies of healthcare workers showed no drop in blood oxygen levels in patients wearing either surgical or N95 masks. But the studies were small, testing only 10 and 20 subjects.

In a slightly larger study of 87 healthcare workers, test subjects reported increased levels of discomfort after wearing surgical masks and N95 respirators for three hours. But the study did not say blood oxygen levels were a concern.

It found that N95 masks could affect breathing, but that this was mostly due to factors such as “different temperatures and humidification on outer and inner mask surfaces”, issues that were limited with surgical masks. They should be even less of a concern with cloth masks.

Masks can pick up germs

Individual masks and N95 respirators should be worn for a limited time, but this has nothing to do with oxygen. It’s because with use they can pick up viruses and bacteria. As the US Centers for Disease Control says: “The most significant risk is of contact transmission from touching the surface of the contaminated respirator.”

This risk is why people who care for Covid-19 patients, such as healthcare workers, are advised to wear disposable masks, and discard the masks after they have seen each patient.


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