11/05/2020: This article has been updated in line with the new government guidance regarding face masks.
Currently, the World Health Organisation recommends that, outside of healthcare professionals, people should only wear masks if they display symptoms of COVID-19 or are taking care of someone who does.
On 11 May, the government released a document entitled Our Plan to Rebuild, in which it says that “people should aim to wear a face-covering in enclosed spaces where social distancing is not always possible,” and that “Homemade cloth face-coverings can help reduce the risk of transmission in some circumstances.”
Can face masks stop the spread of COVID-19?
Unfortunately, at the minute, we simply don’t know enough about COVID-19 to say definitively whether wearing a face mask could stop you from catching or spreading the virus.
“The problem with the new coronavirus is that there’s too little information about exactly how it’s spread, because it’s so new,” says Dr Alexander Edwards, associate professor at the School of Pharmacy at the University of Reading. “For example, we don’t know if it’s spread more effectively through contact, versus being spread through aerosols, so basically, coughs.”
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The trouble is that it’s difficult to study how the virus is passed from person to person. Theoretically, the best way to study COVID-19 transmission would be to expose people to a contaminated aerosol or a virus-laden surface and see how many get infected. But this could never be ethical.
Instead, biologists have to make do with more circumspect methods. One study from MIT used high-speed cameras to track the droplets expelled in coughs and sneezes. They found that puffs of air carry droplets for up to six or eight metres, for coughs and sneezes respectively.
Another study, conducted by aerosol specialist Dr Boris Gorbunov, found that taking wind conditions into account could bring the distance a cough travels up to 25 metres.
Researchers at Hong Kong University and the University of Maryland took another approach. For a study published in Nature Medicine on 3 April, they looked at patients with other coronaviruses – the seasonal ones that cause the common cold – along with influenza and rhinoviruses.
The researchers collected droplets from the patients’ breath with and without a surgical face mask and counted how many copies of the virus were present. Three out of 10 coronavirus patients had a detectable viral load in their breath without a face mask, compared to none when wearing one.
“It makes perfect sense that if you wear a mask over your face, when you cough, you might expect that that mask would reduce the spread of that cough,” Edwards says. “We don’t actually know how much that reduces it, but the idea of a face mask is a good one.”
Why weren’t we advised to wear face masks before?
Whether coronavirus is transmitted primarily by touch or by coughs and sneezes is an important factor. “One of the reasons that people wear masks is they think that it’s going to protect them from the virus. But the virus isn’t floating around in the air,” Dr Shunmay Yeung of the London School of Hygiene and Tropical Medicine told the BBC.
“It’s probably going to be on my hand because of shaking hands with someone who’s got the virus, and I have transmitted it. I have carried the virus to my face.”
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Simply wearing a mask won’t eliminate your risk of catching or spreading the virus. “Remember that some face masks are designed, when you breathe out, to let the air go out as normal, and they only filter the air when you breathe in,” Edwards says. “And a face mask is only as good as it fits.”
A face mask may reduce your risk, even if it doesn’t remove it completely, but this is an important distinction. It’s vital that people don’t become complacent because they think they’re protected by a mask. Even the best mask can’t replace social-distancing and good hygiene.
So, should we be wearing face masks?
“I don’t think it’s a bad idea, so long as people understand that they are not magic shields,” Edwards says. If you do wear one, Edwards suggests you keep yourself and those around you safe by behaving as though it doesn’t work.
Finally, make sure that you’re not depriving anyone of the personal protective equipment they really need. “We know that there are healthcare workers in the front line who are often working without proper protection, or running out of face masks,” Edwards says. “I would certainly not waste them unless you absolutely know that when you wear it, you’re really gaining some benefit.
“And there’s a really important point there, which is that if you have any symptoms, don’t go out!”