Should you be wearing a face mask? Scientists still aren’t sure

Two months ago, the only people wearing masks on British streets were Asian tourists and pollution-wary cyclists. But Covid-19 has changed that: in any two metre-spaced queue to enter a shop, there’ll be plenty of faces adorned with everything from repurposed dust masks to brightly coloured handmade ones.

We don’t need to wear masks, according to the British government, the World Health Organisation (WHO), Public Health England or many academics. But plenty of other countries, from Austria and the Czech Republic to Slovenia and Japan, are ordering the general public to don masks in crowded places. The US Centre for Disease Control (CDC) is reportedly considering changing its guidance against masks, while the WHO is now reconsidering the evidence in light of fresh data from Hong Kong. “There are discrepancies between different countries, and I think that confuses people,” says Elaine Shuo Feng, a researcher at the Oxford Vaccine Group at the University of Oxford, and author of a comment piece in medical journal The Lancet calling for rational use of face masks in the pandemic.

While now is very much the time to listen to experts, they don’t all agree when it comes to masks – researchers writing in the British Medical Journal highlighted the inconsistencies in the WHO’s own guidance, including the contradiction between advising masks for hospital staff but no one else. If they work for nurses, why wouldn’t they be beneficial for anyone else?

Part of the problem is a dearth of research, but there is one point with clarity: masks are not a substitute for social distancing, keeping two meters apart, or carefully washing hands. Regardless of what a country’s public health experts think about masks, they should only be used in addition to those measures. But what do we know about how helpful masks are at protecting us from viruses?

While the WHO has new data on the subject, there are older studies that suggest how useful masks are – or aren’t. A study in 2009 found that hand washing combined with face masks helped reduce the spread of flu within households, but researchers couldn’t separate the impact of the two precautions. In 2013, researchers put surgical masks on a dummy attached to a breathing simulator, finding reduction in exposure fell by an average of 6.6 times, depending on the type of mask. A systematic review of different studies of various interventions used during the Sars outbreak suggested wearing a mask was more effective than washing hands at stopping the transmission of the virus, though some of the studies included were at medical facilities, where people would have professional-grade masks worn correctly.

So far so good. But then we have the evidence to the contrary. A study of students in university halls showed masks alone didn’t stop community transmission of influenza, though the combination of handwashing and masks did. A meta-analysis of personal protective measures against influenza published in 2017 suggested hand washing had a significant protective effect, while masks had a non-significant protective effect. A review of studies by researchers at the Health Protection Agency (before it was renamed Public Health England) suggested that mask use was associated with a reduced risk of Sars but not influenza.

That study, from 2011, highlighted an urgent need for carefully designed studies “conducted outside a crisis situation” – yet, here we are – though the researchers noted such work wasn’t easy to accomplish, not least because such a study would require a control group without any protective measures.

It may sound alarming that we simply don’t know if face masks prevent community transmission, but we often operate with less than perfect information. That two-metre rule? It’s based on studies published 80 years ago about how far droplets can travel. More recent studies suggest they can travel further, which means that keeping apart by two metres may not be enough to entirely halt the spread of Covid-19, though it will reduce infections. We often don’t have perfect information, but rely on the best knowledge at the time.

Given how little we actually know with regards to masks, why do some public health bodies actively warn against them? There are three main fears: stockpiling, a false sense of security, and risks of misuse.

Much of the reticence around masks from health agencies seems to come from fears that official guidance to wear a mask will spark stockpiling making it harder for frontline medical staff and other key workers to access professional-level protection. “They should be preserved for healthcare workers only,” says Feng of respirator-style masks, such as those rated N95 or FPP3, which filter out some of the smallest airborne droplets.

Given shortages already exist, supply concerns are clearly warranted, but it raises the question of whether public health guidance should be driven by failures of government to ensure supply or merely by science. If we should all have masks, let’s all have masks – though the NHS and other other frontline workers clearly need to be at the front of that queue.

Of course, there are other masks available, beyond those respirator-style models, including surgical masks, the rectangular pieces of blue or green material with the two loops that go around your ears. And there are handmade versions, with efforts to sew masks for medical staff and designs using leftover fabric or shopping bags. “Unfortunately we don’t have studies of how [handmade masks] could reduce transmission in community, but from mechanistic studies, there’s some evidence it’s better than nothing,” Feng adds. “People should stay at home, but if they have to go outside, those homemade masks should be better than nothing.” William Keevil, professor of environmental healthcare at the University of Southampton, disagrees, calling them “pretty useless.”

One study suggests masks made from old t-shirts did reduce droplet transmission, though the researchers said they should only be considered a “last resort,” as surgical masks were three times better. “Our study showed that they do appear to block some of the microbes that are expelled from coughing – although we only looked at bacteria sampled from healthy volunteers so not directly comparable with Covid-19 – and they might help lower exposure from infected individuals,” says Anna Davies, one of the authors of that study. “But there are so many variables behind [handmade masks] – material, fit, wearer usage, effect of long term wear on efficacy, decontamination – and so few studies as to their efficacy, that I can see why policy makers aren’t rushing to advocate widespread use.”

There’s another concern that masks will incorrectly make people feel they can go outside without risking their safety, forgoing social distancing and other precautions when they should not. “I’ve seen some experts saying that wearing a face mask may give people a false sense of security, that jeopardises the effect of social distancing,” says Feng. “But this is a hypothesis. I don’t think we have evidence on this.” Again, distancing precautions and hand washing are more important than a mask, but think of all those people stuck on crowded trains, or forced to go to Tesco for supplies because they can’t get a home-delivery appointment.

This raises another issue. At the core of the mask-wearing conundrum is understanding their purpose: is it to protect the person wearing it from infection, or other people? Masks may stop us touching our own faces, which could help reduce the chance we get infected – but the other direction may be more important. It’s not about you, but protecting other people in case you’re infected. That’s more often than not why they’re worn in Asia, says Keevil. “It’s actually a courtesy,” he says. “The wearer believes they may be infected and don’t want to infect anybody else.”

And if we’re infected but asymptomatic – which is possible with SARS-CoV-2, with symptoms not necessarily showing for as long as ten days – then everyone wearing a mask may reduce others from being infected by preventing us from spluttering virus-ridden droplets on the Tube or in Tesco. “We know there’s asymptomatic transmission of COVID-19,” says Feng. “People may spread the virus before they have their first symptoms.”

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The third concern with masks is that we don’t wear them correctly. Professional masks, such as the N95, need to be properly fitted – and should be handed over to medical staff anyway. But if you have a spare safety mask left over from a DIY project or have made one yourself, you still need to know how to put them on and remove them safely, or the minor benefits may be traded for serious risk. A study in 2015 found cloth masks could actively spread disease, but the researchers have since written an update to explain that may be because of how poorly they were cleaned. “I think we’re creating more risk,” says Keevil, by wearing masks.

If you’re going to wear a mask, wash your hands before and after putting it on, and then don’t touch it. It should fit snugly around your face and cover your nose. To remove a mask, take it off by the loops around your ears, don’t touch the front, and then either dispose of it or wash it carefully. And then, as always, wash your hands. But that’s not what many people do, says Keevil. “You regularly see people touching these masks because they don’t fit properly,” he says. “If the masks have filtered any virus, you just put the virus on your hands by touching them.”

Given those concerns and the lack of robust science, it’s no wonder health authorities are struggling with official advice – but we need it, because people are wearing them anyway. Because of the real risks raised by incorrectly donning a mask, we need widespread, clear advice about how to do it safely. “Wearing or not wearing a face mask is a personal choice,” Feng adds. Wear a mask if you want to protect other people, but do it the right way – and wash your hands no matter what.

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