This is How a Face Mask Protects from Covid-19?

Two months ago, only Asian tourists and pollution-conscious cyclists wore masks on the streets in Britain. But Covid-19 has changed that. In any queue to enter a grocery shop, you see many faces garnished with everything from re-used painters masks to coloured improvised ones.

According to the UK government, the World Health Organisation (WHO), Public Health England and many academics, there is no need to wear one. Yet a few other countries, like Austria, the Czech Republic, Slovenia, Japan and Italy, are requiring the public to use masks when outside their home. The Centre for Disease Control (CDC) in the US is considering changing its direction on masks, it has been reported, while the WHO is now reviewing the evidence in light of recent data from Hong Kong. "There are differences between countries, and that confuses people," Elaine Shuo Feng, a researcher at the University of Oxford, and author of an article in the medical journal The Lancet inviting for responsible use of face masks during the pandemic.

While it is the time to follow experts, they don't all agree on the use of masks. Researchers publishing in the British Medical Journal highlighted the discrepancies in the WHO's own guidance, including the contradiction in encouraging face masks to hospital staff and no one else.

If they work for doctors, why wouldn't they be useful for anyone else?

Part of the problem is a lack of study, but one point is clear: masks are not a substitute for social distancing, staying two meters apart, or washing hands. Whatever the public health experts in a country think about masks, they should be used only in addition to those other measures. Yet what do we know about how effective face masks are in protecting us against viruses?

While the WHO has new evidence on the matter, there are past studies that suggest how beneficial face masks are – or aren't. A study in 2009 discovered that proper hand-washing combined with wearing face masks served to reduce the spread of flu inside households. Still, researchers couldn't isolate the impact of the two. Researchers, in 2013, put surgical masks on a dummy connected to a breathing simulator, finding a reduction in exposure of 6.6 times, depending on the variety of mask. A precise review of several studies of various interventions used during the Sars epidemic suggested using a mask was more effective than washing hands at preventing the virus transmission. However, some of the studies involved were at medical facilities, where people would have professional-grade masks used correctly.

So far, so good.

But we also have the evidence to the opposite.

A study of students in university halls revealed masks alone didn't prevent community transmission of flu, though the hand-washing and masks together did. A meta-analysis of personal protective measures against influenza of 2017 suggested hand washing had a notable protective impact, while masks had a non-significant shielding impact. An analysis of studies made by researchers at the Health Protection Agency (before it became Public Health England) suggested that mask use was correlated with a decreased risk of Sars but not influenza.

That study, from 2011, highlighted an essential need for carefully produced studies outside a crisis situation. And, here we are. Although the researchers noted such work wasn't easy to accomplish, not at least because such a study would need a control group without protective measures.

It may seem alarming that we just don't know if face masks stop community transmission, but we often work with less than complete information. That two-metre rule? It's based on studies from 80 years ago about how far droplets travel. Recent studies suggest they can go much further, which implies that staying two metres apart may not be sufficient to completely prevent the spread of Covid-19, though it will lower infections. We often don't have complete data, but rely on the best information at the time.

Given how little we know about it, why do some public health organisations actively advise against them? There are three main concerns: stockpiling, a false sense of protection, and dangers of misuse.

Shortages of masks

Much of the hesitation around face masks from health agencies seem to come from doubts that official guidance for wearing a mask will spark stockpiling making it more difficult for medical staff and other key workers to obtain professional-level protection.

We know that shortages exist; therefore, supply concerns are justified, but it raises the question of whether public health guidance should be dictated by government failure to secure supply or solely by science. If we should all wear masks, let's all wear them – though the NHS and other frontline workers need to be at the front of the queue.

Of course, there are additional masks available, beyond the respirator-style types, including surgical masks, the rectangular pieces of green material with the two loops for around your ears. And there are handmade types made using leftover fabric or shopping bags. Unfortunately, there are no studies on how they could reduce transmission in the community, but from theoretical considerations, there's some indication it's better than nothing, many would says.

However, William Keevil, professor of environmental healthcare at the University of Southampton, says: "People must stay at home, but if they need to go out, the homemade masks are pretty useless."

One study suggests masks which are made from old t-shirts did reduce droplet transmission, but they should only be considered a "last resort," the researchers said, as surgical face masks were three times better. "Our research showed that they do seem to block some of the microbes that people expel from coughing. Although we only observed at bacteria tested from healthy volunteers so not directly similar with Covid-19. Also, they might support lower exposure from infected people," says Anna Davies, one of the authors of that study. "But there are numerous variables behind [handmade masks] – material, fit, wearer usage, the impact of long term wear on efficiency, decontamination – and so few studies as to their efficacy, that I can see why officials aren't rushing to support extensive use."

Mask may give people a deceptive feeling of protection

Another concern is that masks could wrongly make people think they can go outside without risking to get infected, abandoning social distancing and other fundamental precautions when they should not.

"I've heard some experts saying that using a face mask may give people a deceptive feeling of protection, that jeopardises the impact of social distancing," virologist Ilaria Capua, says. "But this is just a hypothesis. We don't have evidence on this." Again, distancing precautions and hand washing is more important than a face mask, but consider of all those people stuck on packed trains, or forced to go to Tesco to get food because there are no home-delivery appointments.

This raises another issue.

At the core of the mask-wearing puzzle is explaining their purpose: is it to protect those wearing it from infection, or other people? Masks may stop us from touching our faces, which could further reduce the risk of getting infected, but the other direction may be more critical. It's not about you, but it is about protecting other people in the case, you're infected.

And if we're infected and asymptomatic, which is probable with Covid-19, then everyone using a mask may reduce his chance of infecting others by limiting us from spluttering virus-ridden droplets on the Tube or bus. "We know there's asymptomatic transmission of COVID-19. People may spread the virus before they experience any symptoms.

The third worry with face masks is that people don't wear them correctly.

Professional masks, such as the N95, need to be correctly fitted and should be given to medical staff anyhow. But if you have an extra protection mask leftover from some DIY work or have made one yourself, you still want to know how to put it on and remove it safely, or instead of minor benefits may incur serious risk.

A study in 2015 found cloth masks could actively spread disease, but the researchers have since written an update to explain that perhaps it was because they were poorly cleaned.

If you're going to use a mask, wash your hands before and after putting it on, and then don't touch it. It should fit firmly around your face and cover your nose. To remove a face mask, take it off by the loops around your ears, without touching the front, and then either wash it carefully or dispose of it. As always, wash your hands at the end. You regularly see people feeling these masks because they don't fit properly. If the mask has filtered virus, you end up putting the virus on your hands by touching it.

Because of these concerns and the scarcity of robust data, it's no surprise health officials are struggling with clear advice, but we need it because people are using them anyhow. Because of the real risks increased by wrongly wearing a mask, we need general, clear information about how to do it properly. Wearing or not wearing a mask is a personal choice. Wear a face mask if you want to protect others, but do it the correct way, and always wash your hands.