9 April 2020
As cases of covid-19 continue to rise, many people are choosing to wear a face mask when out in public – but do they work?
Guidance on face masks varies wildly among international health bodies and governments. The World Health Organization (WHO) currently only recommends face masks for people who are coughing or sneezing, or for those who are caring for people who are suspected to have covid-19.
In some places like Lombardy, the worst hit region of Italy, face masks are mandatory. The UK government doesn’t recommend widespread use of them, while as of 3 April, the US Centers for Disease Control and Prevention recommend that people wear “cloth face coverings” when they go out – and even provide instructions for how to make one.
Part of the reason for recommending homemade face masks is to reserve the limited supplies of medical face masks for healthcare workers, some of whom have had to resort to covering up with bin bags, snorkels and office supplies bought from craft stores due to shortages.
Some have also been using cloth face coverings, but these aren’t up to the job, says Raina MacIntyre at the University of New South Wales in Sydney.
In 2015, MacIntyre and her colleagues ran a clinical trial pitting cloth masks against medical ones. The team provided 1607 healthcare workers at 14 hospitals in Hanoi, Vietnam, with either disposable medical masks or reusable cloth ones, which could be washed at home at the end of the day they were worn. Those that wore cloth masks were significantly more likely to catch a virus, the team found.
But what about the rest of us? In an attempt to answer this question, Paul Hunter at the University of East Anglia, UK, and his colleagues looked at 31 published studies on the efficacy of face masks.
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Overall, the evidence suggests there may be a small benefit to wearing some kind of face covering. They do seem to prevent sick people from spreading the virus, but the evidence is weak and inconsistent, says Hunter.
“Our view is that there was some evidence of a degree of protection, but it wasn’t great,” he says. “So we still don’t effectively know if face masks in the community work.”
Hunter thinks there is enough evidence to support mask-wearing for some frontline staff, such as those working in public transport or supermarkets, as well as vulnerable people who temporarily enter high-risk environments like hospitals – as long as their use doesn’t deprive healthcare workers of equipment.
MacIntyre agrees, and says that until more medical masks become available, homemade masks are worth using outside of healthcare settings.
If you are going to make your own mask, there are some important points to remember, says MacIntyre. An effective face mask is one that fits well around the nose, mouth and chin, providing a seal that doesn’t let air in around the sides, she says. It must also filter out particles that could contain the virus.
Vacuum cleaner bags seem to be particularly good at this, according to a 2013 study that compared various household materials based on their ability to filter bacterial and viral aerosols. Tea towels were reasonably effective, but linen and silk performed poorly.
If you do wear a mask, it is important to use it properly. It is easy to contaminate your own mask by touching or reusing it, for example. And don’t let wearing a face mask give you a false sense of security: you can still become infected while wearing one, and washing your hands frequently is vital whether you wear a mask or not.
Even if everyone followed this advice, it isn’t clear whether widespread use of face masks would have a significant impact on the spread of the virus. The WHO says it is “collaborating with research and development partners to better understand the effectiveness and efficiency of non medical masks”. “There’s just not a lot of evidence for cloth masks in the community,” says MacIntyre.
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