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Should you wear a face mask outdoors? The science is far from clear

Pedestrians wearing face masks in Manchester after tighter local restrictions were introduced - Paul Ellis/AFP
Pedestrians wearing face masks in Manchester after tighter local restrictions were introduced - Paul Ellis/AFP
Coronavirus Article Bar with counter
Coronavirus Article Bar with counter

Is there any point in wearing a face covering outdoors? The Italian government clearly thinks so. A new rule, due to be signed into law on October 7 by prime minister Giuseppe Conte, obliges everybody to cover their face while outside if they are likely to come into contact with somebody from another household. Exceptions have been made for those playing sports, children under six, and those with breathing difficulties.

After a fairly successful summer of controlling the virus, cases in Italy are starting to climb again, with 2,844 reported on Saturday, the highest daily count since April – although the numbers still lag far behind those in Britain, France, and Spain.

It is now mandatory across much of Europe, including the UK, to wear a face mask in most indoor public settings, like shops and public transport. Italy’s outdoor rule would take the principle one step further, giving it one of the strictest anti-virus regimes in the world.

So, will it work? Most scientists believe that face masks do have a noticeable effect on reducing transmission – although some of the evidence is shaky and complex. A meta-analysis published in July by Oxford University’s Leverhulme Centre for Demographic Science found that “cloth face coverings are effective in reducing source virus transmission” – and they protect the wearer, not just those around them, contrary to popular belief.  A study published in the journal Health Affairs, meanwhile, examined the growth of Covid before and after masks were made compulsory in 15 US states, and found that those states in which masks were mandatory did indeed see a slower rate of virus growth, which soon translated into fewer hospital admissions.

That is why government health agencies in virtually every developed country, including Public Health England in the UK and the Centre for Disease Control (CDC) in the US, have recommended their indoor use.

But the picture becomes far less clear when we step outside. Sars-Cov-2 - the virus that causes Covid-19 - is still a relatively new threat, and there has been virtually no research on the efficacy of face masks in outdoor environments. What scientists do know is that transmission of the virus, as with seasonal flu and other coronaviruses, is far less likely in the open air. Direct sunlight does a good job of killing coronavirus particles, and airborne particles are more likely to dissipate in a breezy street or park than in a poorly-ventilated restaurant or train carriage.

Infectious disease specialist Babak Javid, associate professor at the University of California, San Francisco, says most Sars-Cov-2 transmission occurs indoors, and that the Italian outdoor mask policy will only prevent a very small number of cases. “So the question is, how big of an effect would it have,” he says. “I think the biggest impact is that it gives people the confidence to engage in [outdoor] activities. Covid is incredibly serious but it's not the only game in town, and I think we need to avoid lockdown-style [situations] as much as possible. I’m not convinced there’ll be a huge amount of transmission that’s prevented by wearing masks outdoors, but if it gives the green light for more outdoor activities, then that’s a good thing.”

Prof Javid recently moved from Cambridge to the California Bay Area, where face masks are compulsory outdoors if you cross someone’s path. Compliance is very high, he says. “If you're going to wear a mask indoors it's not extra burdensome to wear it outdoors, especially as we're entering autumn and winter.”

His view is supported by Linsey Marr, an engineering professor and aerosol scientist at Virginia Tech University, who told The New York Times: “I think outdoors is so much better than indoors in almost all cases. There’s so much dilution that happens outdoors. As long as you’re staying at least six feet apart, I think the risk is very low.”

Italy, then, seems to be acting out of an abundance of caution - or perhaps it is driven more by psychological concerns. Some experts think that, as well as protecting people from virus particles, the sight of masks might remind people to take other precautions, like hand-washing and social distancing. This may well have contributed to official thinking in Italy, where after months of impressive adherence to social distancing rules, part of the population is experiencing pandemic fatigue, experts believe, with bars and restaurants in cities becoming noticeably more crowded on weekends.

But clinical psychologist Linda Blair is less sure. Whilst outdoor mask-wearing might produce some degree of “copying effect”, she says, it could also lull wearers into a false sense of confidence. “You also become blaze and go much nearer to people, when you might not necessarily have a safe mask.”

Some fear that outdoor mask-wearing would bring its emotional toll, reducing those all-important casual social connections that psychologists say are important for happiness. MIND and other mental health charities warn that some people find it unnerving if they cannot see the facial expressions of others. But again, Blair is sceptical. Contrary to popular belief, she says, humans communicate far more through our body language than our facial expressions, and we would quickly adjust to a situation in which we can only see people’s eyes. “We're quick to adapt, look at what we've done.”

Read more: How to winter-proof your face mask