Should I wear a face mask in public?

Expert advice from a professor in health sciences

Protection: a woman wearing a homemade mask in Brixton. Simple cloth masks stop 95 to 99 per cent of virus-laden droplets

AFP via Getty Images

Lizzie Edmonds @lizzieedmo

24 April 2020

Why is there still so much confusion about face masks?

“Scientists don’t disagree on what the facts are; they disagree on how much weight to place on which facts. There has not been a large, randomised controlled trial during this pandemic. What we do have is a collection of smaller trials, mostly done in milder epidemics, in which the effectiveness of masks seemed to be limited. Some scientists say this means we have no evidence to support a policy of mask wearing. Others say those trials are irrelevant. Basic physics experiments show a double layer of cloth held in front of your face will block 95 per cent of droplets coming out of your mouth and nose. Scientists are disputing how much weight to place on physics versus the absence of trials”.

Why is there now a suggestion that face masks should be mandatory for the public?

“Cloth face masks are efficient (although not perfect) at blocking larger droplets because they get caught in the weave. Cloth masks are much less good at blocking smaller droplets but this doesn’t matter. Medical-grade masks worn by frontline workers are very fine-weave and are designed to stop even tiny particles getting in and infecting the wearer. But if the person doing the coughing is wearing a cloth mask, 95 to 99 per cent of the virus-laden droplets will be stopped — protecting that proportion of others.”

Will wearing masks be made law or become part of an exit from lockdown strategy?

“I suspect so, although personally I would rather see a voluntary policy as in Hong Kong, where 97 per cent of people now wear a face covering when out in public.”

Should I wear a homemade mask or a scarf rather than no protection at all?

“Yes. A scarf or bandana will block most virus-laden droplets. The exact effectiveness depends on the material, but two layers of cotton will block about 95 per cent of droplets, and a waterproof-backed lining will increase that to about 99 per cent.”

What materials can I use to make a mask at home?

“Cotton is good. Fold it and put in a layer to catch droplets, such as kitchen paper, a pantyliner or a coffee filter.”

From Trisha Greenhalgh, professor of primary care health sciences at Oxford University

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