If face masks really stop Covid, then why are so many of us still catching it?

Stifling. Itchy. Dehumanising. Oppressive. Profoundly un-British. Just some of the terms used to describe the experience of mask-wearing.

Last week, London Mayor Sadiq Khan argued that we should extend the annoyance to outdoors – on our high streets – to protect our fellow Christmas shoppers.

The World Health Organisation (WHO) is urging us to wear face masks around the Christmas table.

But is all this face-mask-wearing helping? Surveys show that three-quarters of Britons are wearing masks in mandatory areas – public transport, offices, pubs and restaurants when not sitting at a table, and most indoor spaces.

Yet the infection is still spreading at a rate that requires 38 million Britons to be banned from mixing indoors with anyone outside of their household.

Last week, cases increased in every area of England bar Yorkshire and the Humber, and in some areas the infection rate leapt up to twice what it was in April.

So are they useless, after all? If Mr Khan’s logic is to be believed, perhaps the problem is that we aren’t wearing them outdoors – surrounded by crowds of people. But studies show that just one in 100 cases is transmitted outside.

Nations that did implement mandatory mask-wearing outdoors, such as Spain and Italy, haven’t been spared devastating further waves.

Indoors, the theory is that masks trap the viral particles that are expelled from an infected person’s mouth or nose when they cough, splutter, sneeze or talk.

Professor Paul Digard, a virologist at the University of Edinburgh explains: ‘A major source of transmission is through liquid droplets – like coughs and sneezes – which send the virus flying through the air.

‘Covid particles are too tiny to be stopped by a mask...'

In July, the WHO published new guidance regarding viral spread via smaller, lightweight particles that travel through the air – like smoke or dust – and linger long after the infected person has left the area.

‘Masks can do little to stop airborne transmission,’ says Prof Digard. ‘Covid particles that aren’t contained in water droplets are too small to be stopped by them.’

One study on their effectiveness, involving 6,000 participants wearing surgical masks at all times while out in public, proved inconclusive. 

As for whether they stop the virus getting in, protecting the wearer, the evidence is even more flimsy.

‘Masks are unlikely to stop you catching the virus but they’re much more likely to trap infected water droplets coming out of your mouth,’ says Prof Digard.