How do face masks prevent the spread of COVID-19?


On the 13th of July, Boris Johnson announced that face coverings will be mandatory in shops in England from the 24th of July in order to limit the spread of coronavirus (COVID-19). This has been a requirement in shops in Scotland since the 10th of July and has been compulsory on public transport in England, Scotland, and Wales since as early as the 15th of June. In Northern Ireland, masks are also compulsory on public transport, with circumstances in indoor spaces being considered and ‘under review’. 

So how do face masks prevent the spread of COVID-19? COVID-19 spreads from person to person through infected droplets from coughing, sneezing, and talking. These droplets can then land on the mouths or noses of those nearby or be inhaled, which spreads the virus to them. Even those who are asymptomatic (infected but don’t show any symptoms) or pre-symptomatic (haven’t yet developed symptoms) can spread the virus through droplets without knowing it. Although social distancing methods can help limit the spread, face masks can prevent it in places where social distancing is difficult to maintain- like on public transport or in smaller shops. 

The CDC recommends cloth face coverings in public settings, and microbiologist Dr. Richard Davis took to twitter in a viral thread to demonstrate how face masks can limit the spread. He carried out an experiment where he sneezed, coughed, sang, and talked towards agar plates with and without a mask. Bacterial colonies grew where the droplets landed, and after incubation he found that the mask blocked ‘virtually all of them’, with very few bacterial colonies growing on the agar plates that he had been near whilst wearing a mask. He also demonstrated the effect of distance- when coughing hard for 15 seconds 2 feet, 4 feet, and 6 feet from an agar plate, wearing a mask again blocked almost all of the droplets. He concludes that although this method isn’t generally how you would culture viruses, it does demonstrate the effectiveness of wearing masks to stop the spread of the virus. 

Although cloth face coverings aren’t up to the same standard as medical-grade PPE (which is reserved for healthcare workers and other key workers), they do limit the spread of COVID-19. Instructions have been released on how to make your own face coverings at home (here and here), and social distancing measures should still be maintained wherever possible. 


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