One of the most politicised scientific issues of 2020 was the question about whether face-masks stop the spread of COVID-19. I trust we can agree that this is notable without requiring specific examples.

In particular:

When worn by members of the public who are healthy, are cloth facemasks effective at slowing the spread of COVID-19?

Cloth facemasks refer to the non-disposable, often hand-crafted, masks that have been widely adopted, often in response to government mandates. Their quality may vary; if your evidence is focused on particular specifications (number of layers, material, age, etc.) please make that clear.

Note that this question is about effectiveness (not efficacy), so answerers and voters are invited to weight evidence about the spread of COVID-19 in real-life conditions above evidence from lab experiments, and in turn, evidence from lab-experiments above theoretical models.

This question is one of a number of similar questions on Skeptics.SE. For a master list, see here

  • An interesting point, not about Covid but about Rhinovirus... Washing your cloth mask on your own can double your risk of infection. blogs.bmj.com/bmj/2020/09/29/… You can probably see why this is such pain to study... Jan 4, 2021 at 20:56
  • 3
    @Fizz: My reaction "Nah, can't be true... reads OH! Handwashing in a hospital basin! Oh no!"
    – Oddthinking
    Jan 4, 2021 at 21:47
  • 2
    Why are you asking specifically about healthy subjects? Masks are supposed to be worn by all so that when people are infected and infectious but not yet symptomatic, they do not unknowingly infect others.
    – Ivana
    Feb 10, 2022 at 13:18
  • @Ivana: Because people made this claim. See the master list referenced.
    – Oddthinking
    Feb 10, 2022 at 14:16
  • 1
    Is it only I or are the questions in the title and in the post completely different?
    – Haukinger
    Sep 27, 2022 at 8:50


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