Thread by @trishgreenhalgh

MASKS are back (=> they’re trending on social media and I’m getting hate mail). A short thread. See my pinned tweet for a longer thread with lots of peer-reviewed articles.🧵
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Masking is a deeply symbolic practice. In some social groups, a mask is a muzzle, a ‘face diaper’ or a sign that you’ve given in to state control. Criminals, pirates, political protesters and others with something to hide wear masks. Masked people are suspicious.
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In other social groups, masking during a pandemic means that you care about the common good. My mask protects ME from inhaling airborne virus—and it also protects YOU because I may be infected but not know it. Even if I’m healthy, others may be vulnerable.
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The science of masks is NOT complex, nor is it conflicting. Science shows very clearly that masking is effective in reducing transmission of SARS-CoV-2. This has been shown in laboratory studies, natural experiments, modelling studies and randomised controlled trials (RCTs).
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The scientific controversy relates to three issues. First, experiments such as RCTs cannot ever detect the full impact of masking, because they only evaluate whether the person wearing the mask (or the person in the no-mask control group) becomes infected.
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RCTs of mask v no-mask can't evaluate the MAIN impact of masking, which is to protect *other people* from the mask-wearer’s germs. And they can’t evaluate how a small (“not statistically significant”) reduction in transmission gets magnified over time.

https://twitter.com/trishgreenhalgh/status/1414296107262246917?s=20&t=-C9x-EpAw0FjCFTjuz-ndw

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The second controversy is that masking is inconvenient, uncomfortable, interferes with communication (especially if deaf), and may cause claustrophobia. This is why we should only mandate masking when the BENEFITS outweigh the DOWNSIDES.
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But just because masking has a downside doesn’t mean it’s NEVER a good idea. We need to weigh the trade-offs. Masking (perhaps for most but not all adults and older teens) is worthwhile *when covid rates are high* and when *vulnerable people* are around (e.g. in hospitals).
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The third controversy is whether the untrained lay public is ever going to be able to mask up effectively (as opposed to on their chin or with their nose popping out). But this is not an argument that masks don’t work—it’s an argument for *better public education*.
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In sum, evidence for masking is strong, consistent and clear. A high-quality, well-fitting mask which meets a filtration standard (e.g. FFP2 or N95) works better than a home-made cloth mask with gaps round the sides, but even the latter is a lot better than nothing.
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Where is this evidence? Work your way through this 100+-tweet thread which I began in July 2021 and have updated since. It appears to stop at tweet 31 (bug) but look for replies to that and you’ll see tweet 32 and pick it up again.

https://twitter.com/trishgreenhalgh/status/1414294003479089154?s=20&t=-C9x-EpAw0FjCFTjuz-ndw

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Why do some scientists insist that there is “no evidence” for masks? Primarily, I think, because their libertarian identity prompts them to a) frame masking as a coercive & suspicious activity and b) focus narrowly on benefits to the wearer rather than to society as a whole.
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Why are so many anti-vaxers also anti-masks? Again I think it’s linked to libertarian identity. But libertarian views about what *should* be the case (e.g. whether masking should be mandated) can’t change what *is* the case (e.g. the science of whether masking is effective).
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Why do anti-maskers spend so long on their keyboards writing ad hominem tweets about what a rubbish scientist I am (also my bad hair, putative sexual orientation etc) and telling me to go f**k myself? Because if they engaged with the actual science they’d be lost for words.
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Bottom line: covid rates are sky-high. Nasty flu is also circulating. Hundreds are dying every week of preventable respiratory infections. Hospitals are full. Primary care is collapsing. It could be you or your relative on that 30-hour trolly wait. So WEAR A MASK!
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