Why should we all wear face masks?

From your link:

> (eg, reusable 12–16-layer cotton masks; pinteraction=0·090; posterior probability >95%, low certainty

That "low certainty" comes from GRADE. Low certainty in GRADE means "The true effect might be markedly different from the estimated effect". Masks may be very much better, or very much worse, than they estimate.

The Interpretation section says this:

> Robust randomised trials are needed to better inform the evidence for these interventions, but this systematic appraisal of currently best available evidence might inform interim guidance.

Which suggests to me that they want more and better evidence.

The end of the paper says this:

> Our comprehensive systematic review provides the best available information on three simple and common interventions to combat the immediate threat of COVID-19, while new evidence on pharmacological treatments, vaccines, and other personal protective strategies is being generated. Physical distancing of at least 1 m is strongly associated with protection, but distances of up to 2 m might be more effective. Although direct evidence is limited, the optimum use of face masks, in particular N95 or similar respirators in health-care settings and 12–16-layer cotton or surgical masks in the community, could depend on contextual factors; action is needed at all levels to address the paucity of better evidence. Eye protection might provide additional benefits. Globally collaborative and well conducted studies, including randomised trials, of different personal protective strategies are needed regardless of the challenges, but this systematic appraisal of currently best available evidence could be considered to inform interim guidance.

These sentences make me think the evidence isn't as strong as lots of people claim it is:

> while new evidence on [...] other personal protective strategies is being generated.

> Although direct evidence is limited

> action is needed at all levels to address the paucity of better evidence.

It really bothers me that a medical device has become something so political and so disconnected from evidence-based science that I need to say this, but: for what it's worth, I wear a mask when near other people, both because they may be effective, and because the people I'm near may believe that they are and may thus feel safer seeing me wear it. I can feel that the evidence is very weak and yet still do that.

As such, any environmental effect: heat, dryness, humidity, UV-light, or chemicals, will kill the virus extremely quickly.

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With that being said: E. Coli can still grow on a mask, and I would recommend proper sanitation of your masks. A "standard" bacterial infection would still suck, even if it isn't COVID19.

So even IF COVID19 dies in minutes to sunlight (a fact that I find plausible, given the very low levels of protections viruses have vs the environment), its a bad idea to aim at "only disinfecting COVID19". There's many fungus, bacteria, AND viruses that can get stuck on a mask.

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Hydrogen Peroxide has been shown to be a strong anti-viral, anti-bacterial, and anti-fungal agent. Or, toasting your N95 masks in ~180F ovens for 30 minutes also would do the trick. (Again: the higher temperature and time is NOT for the easily killed virus, but for the harder to kill bacteria and fungus)

I know that aerosolized H2O2 has been used to recycle / reuse masks in hospitals. I don't know if liquid H2O2 is safe for masks. So I guess the oven-toast methodology is the best I've heard so far.

Aerosol H2O2 is toxic however. And unfortunately, I don't recall the percentage that they used for the study (3% is common household grade. But hospitals are known to use 7% or 10% grade for disinfection purposes). H2O2 is also highly reactive, so its possible it damages the mask somehow. But as a cleaning agent, its both cheap and effective (as long as the base material can survive).

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For your cloth masks: your standard laundry detergent is a good anti-fungal, anti-bacterial, anti-viral soap. The issue with N95 masks is that they can't survive the laundry or other, more rigorous forms of cleaning. Throw some chlorine bleach into the wash if you want to be extra sure (a 2nd, independent anti-fungal, anti-bacterial, anti-viral chemical for good measure).

EDIT: Can someone please explain the downvotes? We have a classic A/B question here. We should NOT only be aiming to kill viruses (which is extremely easy). If we want to protect ourselves while using masks, we should aim at killing viruses, bacteria, AND fungus. That is, all the different micro-organisms that can be found on a mask.

It says that "Based on their results, the researchers estimate that continuous exposure to far-UVC light at the current regulatory limit would kill 90% of airborne viruses in about 8 minutes, 95% in about 11 minutes, 99% in about 16 minutes, and 99.9% in about 25 minutes."

I don't know how the "regulatory limit" compares to sunlight. Also, this is for seasonal coronaviruses rather than specifically SARS-CoV-2, and it's for airborne particles rather than masks. Maybe someone can find something more specific?