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Wearing masks in crowded indoor spaces appears to have worked a bit too well for me: Never had as much as a sniffle during the pandemic, despite traveling more than usual. But as soon as I stopped wearing masks, I get sick 3 times within 4 months... Pre-pandemic, the only times I remember coming down with a full-blown cold was after long-distance flights (jetlag + lots of exposure?). So I'll keep wearing masks in airport terminals and when getting on or off airplanes.

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Personal science is about whatever works for you, so I'm glad you found something.

Incidentally, the evidence for Vitamin D is at least as good as masks. I always wonder why that doesn't get more attention.

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Evidence for supplementing with vitamin D *when deficiency symptoms are present* appears to be quite good. But beyond that there are some correlation-vs-causation questions... Perhaps a better example would be how well *telling* people to improve their diet in specific ways results in measurable improvements...

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I am not clear what is being said about the efficacy of masks. I have read a couple of articles recently. You might want to look up Don Milton's work at University of Maryland, College Park. I don't have a position because I don't know.

A small anecdote. I painted my kitchen cabinets and did some sanding with the doors off. Every opening had brown paper taped to cover the opening and many areas had plastic draped over it. Dust still got everywhere. Not a lot, but it still got everywhere.

One more thought. Physics is important. Many people reason about masks and viruses with the trying to "pickup sand with a tennis racket" model. But other forces are at play resulting from boundary conditions. To understand what I mean, think about how you light a match outside on windy day. You light it near a hard boundary because the wind speed there is zero. Masks do the same thing. So they can deflect a current of virus containing air even if they are porous.

My overall view is that stuff gets in with a typical mask but the goal is not to stop it but to lower it as much as possible: filtering some, deflection to even out density inhomogeneities. If there is a high average density, I don't think a mask will do much.

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Thanks, good point. The Cochrane people didn't say "masks don't work" -- they said "there's no proof that masks work". Still, whatever the effect, it's pretty minuscule.

Re: physics, remember it's possible it goes the other way. Maybe the virus needs some combination of surface (to slow it down) and air ... I could imagine many other possible ways a mask might actually hurt. But the only way to tell is to run an RCT, which the Cochrane people studied as carefully and objectively as I'll ever do, and couldn't find anything.

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