The consensus seems to be that you should wear a mask not to protect yourself from the virus, but to prevent spread in case you're carrying it and have no symptoms. If everyone wears a mask, contagion is dramatically reduced.

I think the parent was asking for sources.

It seems to be well researched and documented by now that masks are quite effecting in reducing transmissions

https://science.sciencemag.org/content/368/6498/1422.full

The paper doesn't actually say that. It says nobody really knows basic things you'd need to determine that, for example:

Given how little is known about the production and airborne behavior of infectious respiratory droplets, it is difficult to define a safe distance for social distancing

There are plenty of scientists saying masks have no effect when worn by people who aren't actually both visibly sick and working in healthcare:

https://www.cidrap.umn.edu/news-perspective/2020/04/commenta...

In fact manufacturers of ear loop/cloth masks specifically say they can't stop COVID:

https://off-guardian.org/wp-content/medialibrary/EYZu2Q2X0AA...

The WHO said:

https://www.foxnews.com/world/who-guidance-healthy-people-we...

"If you do not have any respiratory symptoms such as fever, cough or runny nose, you do not need to wear a mask," Dr. April Baller, a public health specialist for the WHO, says in a video on the world health body's website posted in March. "Masks should only be used by health care workers, caretakers or by people who are sick with symptoms of fever and cough."

There's plenty of contradictory research out there. Maybe a mask helps if you're literally coughing up phlegm all over the place, but COVID has a dry cough and obviously symptomatic people don't seem to be the only way it spreads.

And fortunately, it's easy to understand the mechanism of action that explains the positive impact of masks: the primary means of covid spread is virus conveyed not individually but in large water droplets. Any filter that impedes the flow of these droplets is very likely to diminish the spread of the contagion. Therefore, anyone who is physically within the field of oral spray of an infected person should benefit from BOTH parties wearing masks.

If all scientific explanations also came with strong and plausible proposals of causation, science-based advice would be much harder to dismiss, whether that dismissal is motivated by mechanism-free (and evidence-free) theories like tribalism or not.

This is a good source. I'm baffled by people still asking for "evidence" of mask effectiveness despite tons of proof for it.

Something tells me this comes from people who cannot be satisfied with rational/scientific proof anyway.

The use of mask has been so prevalent, its mechanism so very simple and intuitive, its down-side so little, that I think in this case, the burden of proof is on the other side. Unless scientists find evidence that proves the masks to be useless or harmful, I'll continue to wear mask when I absolutely need to go out.

First answer from Google:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7191274/

The research includes cloth masks, medical masks, and respirators in community and medical settings.

Conclusion:

“ The study suggests that community mask use by well people could be beneficial, particularly for COVID-19, where transmission may be pre-symptomatic. The studies of masks as source control also suggest a benefit, and may be important during the COVID-19 pandemic in universal community face mask use as well as in health care settings. Trials in healthcare workers support the use of respirators continuously during a shift. This may prevent health worker infections and deaths from COVID-19, as aerosolisation in the hospital setting has been documented.”

Anecdotal evidence: Flushing, Elmhurst, and Jackson Heights are 3 densely populated working-class immigrant neighborhoods in Queens, NYC. In my personal observation, in Flushing (which has a large Chinese population) average people on the street and in grocery stores started wearing masks since February. In Elmhurst and Jackson Heights (large Latin American and South Asian populations) there were no masks in sight until maybe April.

The rate of Covid infection in Elmhurst and Jackson Heights is ~50% higher than in Flushing.

This recent Axios article has some pointers:

https://www.axios.com/coronavirus-face-mask-science-e9df446b...

(BTW, why the downvotes for the original poster? He is not advocating not wearing masks, just expressing his personal unease with them, and asking for evidence. FWIW, I also don't like them, and nevertheless think one should wear them (like condoms)).

EDIT to add: Some direct links (from the article)

https://www.thelancet.com/journals/lancet/article/PIIS0140-6...

https://www.healthaffairs.org/doi/pdf/10.1377/hlthaff.2020.0...

https://www.researchgate.net/publication/342198360_Associati...

https://www.buzzfeednews.com/article/peteraldhous/mario-moli...

It always baffled me how people keep demanding "evidence" for the benefits of wearing masks when even a simple observation provides it.

There's plenty of videos of experiments you can conduct yourself (like the the aerosol ones or just people trying to blow out a candle) showing how masks stop spreading the virus.

Also, have a look at you own monitor screen. See all the funny, dirty dots? That's your spit. Does that compute now?

https://twitter.com/TheLancet/status/1267585465424719873 for a link to a meta-analysis

This article was the most convincing for me http://archive.is/QHU1H

Others included sources, but also, how could masks not be effective? They cover your mouth and the disease is mainly expelled out your mouth. That’s why the government really lost the public when they said “masks don’t do anything” when what they really meant is “there is a mask shortage and America doesn’t have the civic fabric for people to leave masks for the more vulnerable — instead they will start hoarding.”

Similar is the pretense that the race protests wouldn’t explode the transmission of COVID — how could they not?

> Similar is the pretense that the race protests wouldn’t explode the transmission of COVID — how could they not?

Well, so far its looking like they did not. There seem to be three reasons:

1. High rate of mask wearing,

2. They were outdoor events where people were moving about a great deal, and

3. Only 1-2% of the attendees were infected.

You need to get a certain amount of a given virus to actually get infected. For most respiratory viruses if you are just briefly near an infected person and they do not do something to emit a large number of viruses at one (such as cough or sneeze right near you) you won't get enough viruses from them to become infected.

Here's an article about this for the Minnesota protests [1].

[1] https://www.wired.com/story/what-minnesotas-protests-are-rev...

This is absolutely false. Exposure to a higher number of viruses might increase probably of an infection, but a single virus can certainly lead to a full blown infection in an individual.

There seems to be some evidence that a higher infectious dose will not only increase the probability of an infection, but also its severity.

(This makes sense in a simple thought model where the virus starts replicating once it "hits" you, and then your immune system needs N days to ramp up and attack it back. The bigger the initial load, the more the immune system will have to fight back once it's operational. - Not saying that's how it is, just that this is a simple model to make plausible what appears to be empirically seen.)

The infectious dose for most viruses is higher than that. See [1] and [2].

[1] https://www.erinbromage.com/post/the-risks-know-them-avoid-t...

[2] https://en.wikipedia.org/wiki/Minimal_infective_dose

It's a probabilistic process. 1 virion of any virus can infect a host, but for some viruses that probability will be vanishingly small while in others it will just be regular small.

In section 7 of the elsewhere-mentioned http://archive.is/QHU1H , Scott Alexander concludes (with explanations) that the initial policy of not recommending masks was not a deliberate attempt to prevent hoarding. Note that, in coming to this conclusion, he reversed his initial opinion on the matter.

And while there is little doubt that maskless protests of any sort cause spreading, there is little evidence so far of them causing the transmision to "explode".

But Fauci himself straight out admitted that was the intention, did he not?

Hm... apparently so, though in the only example I have found so far, he offers that reason as a justification for declining to recommend masks for people not at special risk. IMHO, this is was a valid response at the time, and not a hidden agenda.