The positive points about masks seem to be that they work under the right conditions, if they are the right masks. But the right conditions exist only when proper masks are used by professionals who know how to use them correctly.
Association Of American Physicians And Surgeons Sounds Off On Face Masks
Note: A COVID-19 (SARS-CoV-2) particle is 0.125 micrometers (μm); influenza virus size is 0.08 – 0.12 μm; a human hair is about 150 μm.
*1 nm = 0.001 micron; 1000 nm = 1 micron; Micrometer (μm) is the preferred name for micron (an older term)
1 meter is = 1,000,000,000 nm or 1,000,000 microns
Droplets
Virus is transmitted through respiratory droplets produced when an infected person coughs, sneezes or talks. Larger respiratory droplets (>5 μm) remain in the air for only a short time and travel only short distances, generally <1 meter. They fall to the ground quickly. https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30245-9/fulltext
This idea guides the CDC's advice to maintain at least a 6-foot distance.
Virus-laden small (<5 μm) aerosolized droplets can remain in the air for at least 3 hours and travel long distances. https://www.nejm.org/doi/pdf/10.1056/NEJMc2004973?articleTools=true
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“Advice to decision makers on the use of masks for healthy people in community settings
As described above, the wide use of masks by healthy people in the community setting is not supported by current evidence and carries uncertainties and critical risks.”
“Medical masks should be reserved for health care workers. The use of medical masks in the community may create a false sense of security, with neglect of other essential measures, such as hand hygiene practices and physical distancing, and may lead to touching the face under the masks and under the eyes, result in unnecessary costs, and take masks away from those in health care who need them most, especially when masks are in short supply.”
“Masks are effective only when used in combination with frequent hand-cleaning with alcohol-based hand rub or soap and water.”
WHO acknowledges that most people do not use masks properly.