I have not checked any of these links recently but this was the scientific study info on masks I had been collecting last year.
Why Face Masks Don’t Work: A Revealing Review
October 18, 2016
by John Hardie, BDS, MSc, PhD, FRCDC
https://www.oralhealthgroup.com/features/face-masks-dont-work-revealing-review/
Controversy: Respiratory Protection for Healthcare Workers
Kathleen H. Harriman, PhD, MPH, RN; Lisa M. Brosseau, ScD
April 28, 2011
https://www.medscape.com/viewarticle/741245_print
Blaylock: Face Masks Pose Serious Risks To The Healthy
https://www.technocracy.news/blaylock-face-masks-pose-serious-risks-to-the-healthy/
New England
https://www.nejm.org/doi/full/10.1056/NEJMp2006372
A Study on Infectivity of Asymptomatic SARS-CoV-2 Carriers
https://pubmed.ncbi.nlm.nih.gov/32513410/
OSHA oxygen level interpretation
https://www.osha.gov/laws-regs/standardinterpretations/2007-04-02-0
CDC guidance for H1N1
https://www.cdc.gov/h1n1flu/masks.htm
The confirmed effectiveness of medical masks is crucially important for lower-resource and emergency settings lacking access to N95 respirators. In such cases, single-use medical masks are preferable to cloth masks, for which there is no evidence of protection and which might facilitate transmission of pathogens when used repeatedly without adequate sterilization [8].
We found no clear benefit of either medical masks or N95 respirators against pH1N1. However, current policies mandating standard and droplet precautions when performing routine care for influenza patients are reasonable. RCTs conducted in community settings have demonstrated protective effects of medical masks in combination with hand-hygiene and other infection control interventions
https://academic.oup.com/cid/article/65/11/1934/4068747
Flu virus is about 1000 times smaller than the width of a human hair. This study looks at the pore sizes of 20 different cotton masks versus N-95 surgical masks.
The researchers found that all of the cotton masks had pore sizes that were bigger than the width of a human hair – and got even bigger after washing. This means that the width of the holes in every cotton mask are 1000 times bigger than the size of the corona virus. Like trying to catch a fish with a net where the holes were 1000 times bigger than the fish you were trying to catch. surgical masks might stop bacteria – which are ten times bigger than viruses.
https://www.ncbi.nlm.nih.gov/pubmed/31289698
https://aapsonline.org/mask-facts/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7680614/