Contents A) Studies ⇓ B) WHO review ⇓ C) Real-world evidence ⇓ D) N95/FFP2 masks ⇓ E) Additional aspects ⇓ F) The aerosol issue ⇓ G) Contrary evidence ⇓ H) Mask-related risks ⇓ I) Conclusion ⇓ A) Studies on the effectiveness of face masks So far, most studies found little to no evidence for the effectiveness of face masks in the general population, neither as personal protective equipment nor as a source control. A May 2020 meta-study on pandemic influenza published by the US CDC found that face masks had no effect, neither as personal protective equipment nor as a source control. (Source) A WHO review of ten randomized controlled trials of face masks against influenza-like illness, published in September 2019, found no statistically significant benefit. (Source) A Danish randomized controlled trial with 6000 participants, published in the Annals of Internal Medicine in November 2020, found no statistically significant effect of high-quality medical face masks against SARS-CoV-2 infection in a community setting. (Source) A large randomized controlled trial with close to 8000 participants, published in October 2020 in PLOS One, found that face masks “did not seem to be effective against laboratory-confirmed viral respiratory infections nor against clinical respiratory infection.” (Source) A February 2021 review by the European CDC found no high-quality evidence in favor of face masks and recommended their use only based on the ‘precautionary principle’. (Source) A July 2020 review by the Oxford Centre for Evidence-Based Medicine found that there is no evidence for the effectiveness of face masks against virus infection or transmission. (Source) A November 2020 Cochrane review found that face masks did not reduce influenza-like illness (ILI) cases, neither in the general population nor in health care workers. (Source) An August 2021 study published in the Int. Research Journal of Public Health found “no association between mask mandates or use and reduced COVID-19 spread in US states.” (Source) A July 2021 experimental study published by the American Institute of Physics found that face masks reduced indoor aerosols by at most 12% and even increased them locally. (Source) An article in the New England Journal of Medicine from May 2020 came to the conclusion that face masks offer little to no protection in everyday life. (Source) A 2015 study in the British Medical Journal BMJ Open found that cloth masks were penetrated by 97% of particles and may increase infection risk by retaining moisture or repeated use. (Source) An August 2020 review by a German professor in virology, epidemiology and hygiene found that there is no evidence for the effectiveness of face masks and that the improper daily use of masks by the public may in fact lead to an increase in infections. (Source) For a review of studies claiming face masks are effective, see section G) below. More details and source links at above link.