Beltran, D. G., Isch, C., Ayers, J. D., Alcock, J., Brinkworth, J. F., Cronk, L., Hurmuz-Sklias, H., Tidball, K. G., Horn, A. V., Todd, P. M., & Aktipis, A. (2021). Mask wearing behavior across routine and leisure activities during COVID-19. PsyArXiv. https://doi.org/10.31234/osf.io/2qya8

Stajduhar, A., Ganel, T., Avidan, G., Rosenbaum, R. S., & Freud, E. (2021). Face Masks Disrupt Holistic Processing and Face Perception in School-Age Children. PsyArXiv. https://doi.org/10.31234/osf.io/fygjq

Ingram, G., Chuquichambi, E. G., Jimenez-Leal, W., & Olivera-LaRosa, A. (2021). In Masks we Trust: Explicit and Implicit Reactions to Masked Faces Vary by Voting Intention. PsyArXiv. https://doi.org/10.31234/osf.io/9d4eu

Covid One Year Ago. (2021, March 12). 12 March 2020 “The public could be putting themselves more at risk from contracting coronavirus by wearing face masks.” “Jenny Harries, England’s deputy chief medical officer, said the masks could ‘actually trap the virus’ and cause the person wearing it to breathe it in” https://t.co/ar5kOOxih3 [Tweet]. @YearCovid. https://twitter.com/YearCovid/status/1370307577888698369

Face masks could increase risk of getting coronavirus, medical chief warns. (2020, March 12). The Independent. https://www.independent.co.uk/news/health/coronavirus-news-face-masks-increase-risk-infection-doctor-jenny-harries-a9396811.html

ReconfigBehSci {@SciBeh}. {2021-03-04] there will be many a wrong analysis as we cycle through the 1 year anniversary and there is nothing to mark this one out as uniquely bad, but what does seem surprising to me in hindsight is the confidence with which people pronounced given that this was a new disease.[Tweet}, Twitter. Retrieved from: twitter.com/SciBeh/status/1367531205198049285

Grover, Natalie. ‘Should Primary Schoolchildren Be Made to Wear Masks?’ The Guardian, 2 March 2021, sec. Education. https://www.theguardian.com/education/2021/mar/02/should-primary-schoolchildren-be-made-to-wear-masks.

WearingisCaring {@WearingisCaring} (2020) How can you safely take off your mask? Simply follow these four easy steps to prevent catching the virus! Twitter. Retrieved from: https://twitter.com/WearingisCaring/status/1295707116880134145

Take away: Though not a guarantee of health, wearing masks reduces the number of respiratory infections compared to no/inconsistent mask wearing.

The claim: Masks are protective against clinical respiratory illness.

The evidence: The authors performed a meta-analysis of random controlled trials and observational studies examining mask use in health care workers. The results showed that wearing masks resulted in fewer infections compared to people without masks. These results agree with other publications (1, 2). One pre-print article which performed meta-analysis showed inconclusive results concerning the effectiveness of masks (3). Based on these meta-analyses, mask wearing results in fewer respiratory infections, though it will not prevent all infections when used as the sole protective measure.

Sources:

1) https://pubmed.ncbi.nlm.nih.gov/32497510/

2) https://pubmed.ncbi.nlm.nih.gov/27632416/

3) https://www.medrxiv.org/content/10.1101/2020.03.30.20047217v2

Gandhi. M., Beyer. C., Goosby. E., (2020). Masks Do More Than Protect Others During COVID-19: Reducing the Inoculum of SARS-CoV-2 to Protect the Wearer. SpringerLink. Retrieved from: https://link.springer.com/article/10.1007/s11606-020-06067-8

Liebst, Lasse Suonperä, and Marie Rosenkrantz Lindegaard. ‘Face-Touching as a Possible Correlate of Mask-Wearing: A Video Observational Study of Public Place Behavior during the COVID-19 Pandemic’. Preprint. PsyArXiv, 22 August 2020. https://doi.org/10.31234/osf.io/u6wcp.

‘Coronavirus Cases Surge as France Goes “Wrong Way”’. BBC News, 11 August 2020, sec. Europe. https://www.bbc.com/news/world-europe-53745481.

AP NEWS. ‘Health Officials Are Quitting or Getting Fired amid Outbreak’, 10 August 2020. https://apnews.com/8ea3b3669bccf8a637b81f8261f1cd78.

It sounds like it's recommended because a significant portion of people with coronavirus are asymptomatic or pre-symptomatic, and the virus can spread through speaking, coughing or sneezing.

There's no "proof" that these work, but there's a hope that it helps along with hand washing and a distance of six feet.