1/ This is quite the paper on masks, published in @BMJ_Open in 2015: a randomized trial (the gold standard, yadda yadda) of 1600 health-care workers showed those wearing masks were 6 times (!) as likely to have flu-like illnesses as those in the control group after 4 weeks...

2/ The conclusion: “This study is the first RCT of cloth masks, and the results caution against the use of cloth masks... moisture retention, reuse of cloth masks, and poor filtration may result in an increased risk of infection.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/">https://www.ncbi.nlm.nih.gov/pmc/artic...

3/ My mask protects you! By getting me too sick to go outside... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/">https://www.ncbi.nlm.nih.gov/pmc/artic...

To be clear: even in the control arm, some workers wore medical masks (though compliance in the control arm was low). But: it is not clear that medical masks helped. Maybe the most stunning number - 97% (!) of cloth masks admitted viral particles...