A cluster randomised trial of cloth masks compared with medical masks in healthcare workers.
Summary (full text is in the link at the bottom).
Objective The aim of this study was to compare the efficacy of cloth masks to medical masks in hospital healthcare workers (HCWs). The null hypothesis is that there is no difference between medical masks and cloth masks.
Conclusions This study is the first RCT of cloth masks, and the results caution against the use of cloth masks. This is an important finding to inform occupational health and safety. Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection."
TL;DR "Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection."
Full text of the study
https://bmjopen.bmj.com/content/5/4/e006577.full