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BackgroundThe Ministry of Social Affairs and Health in Finland commissioned this systematic literature review on the effectiveness and safety of using face masks in public environments in protecting against upper respiratory tract infections, to inform policy. Previous reviews have not clearly distinguished the context of mask use.MethodsThe review was completed within two weeks, adhering to the PRISMA guidelines where possible. The review looks at the effect of face coverings (surgical masks or cloth coverings, excluding FFP2 and FFP3 masks) in protecting against the transmission in droplet-mediated respiratory tract infections. Our review includes controlled trials or previous systematic reviews of mask use by the general public in public spaces, outside homes and healthcare facilities.ResultsThe systematic literature search identified five randomized trials. Use of masks prevented infections in one subgroup of one pilot study, so the effect of face masks on the transmission of infections outside the home appears small or nonexistent. Five of the eight systematic reviews showed no evidence of face masks being helpful in controlling the spread of respiratory infection or preventing exposure in healthy individuals. Meta-analyses often combined very heterogeneous studies and costs were not reported in any studies.ConclusionsRandomized studies on the effect of face coverings in the general population are few. The reported effect of masks used outside the home on transmission of droplet-mediated respiratory infections in the population is minimal or non-existent. It is difficult to distinguish the potential effect of masks from the effects of other protective measures.Summary boxWhat is already known on this subject?Previous reviews on the effectiveness and safety of use of face masks in protecting against upper respiratory tract infections have not clearly distinguished the context of mask use. They have combined very heterogeneous studies done in homes, health care settings, or public environments.What does this study add?Our systematic review on the use of face masks in public environments, done to inform an impending policy decision, found five randomized trials (RCTs) and eight reviews. Use of masks prevented infections in one subgroup of one RCT, so the effect of face masks appears small or nonexistent.