Masks and face coverings for the lay public: A narrative update

Whether and when to mandate the wearing of masks or face coverings by the public to prevent the spread of Covid-19 remains controversial. We summarise a large research literature across a range of academic disciplines. There is growing evidence that SARS-CoV-2 is airborne, hence may travel long distances and be inhaled. Infection control policies must therefore go beyond contact and droplet measures (such as hand-washing and cleaning surfaces) and attend more carefully to masking and ventilation. Masks work mainly by source control (protecting others) but give some protection to wearers. Even small reductions in individual transmission with ‘imperfect’ masks and face coverings could lead to large effects on population spread. Randomized controlled trials of the preventive effect of population masking in Covid-19 remain sparse and have not addressed source control. Performance varies widely across different kinds of mask; comfort and fit need to be optimized. Masks may cause discomfort and communication difficulties, which affect some groups (e.g. d/Deaf) disproportionately. The harms of mask-wearing were over-estimated in the early months of the pandemic; there is no evidence that risk compensation occurs in people who wear them or that masks account for significant fomite transmission. Masks do not cause clinically significant physiological decompensation in healthy people. Documented medical exemptions to mask-wearing are few. The psychological impacts of masks are culturally shaped; they may include threats to autonomy, social relatedness and competence. Whilst harms of masks are generally outweighed by benefits when COVID-19 is spreading in a population, mandated masking involves a trade-off with personal freedom, so such policies should be pursued only if the threat is severe and benefits cannot be achieved through less intrusive means.