Since the beginning of 2020 the SARS-CoV-2 virus has spread to nearly every country in the world. The mainly airborne pathogen has led to large numbers of deaths, principally in elderly and vulnerable segments of the population. Protective vaccines have recently become available, but it is not yet clear whether and when population-wide immunity will be achieved. The existence of evidence for the protective effect of masks covering the mouth and nose is a topic of public debate.
A selective literature search was carried out in PubMed. Data from the German Robert Koch Institute and the Centers for Disease Control and Prevention were also taken into account.
When talking, as many as 20 000 droplets ranging in size from 20 to 500 μM are released every second. According to PCR tests, the amount of virus exhaled is highest immediately before the onset of symptoms. No randomized trials have been conducted on the effect of masks covering the mouth and nose. A metaanalysis of 29 studies on infection with SARS-CoV-2, SARS, or MERS revealed that type N-95 masks (corresponding approximately to FFP-2), surgical masks, or similar multilayer cotton masks can greatly reduce the infection risk for the wearers (RR 0.34 [0.26; 0.45], with moderate heterogeneity [I2 = 48%]). Model experiments and case reports suggest that masks covering the mouth and nose afford considerable protection against transmission of SARS-CoV-2 and other airborne diseases by reducing release of and exposure to potentially infectious droplets; in addition, infections that do occur take a milder course. A limitation of the studies analyzed is that in most cases, this effect cannot be viewed in isolation from the protective impact of other measures (distancing, hygiene precautions).
It can plausibly be assumed that consistent use of masks covering the mouth and nose can play an important role in containing the spread of SARSCoV- 2.

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