Intended for healthcare professionals

Letters Face masks for the public during covid-19

Covid-19: are face masks a good long term strategy?

BMJ 2020; 369 doi: (Published 20 May 2020) Cite this as: BMJ 2020;369:m2005
  1. Sheung-Tak Cheng, university professor
  1. Department of Health and Physical Education, Education University of Hong Kong, 10 Lo Ping Road, Tai Po, New Territories, Hong Kong
  1. takcheng{at}

Greenhalgh and colleagues1 and Javid and colleagues2 argue for public use of face masks or coverings. Despite known problems with compliance in flu seasons, the authors suggest that people might be more motivated to wear masks to avoid the more deadly SARS-CoV-2. Nevertheless, a factor contributing to non-adherence is “mask fatigue.” Most people (including some health professionals3) cannot tolerate wearing a mask all day; others can but quickly develop resistance to using it further.

Another question is whether to advise mask wearing at home given the preponderance of familial transmission,45 especially for those living in crowded households or with people at risk (such as older relatives). We don’t yet know how to make good use of masks so that they are worn when needed most without leading to fatigue.

A common argument for masks is to prevent transmission from pre-symptomatic people. Notably, however, the efficacy of surgical masks in filtering SARS-CoV-2 is questioned in a preliminary study of patients with covid-19 coughing with or without masks.6 We also don’t know whether asking both infected and uninfected parties to wear masks is advantageous. A recent review indicates that the benefit might be limited to high risk settings (clinics and hospitals);7 these studies were done in Asia where both parties wearing masks is the norm.

The Singapore experience indicates that the virus might not burn out in hot weather. But keeping masks on is harder in summer, which is not too far from now. Moreover, the moisture from sweat might render the mask ineffective and create a favourable habitat for the virus.8 Thus, the utility of mask wearing is probably limited in the current outbreak, but promoting it now might increase readiness to adopt it should another outbreak occur in autumn or winter. Meanwhile, we need more research about the efficacy of mask wearing in cutting transmission to inform policy in the next outbreak.


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