Whether and how to advise cloth mask adoption by the general public

Updated: May 15

Contribution signée Sylvia Wenmackers (KU Leuven)


One possible measure as part of an exit strategy could be the recommendation to the general public to wear cloth masks when going out in public (including work, shops, social visits, and public transport). This note pertains to a trade-off in communication: one needs to convince people of the added value of the measure, without triggering more risky behavior related to other measures (e.g., social distancing). Although the focus here is on masks, this trade-off and the associated communication advice apply more broadly.

Cloth masks as a prophylactic measure for the general public

Given the shortage of medical masks, the relevant question at hand is whether to advise wider adoption of cloth masks. The following Belgian websites provide patterns for such masks and offer additional advice on their usage: in Dutch https://maakjemondmasker.be/, in French https://faitesvotremasquebuccal.be/, and in English https://makefacemasks.com/

Effectiveness is not studied directly (yet), but highly plausible from indirect studies. As far as Greenhalgh et al. (2020) are aware (and they cite an ‘empty review’ to this effect), “there are no randomised trials of masks so far during the COVID-19 pandemic”. Even absent such a study, it is highly likely that masks–which offer a physical barrier–slow down the spread of the epidemic, especially when worn by infected people. Since there is a significant portion of spread due to presymptomatic carriers, implementing this effectively would require mask use by all (except for infants and people with breathing difficulties, and perhaps those who are confirmed to be immune, if it is known that they cannot infect others). Based on a literature review, Howard et al.(2020) recommend public cloth masks wearing, too. In light of the nonlinear relationship between the infectious dose and the probability of infection (and, possibly, the severity of health effects), even relatively small reductions in the viral load due to low-quality masks may still have comparatively large effects. See, e.g., Taleb(2018); see also Huang (2020) and sources cited therein.

Current international policy advice is mixed, but veers towards more general use. Regarding masks for the general public, official advice differs per country. An overview is given by Greenhalgh et al.(2020). For instance, the World Health Organization (WHO) does not recommend use of masks by the general public, except for people who are suspected to have COVID-19, but the US Centres for Disease Control and Prevention (CDC) has started advising for the use of makeshift cloth face covers since April 4th, 2020.

On April 3rd, 2020, the German Academy of Sciences has also advised to wear masks in public: “Mouth and nose protection reduces the transmission of viruses, especially by reducing the infection through respiratory droplets. There is a large number of individuals with undetected COVID-19 infection, who show no symptoms. Wearing a mouth and nose protection in public protects others and reduces the spread of the infection, thus indirectly lowering the risk of becoming infected. To a limited extent, mouth and nose protection also serves directly to protect oneself. Therefore, a gradual relaxation of the restrictions should go hand in hand with the general use of mouth and nose protection. This applies to the entire public space, amongst others in companies, educational institutions, and in local and long-distance public transport. The prerequisite to reach this goal is the nation wide availability of protective masks. Even at present, self-made mouth and nose protection, shawls and scarves should be used to bridge the shortage. These should cover the mouth, nose, chin and the side edges of the face as completely as possible. FFP2/3 masks should continue to be reserved for medical and care sector as well as for special professional groups.

Applying the precautionary principle

The key messages of Greenhalgh et al. (2020) are

  • The precautionary principle states we should sometimes act without definitive evidence, just in case

  • Whether masks will reduce transmission of COVID-19 in the general public is contested

  • Even limited protection could prevent some transmission of COVID-19 and save lives

  • Because COVID-19 is such a serious threat, wearing masks in public should be advised

In their editorial, Javid et al.(2020) summarize the question in their title as “COVID-19: should the public wear face masks?” and summarize the answer as follows: “Yes—population benefits are plausible and harms unlikely” (See also the joint summary by Greenhalgh & Howard, 2020).

Communication about risk alleviation is essential

For most protection measures (such as airbags in cars), it is known that some risk compensation by users occurs, leading to a lower ‘net effect’ (that is the effect due to the measure itself and the adjusted user behaviour). A review of risk compensation is given in Hedlund (2000). To be sure, risk compensation does not always lead to large behavioural effects (e.g., in their review of risk homeostasis studies related to the effect of HPV vaccination on sexual disinhibition, Kasting et al.(2016) found that “None of the studies of sexual behaviors and/or biological outcomes found evidence of riskier behaviors or higher rates of STIs after HPV vaccination.”). In general, Hedlund (2000) writes: “[Risk] compensation is unlikely if any of the four is zero: the measure is invisible, doesn’t affect me, or I have no motivation or no freedom to change my behavior.”

To the best of my knowledge, there has been no specific study to the effects of wearing a mask on risk compensation, but the measure is very visible. So,it seems prudent to communicate the protection a mask offers in an understated way. Since the behavioural adjustment depends on perceived risk, which rarely coincides with objective risk, it may in principle happen that the net effect is negative (applied to our case, this would mean: increasing the spread of COVID-19). So, it seems crucial that, if wearing cloth masks by the general public is introduced as a measure, then it is to be communicated carefully, without overstating its protective effects.

So, there is a difficult balance between 1) convincing people it is a good idea to wear masks in public, while 2) promoting behaving as if they did not wear a mask. Stressing the precautionary principle (following Greenhalgh et al., 2020) might offer an honest way of communicating this. Regarding 1), expertise from communication and media research, marketing, and psychology of nudging is highly relevant. Presenting the intended behaviour as the default, using attractive images of how public places might look like under the new measures (keeping in mind a diverse audience, with respect to parameters, such as age and socioeconomic background) and participation of role models and influencers are crucial.


In light of the cited sources, it seems advisable:

  1. To recommend that cloth masks be worn in public.

  2. To recommend mass production of such masks in garment workshops and meanwhile to encourage private production (in Dutch https://maakjemondmasker.be/, in French https://faitesvotremasquebuccal.be/, and in English https://makefacemasks.com/).

  3. To present the intended behaviour as the default, in an attractive way.

  4. To motivate the measure without overstating the effects (mentioning the precautionary principle) and emphasizing that it protects others.

An early, effective and helpful piece of advice that circulated during this pandemic was to act as if one had already been infected. Later, as more evidence accumulated regarding the role of spreading the infection by presymptomatic carriers, this seemed even more appropriate. The same type of message can be applied to masks, too: wear a mask as if you were infected, to protect the people you meet.

Part of the already quoted German Academy statement bears repeating here: “Wearing a mouth and nose protection in public protects others and reduces the spread of the infection, thus indirectly lowering the risk of becoming infected. To a limited extent, mouth and nose protection also serves directly to protect oneself.” (See also Figure 5 in Huang, 2020).

Finally, citing Robling (2020)’s response to Greenhalgh et al. (2020): “Care should be exercised to ensure that variable uptake does not reinforce existing health inequalities and so perpetuate the effects of Tudor Hart’s Inverse Care Law”.


Greenhalgh Trisha, Schmid Manuel B, Czypionka Thomas, Bassler Dirk, Gruer Laurence. “Face masks for the public during the covid-19 crisis” BMJ 369 (2020): m1435. URL

Greenhalgh Trisha, Howard Jeremy. “Masks for all? The science says yes.” Fast.ai (2020). URL

Hedlund James. “Risky business: safety regulations, risk compensation, and individual behavior.” Injury prevention 6.2 (2000) : 82-89. URL

Howard, J.; Huang, A.; Li, Z.; Tufekci, Z.; Zdimal, V.; van der Westhuizen, H.; von Delft, A.; Price, A.; Fridman, L.; Tang, L.; Tang, V.; Watson, G.L.; Bax, C.E.; Shaikh, R.; Questier, F.; Hernandez, D.; Chu, L.F.; Ramirez, C.M.; Rimoin, A.W. “Face Masks Against COVID-19: An Evidence Review.” Preprints (2020), 2020040203. URL

Huang Sui. “COVID-19: Why we should all wear masks.” Medium (2020). URL

Javid Babak, Weekes Michael P, Matheson Nicholas J. “Covid-19: should the public wear face masks?” BMJ 369 (2020) : m1442. URL

Kasting Monica L., Shapiro Gilla K., Rosberger Zeev, Kahn Jessica A., Zimet Gregory D. “Tempest in a teapot: A systematic review of HPV vaccination and risk compensation research.” Human Vaccines & Immunotherapeutics 12.6 (2016): 1435-1450. URL

German Academy (Nationale Akademie der Wissenschaften Leopoldina). “2nd Ad-hoc-Statement: Coronavirus Pandemic–Measures Relevant to Health.” (2020) 3 pages. URL

Robling Michael R. “Rapid Response: Face masks and reducing health inequalities.” BJM. URL

Taleb Nassim Nicholas. “(Anti) Fragility and Convex Responses in Medicine.” International Conference on Complex Systems. Springer, Cham (2018). URL; arXiv



Nous sommes des académiques belges, francophones et néerlandophones, décidés à intervenir dans le débat public sur des questions générales qui ne ressortissent pas à nos champs stricts de spécialisation.

Wij zijn Franstalige en Nederlandstalige Belgische academici die besloten hebben tussen te komen in het maatschappelijk debat over algemene onderwerpen die niet tot onze strikte specialismen behoren.