Fresh air unmasked

As the UK government announce an end to covid-19 restrictions in England, Christine Peters and Tom Lawton discuss why they will still be wearing a mask

Masked or unmasked? That is the defining question of the hour.

This pandemic-age dilemma has boomeranged into sharp focus once again with the much hyped “Freedom Day” looming on 19 July in England. Memories of early 2020 re-play when medical experts and the government are once again at loggerheads over the likely utility of general public use of face coverings or masks. During the first wave of covid-19 the debate became an ideological touchstone in USA politics, while East Asian countries looked on bemused at the song and dance being made in Europe about something that is a long standing, culturally normalised practice in East Asia. 

In the UK some high profile medics initially denounced the idea as dangerous and risky, while others strongly supported the measure based on a mechanistic understanding of transmission and historical evidence base. The objections cited against masks have ranged from masks being a fomite risk, the risk that the general public won’t use them properly, increased risk taking behaviours, childhood developmental issues, an impingement on individual freedoms, and concerns about depleting stock for healthcare professionals. [1] 

Over the 18 months of the pandemic there has been a lack of evidence to demonstrate the postulated risks of harm from masks, despite the colossal scale of use. Meanwhile data have amassed on their effectiveness as a public health measure.[2] A Danish randomised controlled trial on mask use suggested an 18% reduction in infections for individuals given a mask recommendation, a result which did not reach statistical significance, but was impressive given that their main benefit appears to be to others around the wearer, with a 79% reduction in secondary cases reported in one study. [3,4] Delays in implementing mask use during the first covid wave could be considered as lost time at the critical early stages of the pandemic, by spurning an effective public health intervention. By extension, dropping the use of masks while the numbers of covid-19 cases escalate in England, and while vaccine induced population level immunity is not yet achieved, has come under huge criticism from public health experts and healthcare professionals. 

This ongoing masking controversy can be seen as a demonstration of both the misapplication of the precautionary principle as well as a fundamental misunderstanding of the primary route of covid transmission—airborne transmission. 

A major issue with the precautionary principle is that it can be formulated in different ways, with almost opposite results, enabling all sides to lay claim to applying it. While others exist, three relevant potential formulations have been described:

Firstly the prohibitory formulation which promotes inaction: 

“Activities that present an uncertain potential for significant harm should be prohibited unless the proponent of the activity shows that it presents no appreciable risk of harm”[5]

Secondly the cautious formulation which reduces harms:

“Activities that present an uncertain potential for significant harm should be subject to best technology available requirements to minimize the risk of harm unless the proponent of the activity shows that they present no appreciable risk of harm”[5]

Thirdly the active formulation which promotes action to reduce harms

“Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent [harm]”[6]

A prohibitory formulation can make sense the majority of the time, when the status quo is safe. The theoretical risks of masks could be argued as reasons for inaction until evidence on the benefits or safety were available. However, in a pandemic, with exponentially increasing cases and hospitalisations, inaction can no longer be considered safe, and must be considered just as much of a choice as taking action. A prohibitory formulation becomes meaningless when faced with multiple active choices and we must move to an approach of reducing harms.

In the second “cautious” approach to the precautionary principle we are guided to take action—in this case to use the best available technology to minimise harms. It could be argued however that this only includes the use of proven technologies As data accumulate on the effectiveness of masks, particularly Respiratory Protective Equipment for health and social care workers, this becomes increasingly applicable. 

This leads to the third and probably most famous formulation, which was created to prevent uncertainty being used as an excuse for inaction on climate change, and is therefore probably most relevant to the pandemic where inaction cannot be considered harmless. This principle encourages action in the face of scientific uncertainty, and has precedent even outside emergency situations, despite demands for the status quo to remain until “gold standard” randomised controlled trials (RCT) have been conducted.[7] Case-control studies are the basis for campaigns against smoking.[8] A nation of babies sleep on their backs despite a lack of RCT evidence.[9] And first principles and cohort studies have convinced many of us to treat covid-19 patients in hospitals with continuous positive airway pressure therapy.[10]

The first principles of airborne transmission coupled with the evidence of effectiveness to date is a strong foundation for the precautionary principle to be applied in favour of a policy that will reduce transmission and is especially relevant in settings where transmission has been high, such as hospitals and care homes. 

Wear a mask. We will.

Christine Peters, consultant microbiologist, NHS Greater Glasgow and Clyde. 

Tom Lawton, consultant critical care, Bradford Teaching Hospitals NHS Foundation Trust.

Competing interests: CP and TL are part of FreshAirNHS, campaigning for acknowledgement that #COVIDisAirborne and for #ventilation and airborne protections in healthcare.


1 Lazzarino AI, Steptoe A, Hamer M, Michie S. Rapid Response: Covid-19: important potential side effects of wearing face masks that we should bear in mind. BMJ 2020:m2003.

2 Howard J, Huang A, Li Z, Tufekci Z, Zdimal V, Westhuizen H-M van der, et al. An evidence review of face masks against COVID-19. PNAS 2021;118.

3 Bundgaard H, Bundgaard JS, Raaschou-Pedersen DET, von Buchwald C, Todsen T, Norsk JB, et al. Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers. Ann Intern Med 2021;174:335–43.

4 Wang Y, Tian H, Zhang L, et al. Reduction of secondary transmission of SARS-CoV-2 in households by face mask use, disinfection and social distancing: a cohort study in Beijing, China. BMJ Global Health 2020;5:e002794. 

5 Stewart RB. Environmental regulatory decision making under uncertainty. In: Swanson T, editor. An Introduction to the Law and Economics of Environmental Policy: Issues in Institutional Design, vol. 20, Bingley: Emerald Group Publishing Limited; 2002, p. 71–126.

6 Antrim LN. The United Nations Conference on Environment and Development. In: Goodman AE, editor. The Diplomatic Record 1992-1993. 1st ed., Routledge; 2019, p. 189–210.

7 Adashek JJ, Kurzrock R. Balancing clinical evidence in the context of a pandemic. Nat Biotechnol 2021;39:270–4.

8 Doll R, Hill AB. Smoking and Carcinoma of the Lung. Br Med J 1950;2:739–48.

9 Fleming PJ, Blair PSP, Bacon C, Berry PJ. Sudden Unexpected Death in Infancy. The CESDI SUDI Studies 1993-1996. The Stationary Office, London; 2000.

10 Lawton T, Wilkinson K, Corp A, Javid R, MacNally L, McCooe M, et al. Reduced critical care demand with early CPAP and proning in COVID-19 at Bradford: A single-centre cohort. Journal of the Intensive Care Society 2021:17511437211018616.