29 March 2021
The COVID-19 pandemic took the world by surprise, leading to frenzied debates about how governments should respond. Perhaps the most confusing and divisive of these debates surrounds the use of face masks, with both scientists and politicians presenting mixed messages.
The World Health Organization (WHO) initially recommended that medical masks should only be used by healthcare workers and COVID-19 patients – advice that was welcomed by governments concerned that personal protective equipment (PPE) might run out. Meanwhile, public-led movements promoted the use of simple fabric masks, even home-made ones using handkerchiefs or T-shirts, as effective barriers to block SARS-CoV-2, the virus that causes COVID-19.
Eventually, on 5 June the WHO issued new advice that the general public should wear non-medical, fabric masks where physical distancing is not possible, for example in shops1. This guidance has been applied in most countries as an extra protective measure while communities emerge from lockdown restrictions.
In early July, the Ministry of Industry in Saudi Arabia announced plans to increase their production of masks from 2.5 million up to 10 million masks every day2. This strongly indicates the intention that masks will play a major role in the country’s ‘return to normality’, allowing people to attend weddings, funerals and beauty salons.
However, many scientific questions remain unanswered. How effective are fabric masks compared to bespoke PPE medical masks? Can masks be sterilized and re-used? Will they protect the wearer, or just people around them?
A major sticking point is that there has not been enough time to gather the gold standard of scientific evidence – fully peer-reviewed, replicable randomized control trials specifically testing masks against SARS-CoV-23. Some research groups have reported data for small numbers of patients, showing that a large percentage of the viral load is blocked by masks, but those results are inconclusive until they are fully checked.
“It is scientifically proven that wearing good quality masks by the population at risk will significantly decrease the spread of any respiratory virus spreading via droplets,” says pharmacoepidemiologist Islam Anan, the chief executive officer of Accsight (Healthcare Integrated Solutions) and a lecturer in the Faculty of Pharmacy at Ain Shams University in Cairo.
“The top evidence that wearing masks can be a pandemic stopper is a systematic review published in The Lancet7, analysing 216 studies and over 25,000 cases. All studies were conclusive to the fact that wearing high quality masks aids in preventing infection, especially alongside eye protection.”
Anan also points to powerful epidemiological modelling studies8,9 that examine the impact of different scenarios, varying mask quality and the percentage of the population wearing masks. “These very comprehensive studies clearly demonstrate that masks will decrease [the infection rate] R0,” he says.
For now, our best shot is to look to established work on masks with other viruses such as influenza, which is of very similar size to SARS-CoV-2. Lab and modelling studies had found that masks could be effective tools in managing an epidemic by blocking a large percentage of the influenza viral load from escaping a wearer’s mouth7, though there is less evidence that they protect the wearer themselves8. Home-made fabric masks blocked fewer influenza viruses than commercial masks, but were certainly better than no protection9.
Another hazard that masks can protect against is air pollution, especially PM2.5 – particles smaller than 2.5 micrometres in diameter which stay in the air for long periods and can penetrate deep into the lungs. When 239 scientists wrote a commentary in early July urging the WHO to recognize mounting evidence that many microscopic droplets containing viable SARS-CoV-2 viruses can be classified as aerosols, protection from these tiny particles became particularly important10. They are light enough to stay aloft in the air over tens of meters, complicating social distancing efforts considerably.
Lab experiments include pumping polluted air through masks of different types. These have shown that professional-standard masks can block up to 99% of PM2.510,11,12. Tests on fabric masks are limited, but one study11 showed that a thin cotton handkerchief could block over 28% of PM2.5.
This might seem poor, but these tests greatly underestimate the effectiveness of masks, for several reasons. Firstly, the detectors used in such studies measure particles ten times smaller than even SARS-CoV-2 itself. Secondly, most cotton masks are a lot thicker than a single handkerchief. Moreover, most droplets emerging from people’s mouths are larger than PM2.5, and the problematic aerosols arise from larger droplets evaporating once they are well away from the mouth.
Perhaps the strongest evidence in favour of using masks in the current pandemic arises from epidemiological studies of state-13 or country-wide14 COVID-19 data. A statistical analysis published in June reports the extraordinary finding that “in countries with cultural norms or government policies supporting public mask-wearing, per-capita coronavirus mortality increased on average by just 15.8% each week, as compared with 62.1% each week in remaining countries.”
Given these findings, many governments have made masks mandatory in different situations, and started looking for ways to sterilize and reuse masks so that they do not run out or create a waste problem. A recent review paper states that the most promising methods for sterilizing masks against SARS-CoV-2 are those using hydrogen peroxide vapor, ultraviolet radiation, moist heat, dry heat or ozone gas, while other methods such as steam or microwave treatment are not recommended15.
Perhaps the burden of proof in the masks debate actually lies with those arguing against them. After all, it seems common sense that putting any barrier in front of your mouth will block at least some infectious droplets. And, importantly, no scientific studies have found evidence that masks could increase anyone’s risk of infection.
So, for now the only reasonable arguments against mask use are social, political and economic. For instance, people may feel embarrassed or stigmatized when wearing masks, making them less likely to visit shops and assist in their country’s economic recovery. This behaviour has been observed in previous epidemics, and supports the notion that mask-wearing is best as a universal policy for everyone. That way, a mask can be a positive signal of solidarity in society, rather than something that labels a sick person.
On the other hand, some people might proudly wear a mask with a false sense of security, so they neglect other mitigation measures like physical distancing and hand-washing.
This dilemma touches on an interesting area of psychology called risk compensation, which often arises when new safety laws are introduced. For example, if we make people wear helmets on motorcycles and seatbelts in cars, will they be more reckless because they think they can’t be hurt? Studies of these situations show that, while a few individuals might take more risks, their behaviour is dwarfed by that of society as a whole, resulting in overall improved safety and well-being16.
Therein lies the key – small measures, applied widely, can provide large benefits for the population. Masks are clearly not a panacea that will end the COVID-19 pandemic, but neither are they a significant burden for an individual to bear. For those who have never lived through an epidemic before it may seem strange, but wearing a simple face covering really could save lives.
“Masks stand on the first line of defence against COVID-19 along with eye protection, social distancing and hand washing,” says Anan. “It is the answer we have now until vaccines or highly effective treatments are available, and a necessity after the re-opening of economies, to avoid any rebound.”
- World Health Organization. Advice on the use of masks in the context of COVID-19. (5 June 2020) | article
- Saudi Arabia plans to produce 10 million masks daily | article
- Howard, J. et al. Face masks against COVID-19: An evidence review. PNAS (April 2020) | article
- Chu, D.K et al. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. The Lancet 395, 1973-1987 (2020). | article
- Eikenberry et al. To mask or not to mask: Modeling the potential for face mask use by the general public to curtail the COVID-19 pandemic. Infectious Disease Modelling 5, 293-308 (2020) | article
- De Kai et al. Universal Masking is Urgent in the COVID-19 Pandemic: SEIR and Agent Based Models, Empirical Validation, Policy Recommendations. Physics and Society | article
- Brienen N.C. et al. The effect of mask use on the spread of influenza during a pandemic. Risk Anal. 30, 1210-1218 (2010) | article
- Cowling B.J. et al. Face masks to prevent transmission of influenza virus: a systematic review. Epidemiol Infect. 138, 449-456 (2010) | article
- Davies A. et al. Testing the efficacy of homemade masks: Would they protect in an influenza pandemic? Disaster Med Public Health Prep. 7, 413-418 (2013) | article
- Morawska, L. & Milton, D.K. It is time to address airborne transmission of COVID-19. Clinical Infectious Diseases, ciaa939 (2020) | article
- Cherrie JW, et al. Effectiveness of face masks used to protect Beijing residents against particulate air pollution. Occup Environ Med. 75, 446-452 (2018) | article
- Langrish JP, et al. Beneficial cardiovascular effects of reducing exposure to particulate air pollution with a simple facemask. Part Fibre Toxicol. 6 (2009) | article
- Lyu, W. & Wehby, G.L. Community use of face masks and COVID-19: Evidence from a natural experiment of state mandates in the US. Health Affairs 39 (2020) | article
- Leffler, C. et al. Association of country-wide coronavirus mortality with demographics, testing, lockdowns, and public wearing of masks. medRxiv | article
- Carlos Rubio-Romero J. et al. Disposable masks: Disinfection and sterilization for reuse, and non-certified manufacturing, in the face of shortages during the COVID-19 pandemic. Saf Sci. 129, 104830 | article
- Pless, B. Risk compensation: Revisited and rebutted. Safety 2, 16 (2016) | article