< Masks

Why put on a mask?

Text updated on 2020-05-03


To put on a mask is to protect others, and also to protect yourself. It's an essential barrier gesture when you don't know who's contagious or vulnerable.

Masks block droplets from the mouth and nose, which may contain infectious viral particles. The blocking mechanisms change with the size of the particles and are not only mechanical but also electrostatic. Masks stop larger particles and attract and trap charged particles (like a balloon attracts pieces of paper). The composition of the mask and its adhesion to the face are very important factors that influence its effectiveness.

Many individuals who are asymptomatic ("asymptomatic") or have no symptoms ("pre-symptomatic") or more ("post-symptomatic") produce large amounts of virus in saliva. Viral particles are present in droplets emitted into the air through the nose and mouth when speaking, singing, screaming, sneezing, coughing, or simply breathing. The mask, even a homemade one, helps to limit the spread of droplets carrying the virus that could infect others. So wearing a mask, in combination with (not as a substitute for) social distancing measures, helps to contain the transmission of the virus.

A recent study estimates that if at least 80% of the population wears a mask, then the number of infected people increases less rapidly than with social distancing alone and can prevent more deaths than unlimited confinement not associated with mask use. Nose and mouth" containment appears to be more effective than confining people and, thus, may reduce the spread of the virus and increase our well-being!

Please note that the mask offers no guarantee against the risk of indirect transmission through our hands, for example by touching a contaminated object and then placing one's hand near the mouth, or by rubbing one's eyes after shaking hands with a person who is a SARS-CoV-2 carrier and who has blown his or her nose.

The way you speak (quietly or loudly) as well as the way you cough has a significant impact on particulate emissions. It is recommended to avoid loud talking or coughing, even with a mask, during discussions between people 1-3 meters away.


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Sources

A study of 254 caregivers during the 2003 SARS outbreak shows that those who wore masks were less infected than those who did not.

Seto, W. H., Tsang, D., Yung, R. W. H., Ching, T. Y., Ng, T. K., Ho, M., ... & Advisors of Expert SARS group of Hospital Authority. (2003). Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS). The Lancet, 361(9368), 1519-1520.

A study that compared the prolonged use of a cloth mask over a whole day versus the successive wearing of 2 surgical masks in a hospital in Vietnam. Cloth masks have a higher risk of infection than medical masks due to moisture retention, the potential reuse of poorly washed cloth masks, and less filtration.

MacIntyre, C. R., Seale, H., Dung, T. C., Hien, N. T., Nga, P. T., Chughtai, A. A., Rahman, B., Dwyer, D. E., & Wang, Q. (2015). A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ open, 5(4), e006577.

Continuous use of masks reduces the transmission of the influenza virus from sick children to the adults who care for them.

MacIntyre, C. R., Cauchemez, S., Dwyer, D. E., Seale, H., Cheung, P., Browne, G., Fasher, M., Wood, J., Gao, Z., Booy, R., & Ferguson, N. (2009). Face mask use and control of respiratory virus transmission in households. Emerging infectious diseases, 15(2), 233-241.

Masks, even homemade ones, can function as barriers that reduce the distance of droplet dispersion.

Rodriguez-Palacios, A., Cominelli, F., Basson, A., Pizarro, T., & Ilic, S. (2020). Textile Masks and Surface Covers - A 'Universal Droplet Reduction Model' Against Respiratory Pandemics. medRxiv.

The mask reduces the amount of seasonal human coronavirus and influenza viruses in expired droplets and aerosols. Studies employed close to real conditions (no forced coughing, breathing for 30 min) to test the effectiveness of the home-made masks. PCR tests were performed on droplets of different sizes. The barrier action of the artisanal masks is very clear. It should also be noted that sick patients who do not cough may produce droplets containing viruses.

Leung, N. H., Chu, D. K., Shiu, E. Y., Chan, K. H., McDevitt, J. J., Hau, B. J., ... & Seto, W. H. (2020). Respiratory virus shedding in exhaled breath and efficacy of face masks. Nature Medicine, 1-5.

The mechanisms for blocking droplets and particles by masks are varied and change with the size of the particles.

Konda, A., Prakash, A., Moss, G. A., Schmoldt, M., Grant, G. D., & Guha, S. (2020). Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano.

Surgical masks and respirators: properties, materials, filtration mechanisms.

Institute of Medicine 2006. Reusability of Facemasks During an Influenza Pandemic: Facing the Flu. Chapter: 2 Characteristics of Respirators and Medical Masks. Washington, DC: The National Academies Press.

Viral loads do not differ significantly between asymptomatic and symptomatic people.

Zou, L., Ruan, F., Huang, M., Liang, L., Huang, H., Hong, Z., ... & Guo, Q. (2020). SARS-CoV-2 viral load in upper respiratory specimens of infected patients. New England Journal of Medicine, 382(12), 1177-1179.

Simulation of the progression of the epidemic with different scenarios of wearing a mask. If most of the population wears a mask, then the spread of the epidemic will be less than by social distancing and even indefinite confinement alone. On the other hand, if only half of the population wears a mask at the onset of the epidemic, the effect will not be so great. The effect of wearing the universal mask is most effective at the beginning of the epidemic, but also if it begins 50 days after the start of the epidemic rather than 75 days later. Countries that have mandated the use of masks (Taiwan, Japan, South Korea, several parts of China, Slovakia, Slovenia) show a smaller increase in the number of COVID cases. Video: https://www.youtube.com/watch?v=yfeW2l8G_W4eature=youtu.be

Kai, D., Goldstein, G.-P., Morgunov, A., Nangalia, ishal, & Rotkirch, A. (2020). Universal Masking is Urgent in the COVID-19 Pandemic: SEIR and Agent Based Models, Empirical Validation, Policy Recommendations. ArXiv.

The rate of particle emissions increases with the volume of the voice.

Asadi, S., Wexler, A. S., Cappa, C. D., Barreda, S., Bouvier, N. M., & Ristenpart, W. D. (2019). Aerosol emission and superemission during human speech increase with voice loudness. Scientific reports, 9(1), 1-10.

The velocity of the droplets emitted is greater when coughing than when talking.

Kwon, S. B., Park, J., Jang, J., Cho, Y., Park, D. S., Kim, C., ... & Jang, A. (2012). Study on the initial velocity distribution of exhaled air from coughing and speaking. Chemosphere, 87(11), 1260-1264.

Further reading

Do I have to wear a mask if I don't have any symptoms?

How do you put on and take off your mask?

How do you make your mask?

What are the different types of masks?