< Masks

Where and when should I put on a mask?

Text updated on 2020-09-03


You don't want to contaminate others or get COVID-19? Here are the places, locations, and situations in which we advise you to put on a mask or not. Our advice and recommendations take into account current scientific data and are independent of the regulations in force in each country.

Outdoors, there is a very low risk of droplet contamination, emitted from the mouth and nose, when we breathe close to someone who has COVID-19.

Do we have to put a mask on outside?

Not when walking in the open air in a little frequented place, if you are sure not to start a discussion with someone, if you avoid close encounters, and if you stay more than two meters away to greet each other.

Yes in a high-traffic area in a region where the COVID-19 epidemic is active (e.g., there are many cases of COVID).

By bicycle or jogging: no.

Indoors, there is a risk of contamination by droplets and aerosols emitted and breathed in, but also by aerosols that can remain suspended in the air for several hours.

Do we have to put a mask on inside?

At home: no, unless you invite people with whom you do not have recurring close relationships.

In a well-ventilated place with open windows: no, if you can stay away from others, and for a short time.

In the bathroom: yes. Bathrooms are an enclosed and confined area, and flushing produces an aerosol that could be a contaminant.

In the elevator, yes. See our advice Taking the elevator.

In the lobby of your building: yes, because it is an enclosed and often poorly ventilated.

At the office: yes, if you share your office with others or if others need to enter your office, and if you cannot air the room continuously. See our tips Going to the office.

At the barbershop, yes. Two hairdressers with COVID-19 did not contaminate any of their 139 clients, all of whom were wearing masks.

At the supermarket: yes. See our advice Going to a store.

In restaurants and bars: it is not possible to put on a mask while eating or drinking! Several cases of contamination have occurred in restaurants, always indoors in poorly ventilated spaces. No contamination has been described on the outdoor patio. We therefore advise you to eat on the outdoor terrace or in a well-ventilated place.

In a place where you're close to people singing: yes. Many cases of contamination have occurred in places where people sing, such as the evangelical gathering in Mulhouse or a karaoke bar in Hong Kong.

At the movies: yes. It's an enclosed, air-conditioned space. The virus survives longer in the cold than in the heat.

At the swimming pool: yes in the change rooms and bathrooms, no in the showers and in the water! Avoid the bathrooms if possible. See the question Swimming pool and COVID : can I go to the pool in times of the COVID-19 epidemic?.

On the bus, subway, tram, train: yes. Cases of COVID contamination in public transport have been observed. See our advice Taking the bus/metro

In the taxi: Yes. The occupations most at risk of catching SARS-CoV-2 coronavirus are, after health care workers, bus and taxi drivers, and transport workers. See our advice Taking a taxi.

In your car: no if you are alone or with people in your household, yes if you are travelling with people outside your household. See our advice Taking the car, alone or in a group.

To be effective, the mask must cover the nose and mouth well. If you need to make a phone call, do not remove your mask. Sound passes very well through the mask.


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Sources

The analysis of 318 cases where one person contaminated at least 2 other people in China (for a total of 1,245 people with COVID-19) reveals that the majority of the contaminations took place in a closed space, mainly house and transport, but also in restaurants, and that only one contamination took place following an open air conversation with a person returning from Wuhan.

Qian, H., Miao, T., Li, L. I. U., Zheng, X., Luo, D., & Li, Y. (2020). Indoor transmission of SARS-CoV-2. medRxiv.

In Japan, many cases of "cluster" contamination have occurred in closed places: a sports hall, restaurant boat, hospital, festival where there were tents with minimal ventilation for eating.

Nishiura, H., Oshitani, H., Kobayashi, T., Saito, T., Sunagawa, T., Matsui, T., ... & Suzuki, M. (2020). Closed environments facilitate secondary transmission of coronavirus disease 2019 (COVID-19). medRxiv.

Compilation of 135 cases of COVID-19 contamination: analysis of the table provided by the authors indicates that more than 95% of the cases are indoor transmissions. For the remaining 5%, it is not clear whether transmission occurred outdoors. For example, contamination on construction sites may have occurred in construction huts.

Leclerc, Q. J., Fuller, N. M., Knight, L. E., Funk, S., Knight, G. M., & CMMID COVID-19 Working Group. (2020). What settings have been linked to SARS-CoV-2 transmission clusters? Wellcome Open Research, 5(83), 83.

60 members of a choir gathered in a room to sing for 2.5 hours on March 10, 2020 in Washington state, USA. They kept a safe distance, used hydro-alcoholic solutions, but did not put on masks. Three weeks later, 45 of them tested positive for COVID-19.

Los Angeles Times article of March 29, 2020.

During a concert at the Concertgebouw in Amsterdam, none of the 1,000 spectators seem to have been contaminated despite the length of the concert (a Bach Passion) and the strong contamination of the choir. The spectators were seated relatively far away from the choir.

Laspière, V.T. (2020) The Netherlands: four deaths from coronavirus after a choir concert. France Musique. 11th May 2020.

The mask blocks large droplets and breaks the airflow out of the mouth.

Leung, N.H.L., Chu, D.K.W., Shiu, E.Y.C. et al. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat Med 26, 676-680 (2020).

A symptomatic hairdresser tested positive for COVID-19. She infected her colleague, but none of the 139 clients developed symptoms. 67 clients were tested and none tested positive. All the clients wore masks.

Hendrix, M. J. (2020). Absence of apparent transmission of SARS-CoV-2 from two stylists after exposure at a hair salon with a universal face covering policy-Springfield, Missouri, May 2020. MMWR. Morbidity and Mortality Weekly Report, 69.

On a flight from Italy to South Korea, a 28-year-old was infected when she took off her mask to go to the bathroom. Of the 299 passengers on that flight, 6 asymptomatic people later tested positive for the SARS-CoV-2 coronavirus and one of them had used the same bathroom. The 18 cabin crew and medical personnel were not contaminated. They all wore masks.

Bae, S. H., Shin, H., Koo, H. Y., Lee, S. W., Yang, J. M., & Yon, D. K. Asymptomatic Transmission of SARS-CoV-2 on Evacuation Flight. Emerging infectious diseases, 26(11).

A man who had put his mask on incorrectly was contaminated during a flight from Singapore to Hangzhou, China on January 24, 2020. On the plane, he sat with his mask in the wrong position for an hour next to two asymptomatic people who then tested positive for SARS-CoV-2 coronavirus, because he talked to his wife and child who were next to him. The other people sitting next to the infected people were not infected. They all wore masks.

Chen, J., He, H., Cheng, W., Liu, Y., Sun, Z., Chai, C., ... & Shi, X. (2020). Potential transmission of SARS-CoV-2 on a flight from Singapore to Hanghzou, China: An epidemiological investigation. Travel Medicine and Infectious Disease, 101816.

Study of 961 patients with COVID-19 in Hong Kong between December 2019 and April 2020 and the cause of their contamination. Non-masked" leisure activities, such as eating and drinking in restaurants and bars, singing in a karaoke bar, or playing sports in a gym, led to significantly more cases of contamination than "masked" work environments.

Cheng, V. C., Wong, S. C., Chuang, V. W., So, S. Y., Chen, J. H., Sridhar, S., ... & Yuen, K. Y. (2020). The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2. Journal of Infection.

Study of two groups participating in an event, each group being in a different bus for one and a half hours with a single asymptomatic COVID case in one of the buses. The probability of being infected was 11.4 times higher in the bus with the infected person, regardless of the distance to the infected person, demonstrating aerosol contamination in an enclosed space for an extended period of time.

Shen Y, Li C, Dong H, et al (2020) Community Outbreak Investigation of SARS-CoV-2 Transmission Among Bus Riders in Eastern China. JAMA Intern Med. Published online September 01, 2020. doi:10.1001/jamainternmed.2020.5225

The authors present a simple guide to assess the risk of COVID transmission based on location, level of occupation, length of contact, and whether or not a mask is worn. They emphasize that physical distancing should be implemented in conjunction with other measures such as hand hygiene, cleaning, occupancy, and management of indoor space and air, and the use of masks.

Jones, N. R., Qureshi, Z. U., Temple, R. J., Larwood, J. P., Greenhalgh, T., & Bourouiba, L. (2020). Two meters or one: what is the evidence for physical distancing in covid-19?. bmj, 370.

Further reading

Do I have to wear a mask inside / outside?

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

Can a mask be reused?

Is the SARS-CoV-2 coronavirus transmitted by aerosols?

How does she get COVID-19 ?

How do you put on and take off your mask?

What are the different types of masks?

Why is it recommended not to wear a surgical mask for more than 4 hours?