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What do we know so far about face masks and their ability to prevent COVID-19? | Covid-19 Expert Database What do we know so far about face masks and their ability to prevent COVID-19? | Covid-19 Expert Database

COVID-19 Expert Database


What do we know so far about face masks and their ability to prevent COVID-19?

Last modified on 13 August 2020

What our experts say

As per the World Health Organization (WHO), wearing masks is part of an overall strategy to suppress the transmission of COVID-19, along with maintaining at least 2 meters (6 feet) distance and frequently washing your hands.

There are generally two kinds of face masks that are available - medical (or surgical) masks and non-medical (or fabric) masks. Medical masks can protect people from getting infected as well as prevent the spread from those that are infected. Therefore, WHO recommends medical masks to be worn by health workers, care givers of patients infected with COVID-19, anyone who has mild symptoms of COVID-19, people with other health conditions which make them more susceptible to COVID-19, as well as people who are 60 years or older because they have a higher risk of getting infected with COVID-19.

WHO advises that non-medical masks should be worn in areas where there is high transmission of COVID-19, crowded places where at least 2 meters (6 feet) physical distancing is not possible, on public transport, in shops and other closed areas. COVID-19 can be spread by people without symptoms, as they may not know that they are infected but are equally capable of spreading the virus. Hence, masks should be worn in public settings.

The U.S. Centers for Disease Control and Preventions (U.S. CDC) suggests that masks with exhalation valves or vents will not help prevent the spread of COVID-19 from the person wearing such a mask to others, therefore these masks should not be used for that purpose. Wearing a face mask protects others from you when you cough, sneeze, talk, or just breathe, particularly indoors or when standing close to someone. Masks also partially protect the wearer from inhaling the virus from other people nearby, and prevents people from touching their mouth and nose. Mask wearing is a fundamental element of pandemic response for respiratory illnesses because masks act as a physical barrier from the release of infectious respiratory droplets that may come from your mouth or nose when you speak, sing, sneeze or cough. In addition to social distancing measures (maintaining 6 feet or 2 meters between people), face masks are recommended to prevent the spread of COVID-19, even in hot climates. There is no evidence that surgical masks or cloth masks lower oxygen levels at all. It is important to use a mask that allows you to breathe comfortably while talking and walking and that fits well on your face. For safety, masks should not be worn by children under the age of 2, by people who have trouble breathing, or anyone who is unconscious or unable to remove the mask without assistance. We do not know yet if face shields alone provide enough protection against COVID-19. Currently, face shields are not recommended as an alternative to face masks. Ideally, face shields should be used in combination with face masks.

This entry was updated with new information on Aug 13, 2020

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Context and background

There has been a lot of debate about how effective wearing face masks are in preventing the transmission of COVID-19. Part of the reason for this is the confusion that occurred in February and March of 2020 when the World Health Organization (WHO) and the United States Centers for Disease Control and Prevention (U.S. CDC) advised the public not to wear masks. This guidance was based on several important points:

1) These agencies did not think there was enough proof that the general public should be wearing masks unless they were infected with COVID-19 or they were around people infected with COVID-19. This is because it wasn’t known yet that people could still spread COVID-19 even if they had no symptoms; 2) There was a shortage of masks for doctors and healthcare professionals ; 3) The difference in the types of masks and materials that were available; and 4) The research that is still in progress about how COVID-19 spreads (like through droplets, surfaces, etc.).

However, the research has evolved since the beginning of the pandemic, and we now have enough proof that masks are effective at preventing the spread of COVID-19. This is why once the international scientific community had reached that consensus, the WHO, the U.S. CDC, and other health organizations changed their recommendations and now advise people to wear masks while in public settings. It is common to change policies as new information becomes available. Because COVID-19 is a new virus, we are still learning more every day and changing and improving our recommendations.


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  1. Facial Skin Temperature and Discomfort When Wearing Protective Face Masks: Thermal Infrared Imaging Evaluation and Hands Moving the Mask (IJERPH
  2. Effects of wearing N95 and surgical facemasks on heart rate, thermal stress and subjective sensations (IAOEH)
  3. Does Wearing a Face Mask Reduce Oxygen—and Can It Increase CO2 Levels? Here’s What Experts Say (Health)
  4. Face masks for the public during the covid-19 crisis (BMJ)
  5. From the Frontlines: The Truth About Masks and COVID-19 (ALA)
  6. Does prolonged wearing of a facemask cause harm? (Vanderbilt)
  7. Partly false claim: Continually wearing a mask causes hypercapnia (Reuters)
  8. Killer COVID-19 Masks? The Truth About Trapped Carbon Dioxide (Hartford Healthcare)
  9. What People With Asthma Need to Know About Face Masks and Coverings During the COVID-19 Pandemic (AAFA)
  10. Severe Acute Respiratory Infections Treatment Centre (WHO)
  11. Will an air cleaner or air purifier help protect me and my family from COVID-19 in my home? (U.S. EPA)
  12. Air purifiers: A supplementary measure to remove airborne SARS-CoV-2 (BE)
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