Do face masks protect against the new coronavirus?
“There is a lot of contradicting information coming out about the use of face masks. Do face masks provide any protection or not?”
Question from a Full Fact reader
There is little dispute that clinically-approved masks, including respirators and surgical face masks, help reduce the spread of the new coronavirus in healthcare settings.
However, the advice on the general public wearing masks when out in the community varies by country. For many countries in Asia, wearing a mask in public spaces has been the norm since the outbreak of the new coronavirus.
Over the last few weeks, various European cities and countries have also begun to enforce the use of face masks in community settings, in what appears to be a worldwide shift in opinion.
As of 9 April 2020, Public Health England (PHE) is not advising members of the public that are not ill to wear face masks.
Dr Jake Dunning, Head of Emerging Infections and Zoonoses at Public Health England, said: “Face masks play a very important role in clinical settings, such as hospitals, and for people with symptoms. However, there is very little evidence of widespread benefit”.
On the other hand, the World Health Organisation’s (WHO) advice, published on 6 April 2020, says that “wearing a medical mask [in a community setting] is one of the prevention measures that can limit the spread of certain respiratory viral diseases, including COVID-19”.
Importantly, the WHO warns that face masks are not a replacement for other protective measures, such as hand hygiene or social distancing. They may be effective when combined with those measures.
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Why do facemasks work in theory?
NHS advice says that anyone with Covid-19 symptoms should be self-isolating and should not leave the house, so wearing a facemask in public should not, in theory, reduce your chances of catching the illness from someone who is already ill.
However, the evidence suggests that some people with Covid-19 are contagious before showing any symptoms of illness. Indeed, some infected people never show symptoms at all.
Because the virus is commonly transmitted via exhaled droplets this means that mask wearing for people who appear healthy can help to stop transmission of the new coronavirus virus to other people. This is known as source control.
The key point is that the benefit from masks is not that they stop people catching the virus, but that they might help to stop people spreading it.
Not all masks are created equal
In it’s guidance, the WHO makes clear that it is referring to surgical or medical masks, not homemade masks. Surgical or medical face masks are loose-fitting masks that cover the mouth and nose and are affixed to the head by straps. They contain fine fibres that act as filters to collect hazardous particles.
Cloth masks are washable homemade fabric masks and clothing items, such as scarves and bandanas, that are worn in a way to cover the mouth and nose. Cloth masks aim to create a barrier against large aerosol droplets leaving the wearer and reaching the environment.
Cloth masks are not regulated so the protection offered will vary by mask. The only published randomised controlled clinical trial of cloth masks found far higher rates of infection when healthcare workers wore cloth masks compared to medical masks.
Whilst the WHO hasn’t recommended the use of cloth masks, disease control agencies from the US and the EU have now said that these types of masks may help reduce the spread of Covid-19.
On 3 April 2020, the US Centres for Disease Control and Prevention updated its advice to say it “recommends wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies) especially in areas of significant community-based transmission”. A video is included that shows members of the public how to create their own mask from a household item.
The European Centre for Disease Prevention and Control advised on 6 April 2020 that “the use of non-medical face masks made of various textiles could be considered, especially if – due to supply problems – medical face masks must be prioritised for use as personal protective equipment by healthcare workers.” They write that “this is based on limited indirect evidence supporting the use of non-medical face masks as a means of source control.”
The authors of the clinical trial of cloth masks, mentioned above, have said that “the physical barrier provided by a cloth mask may afford some protection, but likely much less than a surgical mask or a respirator.” They further explain that improper disinfection and washing of the cloth masks likely contributed to the findings in their study.
Official sources stress that other protective measures, including social distancing and hand hygiene remain as important to slow the spread of the virus.
There are reasons why use of surgical masks in the community may not be advised
A major issue with widespread face mask use is that it can cause prices of these items to rise and lead to shortages in respirators and surgical masks for frontline health staff. The NHS is currently experiencing shortages of personal protective equipment including face masks.
Another potential issue listed by the WHO is that mask wearing may create a false sense of security, which could lead to people not following other essential measures.
Where local authorities advise that masks are worn in public, the WHO writes that “best practices should be followed about how to wear, remove, and dispose of them, and for hand hygiene after removal”.
Dr Dunning at PHE says that “in terms of being protected against other people’s infections when doing usual activities - such as an essential shop at the supermarket - the most effective thing you can do is to wash your hands frequently and use tissues when you cough or sneeze, or cough into your arm.”