• This article goes over the types of masks that exist. It explores how effective are they at preventing transmission of coronavirus, according to the latest research.
  • It reviews the advice on masks and face coverings from public health organisations, and presents official guidance from several nations.
  • This is part of our rapid response content on COVID-19. You can view all our reporting on this topic under COVID-19

There is an ongoing debate about the role of face masks or other face coverings (such as home-made cloth masks or scarves) for the general public, as part of the strategy to limit transmission of COVID-19.

The novel coronavirus SARS-CoV-2 that causes COVID-19 is spread through two main routes:

  • droplet transmission: respiratory droplets are generated when someone coughs or sneezes. If someone is in close contact (within 1m) then they are at risk of being exposed to droplets through the mouth, nose and eyes.
  • contact transmission: contacting with the virus by touching contaminated surfaces. Transmission can occur if someone then touches their mouth, nose or eyes.

The role that face masks could play in limiting community transmission of the virus is of policy interest because people can be infected with the virus but have no symptoms (asymptomatic). They can also be infected but have not yet developed symptoms (pre-symptomatic). The question is whether transmission of the virus can be reduced if people in these categories cover their nose and mouth.

This is not straightforward since it depends on the type of face mask used, and the hygiene etiquette practised by those using them. Medical face masks could minimise the virus entering the body through the nose or mouth, and by reducing the transfer of the virus from contaminated hands when touching the face. However, face masks do not offer any eye protection.

Healthcare workers caring for patients with COVID-19 are at higher risk of catching the virus. As with any infectious disease, they follow protocols to use appropriate personal protective equipment (PPE) depending on the type and duration of patient contact. PPE includes masks, visors, gloves and gowns. Health care professionals and researchers working with viruses and other pathogens benefit from well-evidenced guidance, protocols and training in using this type of protective equipment.

The Department of Health and Social Care’s policy on the use of PPE outlines that health and social care workers are at higher risk of experiencing repeated contact and droplet exposure to the virus. Therefore, government guidance sets out detailed recommendations PPE that should be worn in:

Employers are mandated by health and safety legislation to provide appropriate protective equipment for their employees.

Face mask types

There is a variety of PPE used to control the transmission of infectious diseases. This ranges from sophisticated full-face respirators to simple disposable fluid-repellent medical masks. A simple medical face mask covers the nose, mouth and chin. They prevent droplets from reaching these parts of the wearer’s face and reduce the spread of infectious droplets from the person wearing it. All types of medical face masks are designed to meet quality standards.

  • FFP3 mask: a European standard disposable respirator that seals the nose and mouth and offers a very high level of filtration of particles in aerosols (99%).
  • N95 masks: an American standard disposable respirator that seals the nose and mouth, it offers a lower level of particle filtration (95%, equivalent to the European FFP2 standard).
  • Surgical masks: fluid resistant mask that covers the mouth and nose, but is not sealed.
An FFP3 mask, the European standard disposable respirator.
A FFP3 mask. The European standard disposable respirator. Image by Marco Verch

Other masks are available which do not meet such standards and are not used in medical settings. These include commercial or self-made masks, which may be made of cloth, paper or other materials.

Research on face masks

The main consensus emerging from the scientific literature is that the evidence base is inadequate.

There is no research on the role of masks worn by the general population on the transmission of SARS-CoV-2. There is some research on the role of masks in the transmission of influenza and other respiratory viruses.

The best way to test a health intervention is with a randomised control trial (RCT) – this allows one or more interventions to be tested against an alternative or doing nothing. In studies of masks, studies have compared a variety of the following: different mask types, masks with additional measures such as hand hygiene, and no masks at all. Scientists can also examine data from separate studies (like RCTs) that have looked at a health intervention by using an approach called a systematic review. This allows researchers to examine how effective a health intervention is, using the results from multiple studies and summarise the results.

Studying the role of face masks or other face coverings in limiting the transmission of respiratory viruses like SARS-CoV-2 is complicated by several factors:

  • respiratory viruses have different physical characteristics and may have different transmission routes.
  • there are many types of face mask; for some types of study researchers do not know which ones were worn.
  • study participants may not adhere to instructions to wear masks (such as duration, frequency).
  • control groups may wear masks even though they have been told not to.
  • studies need to be carefully controlled to minimise bias.

One systematic review searched for any studies of the impact of healthy people wearing masks to prevent COVID-19 transmission. It did not find any such studies. The study authors conclude that this highlights the need for research on this subject. Two subsequent reviews have been published as preprints (they have not been reviewed by other scientists yet).

A review on influenza prevention found that there was no evidence to suggest that masks reduced community transmission. Another recent systematic review found that respiratory illness transmission was very slightly reduced by mask wearing in general – the authors suggest this is at around 6%, but this is highly uncertain as the evidence is not strong. Effectiveness was very slightly higher through mask wearing by an infected person and their household contacts. The authors conclude that it is not possible to make accurate estimates of the degree of protection offered by facemasks based on the available evidence.

Other relevant information comes from single studies on other respiratory viruses, which may share similarities in transmission to SARS-CoV-2, such as influenza. There have been several studies looking at how effective masks are in preventing viral respiratory illness. Most have taken place in hospitals, rather than community settings. It is not always possible to draw firm conclusions from them and this can be for a variety of reasons – the study may be too small, be biased in some way or have been carried out a time when the levels of circulating respiratory viruses are low.

Two reviews compared different types of face protection to prevent influenza transmission and found that there was no difference between surgical masks and special respirator masks in preventing viral respiratory illness in healthcare settings. Some smaller studies from community settings are highlighted here:

Many studies report that compliance with wearing masks varies and this has an impact on their effectiveness. Compliance with mask wearing is related to cultural context.

Civilians wearing surgical masks while going about their day-to-day life in public.
Surgical masks are fluid resistant mask that cover the mouth and nose. They don’t form a “seal”. It’s not conclusive how effective they are in comparison to other mask types. Image Chanawit Sitthisombat

Cultural attitudes to face masks and face coverings

There are also cultural differences in the use of face masks that play a role in how they might be adopted by different communities. For example, they are widely used in some Asian countries, particularly since the outbreak of other diseases caused by other members of the coronavirus family, notably the outbreak of Severe Acute Respiratory Syndrome (SARS) in 2003.

In some cultures, face masks are used predominantly as part of hygienic practice (such as in Asia) whereas in others, it is more typically something only people who are unwell do (European and North American countries).

Differences in cultural practices can result in stigmatisation and exacerbate racially discriminatory behaviour towards those who wear masks as a precautionary measure by those who believe masks are associated with presence of disease.

People in a public transport hub with face masks. People from different culture wear face masks for different reasons.
In some some cultures, face masks are used predominantly as part of hygienic practice whereas in others, it is more typically something only people who are unwell do. Image Zhipeng Ya

Some research suggests that one advantage of universal face mask use is that it prevents discrimination of individuals who wear masks when unwell because everybody is wearing a mask. Other research suggests that wearing a face mask has a strong symbolic value as a public health measure, strengthening perceptions of personal control but also importantly, as a symbol of social solidarity.

According to a global public opinion tracker representative survey by YouGov in partnership with Imperial College London, as of 24 April, 13% of people in the UK reported wearing a face mask when in public places. Lower levels of usage were only reported in the Nordic countries: Sweden (6%), Norway (6%), Finland (4%) and Denmark (2%). By contrast, the highest levels of usage were reported in Thailand (90%), Italy (89%) and Taiwan (88%).

However, a representative survey of the UK by Ipsos MORI indicates that Government advice could change British people’s attitudes to wearing face masks, with 74% of the British public stating that they would follow advice if the Government formally recommends wearing masks to slow the spread of the coronavirus.

New research on masks

One clinical trial is registered so far to test the value of face masks in community settings.

This clinical trial of 6,000 people in Denmark, will compare wearing face masks with not wearing face masks. All participants will be instructed to follow national public health guidance. If they develop symptoms they will be tested during the study. They will all be screened at the end of the study to see if they have produced antibodies against COVID-19.

Advice from international public health organisations

International public health organisations have published guidance on the use of face masks in community settings, and how national decision-makers might approach making and sharing advice on the use of masks by the general public. One key point is that the actions that are most effective in limiting transmission are thorough hand washing and social distancing. Face masks are to be viewed as only one part of an approach that combines multiple public health measures to limit transmission.

World Health Organization (WHO)

The WHO has a detailed briefing on the use of masks in community settings, published on 6 April. WHO recommends that two groups of people should wear face masks:

  • people who are sick or have symptoms.
  • people caring for those who have COVID-19.

They state that there is no evidence that healthy people in the wider community are protected from respiratory infections by wearing a mask of any type. They also argue that wearing masks creates a false sense of security in the wearers, and they may be less attentive to proven hygiene measures such as hand washing and social distancing. There is also the potential for an increased risk of self- contamination through touching and reusing dirty masks.

A young person wearing a hand made mask over their face. Touching a mask can potentially contaminate it.
The WHO argues there is the potential for an increased risk of self- contamination through touching and reusing dirty masks. But there’s limited evidence substantiating this.

The WHO has advice for countries recommending the use of masks by the general public. It sets out guidelines for national decision-makers: the purpose of masks (source control or prevention), local exposure risk, vulnerabilities of different groups, local setting (e.g. densely populated urban area), feasibility of providing masks and mask type.

For those countries where masks are worn in accordance with local customs or national government advice, the WHO recommends that best practice in their use and disposal be adopted.

The European Centre for Disease Prevention and Control (ECDC)

The ECDC published a guide summarising the evidence, and outlining the pros and cons of using face masks as a public health measure against COVID-19 on 8 April. Key points:

  • source control: medical face masks may reduce transmission in the community through minimising the excretion of respiratory droplets from infected people who are unaware they carry the virus. Non-medical face masks are less effective than medical masks for source control.
  • protective effect: there is no evidence that non-medical face masks or other face coverings offer any protection to the wearer. Non-medical masks have low filter efficiency. One study showed that cotton masks were associated with a higher risk of penetration of microorganisms when compared to no masks.

They state that the use of face masks in the community should be seen as a complementary measure to other well-evidenced public health measures. Like the WHO they recommend that medical masks are prioritised for healthcare workers. They also echo WHO’s concern about masks offering wearers a false sense of security, and that inappropriate use could result in increased risk of transmission.

Policy debate about masks

One of the main arguments is that everyone should wear a mask because even if we don’t know it reduces risk, it does not do any harm.

A recent paper that recognises the limitations of the available evidence and the inconsistent interpretations of the research by public health agencies, cites the precautionary principle in advocating for the use of masks by the general public. They suggest that, even if we do not know if wearing masks reduces the risk of transmission, it would not do any harm.

The authors suggest that the public is highly motivated to comply with instructions for wearing face masks and that even a modest impact on transmission could have positive effects, such as reduced demand for hospital beds and ventilators. They argue that the negative impact of mask-wearing on other hygiene measures is not substantiated by evidence. They also contend that supply concerns of masks for healthcare workers is an argument to manufacture more masks, not to deny the public the opportunity to use them.

National policies

The UK Government does not recommend that the public should wear medical face masks or other face coverings, since this is not supported by evidence from research. It is unlikely that a strong evidence base derived from high quality randomised control trials will become available in the timeframes that government is being challenged on its decision about the use of masks by the media and in wider debate. In a House of Commons debate on 28 April, Michael Gove announced that the Government is seeking to produce masks that could be worn by the public.

The Scottish Government announced new guidance on face coverings on 28 April. The guidance highlights the principal importance of social distancing, hand and respiratory hygiene, and the limited evidence on the value of face coverings for the general population. It suggests there may be some benefit in wearing face coverings in certain situations. Examples are enclosed spaces where physical distancing is difficult, or where close contact with multiple people outside one’s household is likely. The advice refers to home-made covering made from cloth, or a scarf. The recommendation is not mandatory and will be reviewed as the situation evolves.

Other countries have different advice for the public and their positions have changed as the pandemic has progressed, usually as part of lockdown exit strategies. Some examples:

USA

The Centers for Disease Control and Prevention has recommended that public use of cloth face covers can be useful. This is in contexts where social distancing is difficult to maintain (such as grocery shopping), particularly in areas where community transmission is significant. The CDC states that medical masks should not be used by the public, as this would interfere with supplies for healthcare settings. The Surgeon General has appeared in a video giving advice on how to fashion a mask from textiles available in the home. There is no research evidence on the use of such masks in community settings.

France

Information on the government website states there is no evidence to support public use of paper masks, and there is no evidence that scarves used as masks are effective, because the weave of textiles allows the virus to pass through. A recent announcement recommends the use of masks by the public and mandates their use on public transport from 11 May. The State has stockpiled 20 million washable masks for the public.

Germany

On 21 April the government recommended that cloth masks be used in contexts where social distancing is difficult (shopping and using public transport). In some federal states and local authority areas it is mandatory.

This article will be updated as the research progresses.


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