How could wearing a mask reduce COVID-19 transmission?

Theoretically, wearing a mask can help reduce transmission in two ways:

  • Masks may reduce the amount of respiratory particles entering the environment through coughing, sneezing, speaking, and breathing by trapping them in the mask (‘source control’). Respiratory particles can contain the SARS-CoV-2 virus. Therefore, reducing the amount of particles emitted by people infected with SARS-CoV-2 may reduce exposure risks for healthy individuals. Since asymptomatic and pre-symptomatic individuals can still spread the SARS-CoV-2 virus, mask use by ‘healthy’ people (people without COVID-19 symptoms) may be important in reducing exposure risks to others.

  • Masks may offer some level of protection against personal exposure by preventing some respiratory particles from reaching your nose or mouth. The level of protection is dependent on the type of mask (or respirator) used (see this section for more info on mask types).

While both mechanisms may help prevent virus transmission, the primary benefit from the universal community-level use of masks is the reduction in the amount of SARS-CoV-2 entering the environment (‘source control’). See the below infographic which illustrates how masks may help reduce pathogen transmission via airborne particles.

Source: Science

What types of masks are there and what are they designed to do?

There are 4 main types of masks or respirators that are being discussed in relation to coronavirus. Masks (and respirators) are often rated by their filtration efficiency. Generally, filtration efficiency refers to the ability of a mask or material to filter out or block particles from passing through the mask. Filtration efficiency is typically presented as a percentage with higher numbers representing better performance. Filtration efficiency may vary by particle size and masks or respirators may be tested against a range of sizes to assess their ability to filter both small and large particles. Filtration efficiency is typically not based on a mask or respirator’s ability to filter out a particular pathogen but rather is based on filtration of generic, machine generated particles (typically made of salt solution). A summary of masks and respirators, with links to further information, is available below.

Summary of types of masks and respirators

To find out more about N95 respirators, surgical masks, fabric masks and occupational masks see the other sections within our resources.

The CDC highlights the differences and similarities of N95 respirators and surgical masks in the graphic below:

What is a N95 respirator and who should use one?

N95 respirators are a version of filtering facepiece respirators (FFR) worn by frontline health staff responding to the coronavirus and it is critical that they are prioritised for healthcare workers. N95 respirators fit closely to a person’s face and are very efficient at filtering small airborne particles such as this COVID-19 strain of coronavirus. In fact, N95 respirators are rated to filter out 95% of airborne particles (standard NIOSH 42 CFR Part 84). Prior to use, N95 respirators require a special fitting procedure to ensure they are effective. Due to their special fit requirements, N95 respirators cannot be used by children or persons with facial hair. If your organisation is purchasing N95 or other FFRs for use in healthcare settings it is important to make sure that these are produced to required standards and that you are aware of the performance characteristics of the product (i.e. how well the respirator filters out particles of a certain size range, or ‘filtration efficiency’). Typically, the higher (or better) the filtration efficiency, the more protective the respirator should be against SARS-CoV-2. A list of FFRs approved for use by the CDC is available here and an infographic outlining required labeling of CDC approved FFRs is available here. Some FFRs come with an exhalation valve. This is a small plastic device that can be seen on the outside of the respirator. This exhalation valve makes breathing more comfortable while wearing the respirator. The one-way valve means that the respirator allows exhalation of respiratory particles and will therefore be less effective in limiting onward transmission of SARS-CoV-2. The CDC recommends that N95 respirators with exhalation valves should not be used in healthcare settings and the European Centre for Disease Prevention and Control have made similar recommendations for them not to be used in communities either. N95 respirators are typically designated for ‘one time use’ only, however, global shortages have resulted in renewed interest in the safe decontamination of N95 respirators. A summary of decontamination procedures can be found in the annex of this WHO document on the rational use of personal protective equipment.

Who should wear a N95 respirator?

The use of FFRs or N95 respirators by the general public is not recommended. These respirators must be reserved for use by healthcare workers and require special fitting procedures to be effective. WHO guidance on the use of respirators and masks in the context of COVID-19 is available here.

What is a surgical mask and who should use one?

These are used in general practice among health staff. They are looser fitting than N95 respirators and disposable. They are designed to trap the user’s respiratory particles, created during coughing, sneezing, or speaking and prevent these particles from entering the environment. They also block large-particle droplets, splashes, sprays, or splatter that may contain germs (viruses and bacteria) from reaching the user’s mouth and nose. Some surgical masks will also block small particles (particles that are 0.1 micron in size), but this applies only to surgical masks manufactured to ASTM F2100 standards. While there are different types of surgical masks, with different degrees of thickness, most are not specifically designed to block the transmission of viruses via small airborne particles. Surgical masks are designed to balance filtration, breathability, and fluid penetration; their performance is tested by specific standardized methods (ASTM F2100, EN 14683). Surgical masks cannot safely be used more than once.

Who should wear a surgical mask?

The use of surgical masks is only recommended under limited circumstances. The World Health Organisation currently recommends that surgical masks are used by the following individuals:

  • If you have any symptoms associated with COVID-19

  • If you are taking care of or live with a person who is suspected to have COVID-19.

  • If you are working in a health centre or hospital and are in contact with people who could be infected with COVID-19.

  • If you are aged 60 or older or have pre-existing medical conditions

People with symptoms are asked to wear surgical masks so that they have a reduced likelihood of transmitting the virus to others. It is also recommended that people in caretaking roles wear masks because they are at high risk of infection. Watch this video from the WHO for more information on who should use surgical masks and how to put them on, wear them, and take them off safely. These guidelines on who should wear masks have been adopted by most national governments but there are some exceptions and variations. Please check mask-related guidelines with the National Department of Health in your country. Please see this resource for further information on the hygienic use of surgical masks and this resource for information on safe disposal.

What is a fabric mask, who should use one, and how should they be made?

Fabric masks include a wide range of designs and materials but generally includes any kind of mask that is made from fabric or cloth (including scarves or other fabric that is wrapped around a person’s face covering their mouth and nose) or non-woven material (e.g. polypropylene, polyethylene, or cellulose, materials generally used in surgical masks). These are typically worn by the general population due to concerns around infection or pollution. These masks are not recommended for use by medical personnel as the holes in the fabric are large enough for viruses like SARS-CoV-2 to pass through. Fabric mask design varies widely in material, shape, and number of layers, which can affect performance characteristics. The French Standardization Association has developed a set of standards outlining minimum performance of fabric masks for filtration and breathability (blocks 70% of droplets and solid particles). This video from the WHO summarizes guidance on when to wear fabric masks, design features of fabric masks, and considerations for the safe and hygienic use of fabric masks.

Who should wear fabric face masks?

The WHO recommends that decisions regarding public masking (fabric masks or surgical masks if they are not in short supply) be made using a risk-based approach that considers the following factors:

  • Purpose of the mask: Is the mask intended to provide personal protection against contracting COVID-19 or is the mask used for ‘source control’ purposes (i.e. to prevent infected persons, particularly those who are asymptomatic, from transmitting COVID-19 to others by limiting the spread of potentially infectious respiratory particles from the nose and mouth). Fabric face masks may not provide high-level protection to the wearer against COVID-19 but can help contribute to ‘source control’.

  • Risk of exposure: This requires considering the prevalence of COVID-19 among the local population and the characteristics of transmission (for example, is the region experiencing small clusters of cases or widespread community transmission). Individual-specific risks based on lifestyles or employment need to be considered. For example, WHO notes that community health workers may have higher risk of exposure, or of exposing others, due to their frequent interaction with the public. Hygiene Promotion staff may be in a similar position. Fabric face masks could be recommended for these high-risk groups or in case of widespread community transmission.

  • Vulnerability of the local population and the individual to severe disease: Are certain known risk factors for COVID-19 common among certain populations (e.g. diabetes, cardiovascular disease, age).

  • Setting: In certain areas and circumstances it may be difficult to physically distance. In densely populated areas like slums or camp settings physical distancing may be difficult. Similarly, it may be more difficult to adhere to physical distancing recommendations in enclosed settings such as on public transportation. In the USA, the CDC has recommended that fabric face masks be worn by the general public when outside home, emphasizing the importance of face masks in situations where other public health precautions, such as physical distancing, are difficult (e.g. grocery stores). Other countries have adopted similar guidelines regarding the use of face masks in all or some community and public settings.

  • Feasibility: Availability and cost of masks should be considered as that may limit access in certain settings. However, the US CDC has described ways to use common household items like t-shirts and bandanas to create fabric face masks. See here (Instructions for making fabric masks section). The availability of clean water and soap to wash fabric masks should also be considered.

The WHO provides a table of example scenarios where they apply their risk-based approach and indicate how to decide when surgical or fabric masks should be worn, by whom, and for what purpose. This video also summarizes WHO’s advice regarding the use of surgical and fabric masks. The pro-mask advocacy site MASKS4ALL documents country-level guidelines and recommendations for mask use.

For information on fabric mask use recommendations for children (defined as persons less than 18 years old), please see this section. To learn about safe and hygienic use of fabric face masks, please see this section. For our recommendations on the use of fabric masks for hygiene promoters please see this section. For information on why the WHO doesn’t recommend universal masking in all public spaces, please see this section.

Mask use should be combined with other measures like proper hand hygiene and physical distancing. Masks alone are not sufficient to prevent infection or reduce transmission.

What should be considered when making or purchasing fabric masks?

Both fabric choice and mask design can impact the effectiveness and wearability of masks.

Mask effectiveness is often measured as filtration efficiency which represents the percent of particles (usually within a defined size range) that are expected to be blocked by the mask. Masks made of fabrics with higher filtration efficiencies mean more particles are blocked and therefore may offer better protection to you and others.

Wearability relates to the ease of breathing in the mask and is usually reported as the difference in pressures measured on each side of the mask (often reported as ‘pressure drop’ in millibars or Pascals across the whole mask or per area, e.g. Pa/mask or mbar/centimeter2). Masks with large pressure differences would make breathing more difficult. The WHO recommends the pressure difference across the whole mask should be < 100 Pascals. For hygiene promoters, masks can be tested before field use by wearing them around the house during daily activities to make sure they offer adequate breathability.

When selecting or making a fabric mask, it is important to consider the following characteristics which will impact filtration efficiency and breathability:

Number of layers: Masks should be made of multiple layers of material. Masks made out of multiple layers of fabric or material often have improved filtration efficiency compared with single-layer masks. The WHO recommends a minimum of three layers for most fabric masks - described in this video. Ideally, the mask should consist of an inner layer made of an absorbent material (e.g. cotton or cotton blend), an outer layer made of water resistant material (polyester blends, polypropylene), and a middle layer either made of natural or synthetics materials. For commonly used fabrics (e.g. polyester, nylon, cotton), filtration efficiency may increase by up to 2-5 times when using two layers of a instead of one, or 2-7 times when using four layers (WHO, Study 1, Study 2). The following graph illustrates how filtration efficiency increases with the number of layers.

Data source: ACS Nano, 2020 ; Data visualization: Mona Chalabi

The video below, based on a single case study, illustrates how 1- and 2-layer fabric masks block the release of respiratory droplets and aerosols during speaking, coughing, and sneezing compared with wearing no mask or a surgical mask.

The gains in filtration efficiency achieved by using masks with multiple layers will depend on the type of fabric used as well as the number of layers used. For example, the filtration efficiency of a mask made of loose weave cotton (80 TPI) increased by four times when using 2 layers instead of one. In contrast, when using a tightly woven cotton fabric (600 TPI), the gain in filtration efficiency was negligible when using two versus one layer of fabric (Study 1).

Choice of fabric: Different materials and fabric weaves have different filtration efficiencies and therefore some materials are better suited for constructing fabric masks (Study 1, Study 2). Fabrics with tighter weaves may offer better filtration, particularly for small particles, but may impact breathability. For example, the filtration efficiency of cotton fabrics with tighter weaves (600 threads per inch [TPI]) was almost 9 times higher than cotton with looser weaves (80 threads per inch). Cotton, polyester and blends can all be used, as well as materials usually found in surgical masks (like polypropylene). Avoid using materials with very loose weaves (e.g. gauze) or stretchy materials which may distort the weave and impair filtration. Materials with visible pores when held up to a light source should be avoided or used only as part of a multilayer mask.

Combining materials: Hybrid masks that combine different materials such as cotton with silk, or polyester blends, have been shown to increase filtration efficiency. The different fabrics of the hybrid masks may work together to allow effective filtration of a range of particle sizes.

Fit: Masks come in a variety of acceptable shapes (flat-fold, duckbilled, molded, etc). Fit is more important than shape. The mask should fit closely around the nose, cheeks, and chin. Poor fit can reduce the performance characteristics of the mask. Unfiltered air may enter or exit the mask at gaps created by poorly fit masks. If you feel lots of air exiting around the edges of the mask then this is an indication that the fit is poor.

Exhalation valves: Some commercially available fabric masks include exhalation or one-way valves that are meant to make it easier to breathe. Masks with such valves are not recommended as they allow the user to expel respiratory secretions and limit the function of the mask for source control.

Several online resources provide simple step-by-step instructions for making your own fabric face mask. The CDC provides instructions for making three simple masks at home. A video demonstrating the third option is available here in English and here in Spanish. The WHO has also made a video on sewing tips for making fabric face masks. Fabric face masks are also widely available for purchase from online retailers but do consider the mask characteristics described above before purchasing them.

In some countries community groups are also producing masks which are more inclusive. These masks have a clear plastic window at the front of the mask allowing people with hearing impairments and who rely on lip reading, to more easily communicate at this time. As with many homemade fabric masks, the safety of most of these masks has not been tested but they are being encouraged by support groups for people with hearing impairments. Surgical masks with similar adaptations are approved for use in healthcare settings in the USA. Ensure any mask modifications such as these do not increase the likelihood for exhaled air to escape the sides of the masks.

What is an occupational mask and who should wear one?

In some settings masks manufactured for purposes such as construction or manufacturing are available. These masks are often described as reusable half-face masks, reusable full face masks or dust filtration masks and are designed for preventing the transmission of chemicals, solvents, dust and other particles. They normally have filters that are attached on the side which are replaceable. Some of these masks are effective for use against SARS-CoV-2 but use of these masks in healthcare settings should always be verified by the manufacturer and national guidelines. The use of these types of masks is not recommended in community settings because they are not available at scale, they are visually quite scary looking and may create unnecessary fear, and because they are produced at a range of qualities.

Safe use of fabric and surgical masks

Hygienic use of fabric face masks

Fabric face masks should only be used if hygienic use conditions are applied. This video and the below infographic from the WHO summarizes how to safely wear a fabric face mask. Hygienic use includes daily washing or decontamination. Fabric masks should be machine or hand washed in hot soapy water (water should be at least 60 degrees centigrade or as hot as permitted by the fabric) with standard laundry detergent and fully dried before reuse (a machine dryer is preferable). If a machine washer or hot water is not available, the WHO and CDC recommend soaking fabric masks in a dilute chlorine solution (0.1% chlorine, 1 part household bleach [typically 5% chlorine] to 49 parts water) for 1-5 minutes before rinsing and drying or boiling for 1 minute. Note that bleach may discolor some fabrics.

The safe and hygienic use of fabric masks among hygiene promoters is described in this section.

Safe use of surgical masks

If surgical masks are being used outside of healthcare settings then it is important that community members are well informed about how to wear, handle and dispose of surgical masks. For guidance on the safe use of surgical masks, please watch this video or see the below infographic from the WHO. Please see this resource for more information on how to safely dispose of used surgical masks.

Why doesn’t the WHO recommend that everyone wears face masks in all settings?

There are a range of reasons why mask wearing has not been recommended by the WHO for the general public. These are explained below.

False sense of protection - Wearing masks is not normal for most people. Putting one on can give people a false sense of protection against the virus and may make them less likely to practice other key preventative behaviours such as handwashing with soap and physical distancing. However in some settings mask-use has been found to be associated with other positive hygiene measures.

Potential self-contamination - Improper mask use (and re-use) could pose an infection risk if they become contaminated and proper hand hygiene is not followed. Surgical masks and N95 respirators are in short supply globally and so at the moment lots of people are buying and reusing them for extended periods of time or over the course of multiple days. Not changing masks when they become wet or soiled could allow bacteria to grow.

Prioritising masks for those who need them most - The demand for surgical masks and N95 respirators has increased dramatically with the spread of COVID-19 and the WHO and governments around the world are struggling to meet this supply. It is critical that public use of these items does not prevent them being available to those who need them most.

Mask use tends to be sporadic - Studies among people at risk of infection have shown that people do not wear masks consistently, limiting their benefit. However, recent studies in Hong Kong demonstrated that residents believed masks to be protective and that mask use in public spaces increased over the course of the outbreak.

Mixed evidence on effectiveness for public protection - The evidence we have about the benefits and limitations of masks are largely drawn from studies on influenza, studies in healthcare facilities, and studies of surgical masks or respirators, so it is hard to know how applicable they are to this pandemic. For more information, see ‘What do we know about the effectiveness of masks to prevent COVID-19 transmission in community settings?’.

Improper disposal - Littering of masks or respirators could pose contamination risks for waste management workers or others who come into contact with them.

Difficulties related to wearing masks - People with hearing impairments may struggle to communicate if they rely on lip reading (see our section on inclusive fabric masks). Mask wearing may be difficult for other sub-groups of the population including children, people with cognitive or intellectual disabilities, people with respiratory problems (unrelated to COVID-19) or those living in hot and humid environments.

Mixed evidence about mode of transmission - Most COVID-19 infections are a result of being in close contact with an infectious person (for example, living with an infected person). At present, the WHO does not currently consider airborne transmission via aerosols to be a main route of transmission for SARS-CoV-2 among the general population but has recently acknowledged that it cannot be ruled out in crowded indoor settings with poor ventilation. While the possibility of airborne transmission is possible and may occur in some settings, the WHO maintains that COVID-19 is largely spread via large droplets emitted by infected individuals into the air. What they mean by this is that transmission occurs when an infected person coughs, sneezes or speaks and then releases large droplets into the air around them. These droplets are heavier than the air around them so they tend to fall on floors, surfaces or people in the surrounding area. For airborne transmission to occur, a virus must be suspended in smaller, lighter droplets (also termed ‘aerosols’) that can remain in the air for some time (e.g. even after the infected individual has left the room).

There is currently limited evidence as to whether airborne transmission of SARS-CoV-2 is occurring and to what extent, but it appears plausible and the idea is supported by a group of multidisciplinary scientists and engineers. Humans may expel aerosols during coughing and sneezing as well as normal speaking and breathing and some larger droplets expelled may evaporate to form smaller, lighter aerosols which can remain airborne for longer. Different sized particles may reach different areas of the lungs when inhaled, with smaller particles having greater potential to penetrate the lower respiratory tract. For such aerosols to cause COVID-19, expelled particles and aerosols must contain infectious SARS-CoV-2 particles. Experimental studies have demonstrated that infectious SARS-CoV-2 can remain in the airborne for at least 3 hours and potentially up to 16 hours in laboratory-generated aerosols. While useful to understand the potential for airborne transmission, the results of laboratory-based studies must be interpreted with caution because they do not reflect real-life circumstances and laboratory-generated aerosols may not be representative of the pattern of aerosols expelled during coughing, speaking, or breathing. Evidence of SARS-CoV-2 in air samples from healthcare and community settings is mixed and limited. Several studies have detected low concentrations of SARS-CoV-2 genetic material in air samples taken from hospital settings (Study 1, Study 2, Study 3, Study 4), while others have been unable to detect SARS-CoV-2 in air samples from patient hospital rooms (Study 1, Study 2, Study 3, Study 4). To date, only a single unpublished study has detected low levels of infectious virus in air samples collected from hospital rooms of COVID-19 patients. It is unclear if the level of virus detected is high enough to cause infection. There is an important distinction between the detection of genetic material, which can persist after a virus has been inactivated (‘killed’) and viable (‘live’) virus which may be capable of causing infection. To understand this further read this resource. Additional reviews summarizing the evidence of airborne transmission for SARS-CoV-2 are available here and here.

What do we know about the effectiveness of masks to prevent COVID-19 transmission in community settings?

Most studies of the effectiveness of masks to interrupt disease transmission have focused on prevention of other, non-COVID-19 respiratory diseases, mask use in healthcare settings, and the use of respirators (N95) or surgical masks. There is limited evidence that applies specifically to the question of whether fabric mask use by the general public could limit the transmission of SARS-CoV-2.

A recent systematic review of mask use was published in the Lancet and found that wearing a mask in both healthcare and community settings reduced the risk of infection with coronaviruses that cause COVID-19, SARS, or MERS. However, few studies of COVID-19 in non-healthcare (community settings) were available and none were included in the final meta-analysis assessing mask use in community settings. The authors found that mask-wearing was more protective in healthcare facilities than in community settings. This could be because healthcare workers have increased exposure or because N95 respirators are more common in healthcare settings and were found to be more effective than surgical masks or multi-layer fabric masks in preventing infection. It could also be because healthcare staff are more likely to adhere to correct procedures for the safe and effective use of masks. Further, N95 respirators, surgical masks, and multi-layer fabric masks were found to be more protective than single-layer masks. However, the authors suggested that additional, higher quality evidence is needed as all studies included in this review were observational.

A recent retrospective cohort study in China found that if household members wore masks prior to a member becoming noticeably ill with COVID-19, the risk of COVID-19 transmission to healthy family members was reduced.

There are several recent systematic reviews and meta-analyses that have evaluated the impact of mask-wearing on respiratory infection in both healthcare and community settings (Study 1, Study 2, unpublished Study 3, unpublished Study 4, unpublished Study 5). All of these reviews found that there were no available or eligible studies on the impact of fabric face masks on COVID-19 transmission in community settings. Two of these reviews suggest that masks may be protective in community settings (Study 1, unpublished Study 3). One review found some evidence of protective effects for self-reported illness but no effect on laboratory-confirmed illness, and two found limited evidence of a protective effect of surgical masks (Study 2, unpublished Study 4). The strength of evidence varied by study design and outcome definition, complicating the interpretation. All reviews agreed that their analyses were limited by substantial evidence gaps and issues with study quality. Even given limited evidence, the authors of four of the five reviews promoted the use of masks by the public, alongside other preventative measures such as physical distancing and hand hygiene, in at least some community settings.

What can modelling studies tell us about the effectiveness of wearing masks?

Modelling studies are studies that use evidence-based assumptions and statistics to predict what might happen to populations and disease transmission patterns. Given the limited empirical data around mask use and COVID-19 transmission, modelling studies can aid our understanding of the potential effect masks may have on COVID-19 transmission.

Modelling studies have suggested that surgical mask use is likely to be effective in reducing the rate of infection with COVID-19 (Study 1, Study 2, Study 3, Study 4, Study 5) or other respiratory diseases, particularly when combined with other non-pharmaceutical interventions like physical distancing and hand hygiene. In one modelling study, even low or moderately effective masks could have substantial impacts on transmission of COVID-19 in some settings. Another study showed that high adherence of surgical mask use (80%) could effectively eliminate an outbreak of influenza. The Institute of Health Metrics and Evaluation’s COVID-19 transmission model dashboard illustrates how universal mask use may impact COVID-19 outcomes in different settings. Results of models should always be interpreted with caution as results can be sensitive to the model assumptions and parameters. For example, models that predict influenza transmission may not be directly applicable to the current COVID-19 pandemic.

How well do masks work under laboratory (experimental) conditions?

Experimental studies normally take place in a laboratory and are designed to simulate and test certain real-world conditions in a safe way.

Several experimental studies have simulated the effectiveness of various mask types to a) stop an infectious person spreading respiratory virus (‘source control’) and b) prevent a healthy person from getting a respiratory virus. A recent study found surgical masks could effectively reduce the emission of coronaviruses and influenza viruses from infected patients, potentially limiting onward transmission. Another study found that N95 respirators, surgical masks, and fabric masks (made from tea towels) all reduced exposure during various activities and that the effectiveness of masks did not decrease over a three-hour period. However, in simulated human breath experiments, fabric masks had minimal effect on limiting emission of respiratory particles. A study comparing surgical masks, homemade cotton t-shirt masks, and no masks found that both surgical masks and fabric masks reduced the number of microorganisms released during coughing. While both offered some protection, the surgical masks were more effective in filtering microorganisms, potentially because the homemade masks did not achieve as close of a fit as surgical masks.

Past studies of fabric mask filtration efficiency have found different fabrics are capable of reducing particle emission between 10-97% depending on the size of the particle and the fabric and design (number of layers) of the masks. A recent study examined the filtration efficiency of several common types of fabric, used in single or multiple layers, and used in combination with other fabric types (‘hybrids’), to prevent the emission of particles in two size ranges (<0.3 microns and 3-6 microns). Filtration efficiency varied between 9 - 99% depending on mask design and fabric and particle size range. Hybrid masks that contained high-thread count cotton combined with silk, chiffon or flannel, were among the most efficient at filtering out particles of both size ranges. Masks with multiple layers of chiffon, high-thread count cotton, and silk were also effective in filtering particles of both sizes.

When interpreting lab-based studies, remember that experimental conditions may not always replicate real-world conditions. For example, filtration efficiency is not typically assessed for individual pathogens like SARS-CoV-2. Instead, reported filtration efficiency is often based on the ability of a fabric mask to filter out different sized particles (or pathogen surrogates in some studies). This is partly why there is little data on the efficacy of fabric masks for SARS-CoV-2 specifically. Further, the generation of aerosols in the laboratory (often produced via equipment like a nebulizer) may not reflect the pattern or frequency of aerosol production during normal human speaking, singing, or coughing.

Do homemade masks increase the risk of respiratory disease?

A study of fabric masks in a hospital setting found that surgical masks performed better than fabric masks in preventing respiratory infection. This study also found that use of fabric masks resulted in higher risk of infection than ‘standard practice’. This result has been widely misinterpreted to mean fabric masks increase the risk of infection compared with not wearing a mask at all. This is incorrect because wearing fabric masks was compared to ‘standard practice’ which, in the study settings, included mask wearing in certain scenarios. Even so, fabric mask use is not recommended for healthcare settings.

However, proper mask use and hygiene is important. If masks are improperly used (touched during wear without proper hand hygiene, continued wear after becoming damp or soiled), there is a potential for self-contamination. Please see the section on hygienic mask use for further information.

How might an evolving understanding of virus transmission affect mask recommendations?

It is fair to say that there has been a lot of contradictory guidelines and information about the use of face masks at a community level. While the WHO are not currently encouraging the universal use of masks among healthy adults in all public settings, we have already seen several nations promoting or mandating the use of masks among the general population (e.g. USA, Czech Republic, China). See this map for a global view of current guidelines (compiled by a pro-mask advocacy group). It is possible that recommendations around masks will change in the coming weeks or months. Below we explain how new evidence may result in changes to recommendations.

Realisation that all citizens pose a risk for transmission - It is now understood that people who are not showing symptoms can still be carrying the virus and can transmit it. This poses a challenge for interrupting transmission as healthy individuals are less likely to take precautionary measures such as quarantining after potential contact with the virus or an infected person. Mask usage among the general population may therefore be considered beneficial for source control. The relative importance of transmission from asymptomatic or pre-symptomatic individuals, compared to transmission via symptomatic individuals, is unclear and still being investigated.

Further evidence around airborne transmission - If further evidence is found to demonstrate that transmission can occur via small airborne droplets (aerosols), mask use will be an important method of reducing transmission in public settings. The WHO does not currently consider airborne transmission via aerosols to be a main route of transmission for SARS-CoV-2 among the general population but has recently acknowledged that it cannot be ruled out in crowded indoor settings with poor ventilation. For more information on the evidence for airborne transmission, read the ‘Mixed evidence of modes of transmission’ section here.

Should hygiene promotion staff wear masks to protect themselves and others?

Summary of Mask Recommendations for Hygiene Promotion Staff

  • N95 respirators should be prioritised for health workers and hospital staff.

  • Surgical masks should be prioritised for symptomatic individuals, those caring for or in close proximity COVID-19 cases, and high risk individuals who may be more vulnerable to COVID-19 (people older than 60 years, people with pre-existing medical conditions).

  • Hygiene promoters do not fit into either of the above categories but are at higher risk than the general population and could put others at risk, especially in settings where physical distancing may be difficult.

  • Hygiene promoters should be encouraged to wear fabric masks if the hygienic use conditions described below can be met and maintained. If these hygienic use conditions cannot be maintained then fabric masks should not be used by hygiene promoters.

Below we describe the rationale behind each of these recommendations.

In some countries it is still safe for hygiene promotion staff to be going from household to household to share information about COVID-19 and promote hygiene behaviors. Hygiene promoters have a critical role to play in terms of interrupting transmission but this type of hygiene promotion is also a risk. As hygiene promoters move around communities they are putting themselves at a higher risk of getting infected. We also know that people infected with COVID-19 may be infectious (able to spread the virus) but not symptomatic (Study 1, Study 2, Study 3). This means that hygiene promoters who feel healthy may themselves be infected and at risk of spreading this to other people in the community.

Due to the potential risks of transmission during community hygiene promotion activities, we recommend hygiene promoters wear fabric masks if the conditions outlined below can be met and maintained. The purpose of wearing these masks is to prevent hygiene promoters from spreading the disease to others in the community (‘source protection’). Organisations should provide fabric masks to their staff (rather than relying on staff to make or purchase them), train them on their safe use, and provide zip-lock plastic bags for storing used masks prior to washing. Due to limited supplies, we do not currently recommend the use of N95 respirators or surgical masks, even though they may offer a higher level of protection, as these masks must be reserved for healthcare workers, caretakers of COVID-19 patients, vulnerable populations and those with symptoms.

Hygienic use conditions for fabric mask wearing among hygiene promoters:

  • Make masks out multiple layers of material. The WHO recommends masks be made of at least three layers. Choose materials and designs that balance breathability and filtration efficiency. Fabrics with tighter weaves are preferable over looser weaves (e.g. choose higher thread count cotton vs lower thread count) as they may offer better filtration. Consider combining layers of different fabric, including a water resistant outer layer (polyester blend, non-woven polypropylene) and a water absorbent inner layer (cotton). For more information see our section on What should be considered when making fabric masks.

  • Attach ties or elastic ear-loops at the top and base so that you can ensure a good fit.

  • Ensure a tight fit around the nose and mouth. Using a thin piece of wire at the top of the mask could aid in achieving this around the nose.

  • Wash your hands with soap and water or use alcohol-based hand rub prior to putting the mask on and after taking it off.

  • Ensure all hygiene promotion staff have multiple masks and that they can change them when damp, visibly soiled, or at least every day.

  • Do not touch masks during use. If accidental contact occurs, wash hands with soap and water or alcohol-based hand gel.

  • Remove masks from the back (ties or ear-loops) and avoid touching the front of the mask while removing (See the infographic below). Once removed, reusable fabric masks should be immediately washed or stored in a sealable plastic bag until they can be washed.

  • Machine or hand wash fabric masks in hot soapy water (water should be at least 60 degrees centigrade or as hot as permitted by the fabric) with standard laundry detergent and fully dry before reuse (a machine dryer is preferable). If a machine washer is not available, the WHO and CDC recommend soaking fabric masks in a dilute chlorine solution (0.1% chlorine, 1 part household bleach [typically 5% chlorine] to 49 parts water) for 1-5 minutes before rinsing and drying or boiling for 1 minute. Note that bleach may discolour some fabrics. We recommend demonstrating the cleaning process to hygiene promotion staff prior to recommending use.

  • Masks should not be shared among hygiene promoters.

Additional information on the safe and hygienic use of fabric masks is summarized in this section and this WHO video.

If your organisation decides to promote fabric masks among your hygiene promoters in a region where mask-wearing by the general public has not been recommended, you need to make sure that your staff are able to explain why they are wearing masks and why masks are not encouraged for the rest of the population. For tips on discussing COVID-19 transmission and mask-wearing without using stigmatizing language, see this Oxfam guidance.

Note: If supply systems of surgical masks are able to adapt to the current need and there is ample supply in your setting, then hygiene promoters should switch to these rather than fabric masks. Handwashing and safe use and disposal will still be key to practice. Please see this section for additional information on the safe disposal of personal protective equipment, including surgical masks.

Should children wear fabric masks in community settings?

Evidence of transmission and mask use among children

Children, defined here as anyone less than 18 years old, can be infected with SARS-CoV-2 and transmit it to others. Between 1 - 7% of confirmed COVID-19 cases have been reported among children (Study 1, Study 2, Study 3, Study 4). As children tend to have less severe COVID-19 symptoms than adults, case-based reports of COVID-19 may underestimate the true prevalence of infection among children. The amount and duration of SARS-CoV-2 shedding among children is incompletely characterised with several studies reporting differing results (Study 1, Study 2, unpublished study 3). The effect of age on transmission, and therefore the contribution of children to global COVID-19 transmission, is not well understood.

Currently, there are no studies of the effectiveness of mask use among children in limiting COVID-19 transmission. There is limited evidence that mask use may reduce influenza transmission among school-aged children, particularly when used soon after symptom onset, though other studies have found no effect. Mask effectiveness may be influenced by acceptability and consistent use which have been shown to be highly variable among children (Study 1, Study 2, Study 3, Study 4, Study 5). Factors such as age, duration of use, and discomfort may impact acceptability and use.

Recommendations for fabric mask use among children in community settings

Given the limited available evidence on the effectiveness of masks to reduce or prevent transmission of COVID-19 among children, the WHO suggests that mask use policies be driven by three “overarching guiding principles”:

  • Do no harm. Prioritize the health, well-being, and best interests of children.

  • Avoid policies that may have a negative impact on development or learning outcomes.

  • Policies should consider the feasibility of implementation in different contexts, including consideration of social, cultural, and geographics norms, availability of resources, setting type (e.g. humanitarian), and special needs groups (e.g. those with disabilities or specific health conditions).

In areas where community transmission is ongoing and physical distancing is difficult, the WHO has provided the following recommendations regarding mask use among children:

  1. Children aged five years or younger should not wear masks for source control. If national policy dictates that children younger than five are required to wear masks, the WHO recommends that those children are under constant supervision to ensure child safety and proper mask use. Under no circumstances should children younger than five with severe cognitive or respiratory challenges be required to wear masks.

  2. A risk-based approach should be used to decide whether children aged six to 11 years of age should wear masks. The approach should consider the following: (1) the amount of community transmission in the area and any newly available evidence on risk of transmission among children aged 6 - 11 years; (2) any social and cultural beliefs, customs, behaviors or other norms that influence interactions with and among children; (3) the child’s ability to appropriately use the mask and the availability of adult supervision; (4) the potential implications of mask wearing on learning and psychosocial development; and (5) adaptations for specific settings including schools, sporting events, or when there is potential for exposure to vulnerable populations such as the elderly or those with underlying disease or disability).

  3. Children aged 12 years or older should follow WHO or national guidance for mask use in adults. For these children, mask use may not be recommended in certain circumstances or settings, as described below.

  4. Decisions about mask use for children with certain health conditions, diseases, disabilities, or developmental disorders should be made in consultation with a medical provider. Mask use is typically recommended for children who are immunocompromised or have been diagnosed with cystic fibrosis or cancer. Mask use should not be mandatory for children with developmental disorders, disabilities, or other health conditions but rather be decided on a case by case basis.

Considerations for mask use in specific circumstances and settings

  • Children with disabilities or developmental disorders: Mask use should not be required for children with disabilities or developmental disorders. These children should be given alternative options such as wearing face shields. Adults working with children with disabilities who require close physical contact should wear masks and adhere to other infection prevention and control measures such as frequent hand hygiene. Widespread mask use, coupled with physical distancing, may pose challenges for children with hearing problems who rely on lipreading or facial expressions to communicate. In these cases, families, educators, and others may consider using face shields or masks with clear panels to allow for lipreading. The below photo depicts a fabric mask with a clear panel in front.

Source: Jakarta Post

  • Mask use in schools: School mask policies should consider a) the age-related WHO recommendations for mask use among children, b) how the mask policy fits within a broader infection prevention and control strategy (e.g. hand hygiene, physical distancing), and c) the thoughts of educators who may have to balance the advantages of mask use against its potential burden on learning and other school activities. For additional information on the use of masks in schools please see this resource ‘Promoting good respiratory hygiene practices’.

Implementation Considerations for Child Mask Use Policy

Communication: Communication materials explaining the purpose and use of masks should be adapted to be context-specific and age-appropriate for children and should remain flexible to changes in evidence, community needs, and feedback or questions from children. Parents/guardians, educators, and trusted community members and leaders should communicate the importance and safe use of masks to children through role-modelling. Messaging to children should emphasize the role of masks as one part of a broader infection prevention and control strategy to ensure mask use does not result in children feeling a false sense of security and disregarding other preventative measures.

Mask design and use: Mask design should consider the quality, breathability, fit, and comfort of the child. As acceptability among children may be a barrier to use, masks should be child-friendly and be made in a variety of sizes, colours and designs. For more information on the design features of fabric masks, please see this resource. Strategies to assist children in the safe use of masks should be considered. This includes providing for the safe storage of used masks for reuse (e.g. following eating, exercise) or for eventual laundering. Children may require use of several masks over the course of a day as they become soiled, wet, or lost.

Accessibility: Ensuring equitable access to masks among children is important and access must not be a barrier to use. Masks should be accessible free of charge to children living in limited resource settings.

Alternatives to masks: Some children may have difficulty wearing a mask due to disabilities, health issues, or other reasons. The WHO suggests the use of face shields in these circumstances. Face shields may provide some protection from respiratory droplets, though large gaps between the shield and face may limit effectiveness. There is currently no evidence on the use of face shields for source control. For these reasons, face shields should not be considered equivalent to masks in terms of protection or source control but they are suggested as an alternative for children who may not be able to wear masks. If face shields are to be used, the following precautions and use instructions should be implemented:

  • As face shields offer only partial protection, physical distancing, hand hygiene, and other infection prevention and control strategies remain important.

  • The face shield should wrap around the sides of the face and extend below the chin.

  • Face shields should be cleaned with soap and water and disinfected with ≥70% ethanol after each use.

  • Children should be instructed on how to safely put on, take off, and wear face shields to avoid injury during use.

Monitoring and evaluation: Given limited evidence of face mask use among children, the WHO recommends setting up monitoring and evaluation programs to assess the impact of masks on child physical and mental health. Key indicators should include impact on COVID-19 transmission, acceptability, use, and barriers of mask use, and potential effects on learning, development, and school attendance. The impact on children with special needs should be given specific attention. For more information on monitoring evaluation, please see this WHO document.

What protection measures can our hygiene promoters take to stay safe when working in communities?

Hygiene promoters can play an important role in promoting physical distancing measures. Here are a few simple ways they can do this during household visits or in their community. Make sure that they explain why they are doing these measures so that they are still welcome and acting in ways that are socially acceptable. Hygiene promoters should always:

  • Avoid handshaking

  • Avoid all forms of physical contact

  • Observe physical distancing by standing 1 to 2 meters away from others (depending on national guidelines)

  • Wash their hands frequently, preferably on arrival to each house. Where possible give hygiene promoters alcohol based hand rub to take with them. Otherwise hygiene promoters should wash hands with soap at public facilities or at household facilities that are outside. If this can not be maintained at sufficient frequency then consider doing remote forms of hygiene promotion and community engagement.

  • All household visits should be done outside of the house. Hygiene promoters should not enter homes and should avoid using spaces that are enclosed, poorly ventilated or indoors.

For guidance on whether hygiene promoters should wear gloves see this article. For other examples of how hygiene promoters can keep themselves and communities safe while doing in-person work, see the resources below:

Editor's note

Author: Jackie Knee
Review: Peter Winch, Julie Watson
Last update: 10.09.2020

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