How well do cloth masks reduce transmission of SARS-CoV-2 viral particles?

Summary

The following is a summary of evidence sources that provide high quality information on how well cloth masks reduce transmission of SARS-CoV-2 viral particles. For additional information about each of the sources, see the Table below.

Three systematic reviews have concluded that, compared to no mask use at all, cloth masks reduce the risk of virus transmission by providing a barrier against droplets to reduce contamination of air and surfaces [1,2,4,9]. In its About Cloth Face Coverings guidance, the Centers for Disease Control and Prevent (CDC) recommends cloth mask use in the community to possibly prevent the spread of virus from the wearer to others [7]. The authors of two reviews investigating the efficacy of face masks against coronaviruses and other respiratory transmissible viruses state that community use of masks could be beneficial, particularly for COVID-19, where transmission may be due to dissemination from pre-symptomatic, asymptomatic, and mildly symptomatic individuals [3,8]. However, masks are most effective when used alongside hand hygiene and other preventative measures including social distancing [1,3,8].

The authors on a systematic review of the Utility of Cloth Masks in Preventing Respiratory Infections, found that the material with which a mask is constructed can greatly affect its filtration efficacy [4]. Leakage from a mask can also reduce efficacy by about 50% [4]. The authors of this systematic review as well as Alberta Health Services call for better guidance on optimal mask construction and standardization of cloth masks [4, 5]. The World Health Organization (WHO) states in its Advice on the use of masks in the context of COVID-19, that two-layered masks provide 2-5 times improved filtration efficiency compared to a single-layered mask, however acknowledges that few mask materials and layer combinations have been systematically evaluated [6]. The WHO recommends a mask constructed of three layers for optimal efficiency: 1) an innermost layer of a hydrophilic material (e.g. cotton or cotton blend), 2) an outermost layer made of a hydrophobic material (e.g. polypropylene, polyester or their blends), and 3) a middle hydrophobic layer of synthetic non-woven material which may enhance filtration or retain droplets (e.g. polypropylene or cotton layer) [6]. The CDC recommends that masks with an exhalation valves, gaiters or face shields should be avoided as they allow virus particles to escape [7].

Two systematic reviews conclude that cloth masks are not recommended for use among healthcare workers [3,4]. As compared to cloth masks and single-layer masks, both N95 and surgical masks have been found to have greater filtration efficacy [3,4].

Evidence

What‘s Trending on Social Media and Media

Multiple YouTube videos have surfaced and are currently trending instructing individuals on how to best sew and create the most effective two-layered cloth mask.

A viral video of a “breathe test” has circulated of a Filipina Doctor, Dr. Leslee Anne Herrera breathing through masks and trying to blow a lighter identifying that this is an easy test to see if your medical/cloth mask is fully effective at preventing particles from coming in and going out of your mask.

The CDC has published easy to understand illustrations explaining how cloth face covering are effective in preventing spread of SARS-CoV-2. However, it is imperative that all individuals wear cloth masks, in order for containment of the virus to be most effective. Cloth masks are currently the most recommended face covering option, as it is still a top priority to save medical grade personal protective equipment for frontline workers.

Organizational Scan

The guidance provided by the Canadian and Ontario governments recommend non-medial face masks or homemade face coverings be worn by the public when physical distancing (2-metre distance) cannot be maintained, particularly in public settings, such as: stores, shopping areas, and public transportation [10,11].

The Public Health Ontario guidance suggests that a non-medical mask or face covering will protect others from infectious droplets. However, it is stated that non-medical masks and face coverings may not provide complete protection against viral particles, especially if they fit loosely. Public mask wearing is likely beneficial as a source of control when worn by a person shedding infectious virus [10].

The Canadian and Ontario governments and Centers for Disease Control and Prevention guidance documents provide a list of resources about non-medical face masks regarding how to properly make, wear, remove and clean the masks. The face mask should be made of at least two layers and fit securely to the head and be large enough to completely cover the nose and mouth without gaping [10,11]. Each cloth mask should be able to be laundered multiple times without losing shape or deteriorating [10]. When wearing the mask, avoid touching the covering and remove the mask by the ear loops. Wash hands immediately after using [10,11]. Cloth face masks can be cleaned by putting directly into the washing machine or washing by hand by placing in a bleach solution [12].

Numerous Ontario municipalities have approved a temporary bylaw to make non-medical face masks, which includes cloth masks, mandatory in all enclosed public places as of July 7th, 2020 to prevent the spread of COVID-19. Some municipalities include Toronto, York, Durham, Peel, Simcoe-Muskoka, Wellington-Dufferin-Guelph, Halton, etc.

Review of Evidence

Resource	Type/Source of Evidence	Last Updated
Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis — Chu et al.	Systematic Review	This review notes that transmission of viruses was lower with distancing of 1 metre or more and with decreased length of exposure. Face mask use could result is large reduction in risk of infection, with a stronger association with N95 masks, although an association with surgical or similar masks was still seen. Eye protection also was associated with less infection. Last Updated: June 26, 2020
Homemade cloth face masks as a barrier against respiratory droplets – systematic review — Taminato et al.	Systematic Review	This review notes that using a cloth face mask provides a barrier against droplets when compared with not using a face mask. The face mask should be used along with respiratory etiquette, hand hygiene, social distancing and isolation of cases. Last Updated: April 30, 2020
A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients — MacIntyre & Chughtai	Systematic Review	This review found that medical masks are more protective than cloth masks. When a cloth mask is used by sick patients it is suggested that there is protection for healthy contacts. Community mask use by well people could be beneficial, particularly for COVID-19, where transmission may be pre-symptomatic. In the community, masks appeared to be effective with and without hand hygiene, although both together were most effective. Cloth masks are not recommended for use among healthcare workers. Last Updated: April 29, 2020
Utility of Cloth Masks in Preventing Respiratory Infections: A Systematic Review — Mondal et al.	Systematic Review	This review found that cloth masks generally performed poorer than medical grade masks but were better than no masks at all. Filtration efficacy varied greatly dependent on what material was used. Some materials showed a filtration efficacy above 90%, while leakage could reduce efficacy of masks by about 50%. Standardization of cloth masks and appropriate use is essential for community masking. Cloth masking is ineffective in healthcare settings. The review notes that their analysis is limited by the lack of sufficient clinical studies and standardization between studies and cloth mask type. Last Updated: May 10, 2020
What is the effectiveness of wearing medical masks, including home-made masks, to reduce the spread of COVID-19 in the community? — Alberta Health Services	Rapid Review	Alberta Health Services notes that based on lab-based aerosol studies, medical masks appear superior to homemade cloth masks but optimally constructed homemade masks may offer some protection in reducing dispersion of droplets. Last Updated: June 18, 2020
Advice on the use of masks in the context of COVID-19 — WHO: World Health Organization	International Guidance	This report indicates that non-medical masks vary by the combinations of fabrics used, layering sequences and mask shapes. Few of these combinations have been systematically evaluated. When masks have two layers, the mask provides 2-5 times increased filtration efficiency compared to a single layered mask. The optimal combination of material for cloth masks should include three layers: 1) an innermost layer of a hydrophilic material (e.g. cotton or cotton blend); 2) an outermost layer made of a hydrophobic material (e.g. polypropylene, polyester or their blends); 3) a middle hydrophobic layer of synthetic non-woven material which may enhance filtration or retain droplets (e.g. polypropylene or cotton layer) Last Updated: June 4, 2020
About Cloth Face Coverings — CDC: Centers for Disease Control and Prevention	National Guidance	The CDC recommends that people wear cloth face coverings in community settings when around people outside of their household and when distancing measures are difficult to maintain. A cloth face covering may not protect the wearer but may keep the wearer from spreading the virus to others. Therefore, face coverings are most likely to reduce the spread of COVID-19 when they are widely used. Surgical masks and N95 respirators should be saved for healthcare workers and therefore not used in community settings. Masks that are made of fabric that makes it hard to breathe, for example, vinyl, and masks that have exhalation valves, that allow virus particles to escape, should be avoided. The CDC does not recommend the use of gaiters or face shields. Last Updated: August 26, 2020
Comprehensive review of mask utility and challenges during the covid-19 pandemic — Tirupathi et al.	Literature Review	Masks alone may not greatly slow the spread of COVID-19 and should be used alongside adequate social distancing, diligent hand hygiene and other preventative measures. Community mask use may be especially beneficial in reducing transmission due to the plausible dissemination of SARS-CoV-2 transmission from asymptomatic, pre-symptomatic and mildly symptomatic individuals. Last Updated: May 31, 2020
Cloth Masks May Prevent Transmission of COVID-19: An Evidence-Based, Risk-Based Approach — Clase et al.	Literature Review	This literature review notes that cloth masks reduce contamination of air and surfaces and should therefore inform policy decisions regarding community use. Some viral particles are stopped, particularly in the outward direction. Cloth masks can block droplet and aerosols and layers add efficiency. There is high-quality, consistent evidence that many, but not all, cloth masks reduce droplet and aerosol transmission and may be effective in reducing contamination of SARS-CoV-2. Consequences of community cloth mask use may include incorrect use of cloth masks or reduced hand hygiene because of a false sense of security, but these can be mitigated by controlling the distribution of equipment, clear messaging and public education. Last Updated: May 21, 2020
Non-medical masks and face coverings — Public Health Ontario	Organizational Scan	Last Updated: May 20, 2020
Non-medical masks and face coverings — Government of Canada	Organizational Scan	Last Updated: June 23, 2020
Washing Cloth Face Coverings — CDC: Centers for Disease Control and Prevention	Organizational Scan	Last Updated: May 21, 2020
Disclaimer: The summaries provided are distillations of reviews that have synthesized many individual studies. As such, summarized information may not always be applicable to every context. Each piece of evidence is hyperlinked to the original source.

1 Related Question

Are there formal exemptions to regulations requiring people to wear masks in workplace settings, such as for medical reasons? What happens if someone is unable to wear a mask when it is required at work? Or if a client of a service is unable or unwilling to wear a mask when participating in a program (i.e., groups or drop-in centres)?

The City of Toronto has imposed temporary regulations requiring employees of establishments that are open to the public, as well as the public, to wear masks within the establishment. This by-law does not apply to private and public transportation, schools, post-secondary institutions and childcare faculties, hospitals and independent healthcare facilities. However, these places and businesses can implement their own policy provided it follows occupational regulations. The City of Toronto has noted exemptions for mask use for those under the age of two years, persons with medical conditions, such as severe respiratory illness or certain allergies, who cannot wear masks safely, and those requiring assistance to place or remove masks. Those exempted should be allowed to enter the establishment, but it is recommended to minimize the number of times required to enter public buildings, avoid close contact with others, wash hands regularly and practise proper cough and sneeze etiquette. People should consider experimenting with different face coverings (i.e., cloth masks, face shields, bandanas, etc.) to find one that is comfortable and safe. Health Canada has outlined several options for homemade or purchased masks.

Employees who are exempt from wearing a mask should be accommodated by working in an area designated for them where there is no public access or where they can be behind a physical barrier for distancing such as plexiglass. Employers that require the use of masks for their employees may provide accommodations such as remote work, placement in non-public locations or roles, or, as a last resort, they may recommend different employment or work altogether if certain conditions for safety are challenging to meet. There is no regulation stating that employees or members of the public are required to provide proof of any exemption. It is recommended that if an employee cannot wear a mask due to medical reasons, they should contact their supervisor and/or their organization’s health and safety department for further instruction.