Do homemade face masks work as a preventive measure for respiratory virus ntransmission?
Date First Published:
April 13, 2020
Last Updated:
April 13, 2020
Report by:
Florentine Leirman, Nicky Koster, medical students (KU Leuven)
Search checked by:
Dr. Nicolas Delvaux, Mrs. Gerlinde Lenaerts, Prof Dr Bert Aertgeerts, Prof Dr Jan Verbakel, KU Leuven
Three-Part Question:
Do [homemade face masks] work as a preventive measure in [the general population] for [respiratory virus transmission]?
Clinical Scenario:
Since the outbreak of COVID-19, we are facing an imminent shortage of surgical facemasks and respirators to protect patients and healthcare workers. Inspired by the widespread use of cloth masks in Asia, alternatives out of cotton and old bras are on the rise in Belgium. This raises the question whether these homemade facemasks are effective in the prevention of virus
transmission. And if so, which materials are most suitable.
transmission. And if so, which materials are most suitable.
Search Strategy:
Pubmed, Embase, Cochrane and the specific COVID-19 database LitCovid, conception until 20/03/2020
Search Details:
"Masks"[Mesh], “Viruses"[Mesh], "Coronavirus"[Mesh], infection, "Respiratory Protective Devices"[Mesh], "Developing Countries"[Mesh], "Masks"[Mesh], "Influenza, Human"[Mesh], 'surgical mask'/exp, 'mask'/exp, 'coronavirinae'/exp, 'droplet infection'/exp, 'cloth mask', virus, 'cotton'/exp, 'respiratory tract infection'/exp, 'cotton'/exp, 'face mask'/exp, 'coronavirinae'/exp, 'face mask'/exp, 'influenza virus'/exp,
Mask, droplet infection, coronavirinae, “homemade protection masks “, "Pandemics"[Mesh], "Masks/statistics and numerical data"[Mesh], "Respiratory Protective Devices"[Mesh], "Cotton Fiber"[Mesh], cotton,
nanofabric, microfiber, muslin, influenza, respiratory infection, “cloth masks”
Mask, droplet infection, coronavirinae, “homemade protection masks “, "Pandemics"[Mesh], "Masks/statistics and numerical data"[Mesh], "Respiratory Protective Devices"[Mesh], "Cotton Fiber"[Mesh], cotton,
nanofabric, microfiber, muslin, influenza, respiratory infection, “cloth masks”
Outcome:
848 articles
Relevant Paper(s):
| Study Title | Patient Group | Study type (level of evidence) | Outcomes | Key results | Study Weaknesses |
|---|---|---|---|---|---|
| A cluster randomised trial of cloth masks compared with medical masks in healthcare workers MacIntyre CR 2015 | -t1607 healthcare workers (HCW) > 18 y/o (nurses and doctors) -t14 secundary/ tertiairy -tHospitals in Hanoi |
Randomised controlled trial -tCluster randomisation by using Epi info V.6 for allocation of 74 wards (emergency, infectious/respiratory disease, intensive care and paediatrics) containing 1607 HCW. -tDaily follow-up -tLabo testing and results were blinded. Clinical end points unblinded. -tCompliance monitored by a self- reporting mechanism. -tITT analysis, yet no withdrawals. |
Rates of all infection outcomes highest in the cloth mask arm | ILI (relative risk (RR) =13.00, 95% CI 1.69 to 100.07) | -tNo allocation bias -tNo withdrawal bias -tNo attrition bias -tNo reporting bias -tAscertainment bias due to unblinded clinical end points, since a facemask is a visible intervention. -tLack of a no-mask control group: high rate of mask use in the controls through standard practice mask use impedes interpretation. -tRecall bias: compliance was measured through a self-reporting mechanism. -tQuality of cloth masks varies, not generalizable. |
| ILI and confirmed viral infections | ILI (RR = 6.64; 95% CI 1.45 to 28.65) and confirmed viral infections (RR = 1.72; 95% CI 1.01 to 2.94) significantly higher in cloth mask group | ||||
| Penetration | cloth masks 97%, medical masks 44% | ||||
| Facemasks for the prevention of infection in healthcare and community settings MacIntyre CR 2015 Vietnam | People in community setting and healthcare setting | Review (not SR) of 9 cluster RCT’s, of which 3 concerning cloth facemasks: - Larson et al. 2009 (open label) (3) - Cowling et al. 2010 (single blind) (4) - Suess et al. 2012 (single blind) (5) |
Community setting | people in high risk settings could benefit from facemasks. | -tConfounding effect due to pooled analysis with medical masks or simultaneous use of hand sanitizer. -tLow compliance -tSelf-reporting bias -tPerformance bias: use of masks in control group. -tSuboptimal fit of the masks |
| Healthcare setting | only medical masks and respirators offer enough protection. | ||||
| use of cloth masks | cloth masks only when no other option | ||||
| Compliance | Compliance is a determinant of protection. | ||||
| Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? Disaster Medicine and Public Health Preparedness Davies 2013 | -tHealthy volunteers -t12 men, 9 women ( 20-44 y/o) |
In-vitro and in-vivo observational study | filter efficiency | Household materials have a filter efficiency of 50-89% against 20nm particles | -tNot enough power -tHigher than realistic compliance -tSuboptimal fit of the mask -tPopulation sampling error possible |
| forming of bacterial colonies | No difference in forming of bacterial colonies | ||||
| Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. Van der Sande 2008 | -t1st exp: 28 adults and 11 children (5- 11y/o) -t2nd exp: 22 adults (10 men en 12 women) -t3rd exp: artificial in- vitro |
In-vitro and in-vivo observational study | protection | Protection mainly depends on type of mask. | -tNot enough power -tHigher than realistic compliance -tNo data on couching -tPopulation sampling error possible |
| degree of protection | Tea cloth masks still offer some degree of protection | ||||
| decay of protection | Protection decreases over time | ||||
| Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm Size Particles Rengasamy 2010 USA | not applicable | In-vitro observational study | penetration | Cloth 74-90%. -tCotton/polyester T- shirt 40-% depending on composition. -tCotton T-shirt > 85%. - Towel 60-66%. - Scarf 73-89%. | -tNot enough power -tUse of nano- particles, not viruses -tSampling error of fabrics possible |
| Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure Shakya 2017 USA | not applicable | In-vitro observational study | penetration of regular cloth masks | 60-80% by particles < 100nm | -tNot enough power -tUse of nano- particles, not viruses -tSampling error of fabrics possible |
| Experimental evaluation of personal protection devices against graphite nanoaerosols: fibrous filter media, masks, protective clothing, and gloves. Golanski 2009 France | not applicable | In-vitro observational study | penetrance | Cotton has a penetrance of 27% at low velocity particle flow. Industrial fabrics are significantly less penetrable. | -tNot enough power -tUse of nano- particles, not viruses -tSampling error of fabrics possible -tVelocity of particle flow is not representative for airflow when breathing or coughing. |
Author Commentary:
None of the in-vivo studies recommend the use of cloth facemasks as they offered poor protection against viruses. In-vitro studies showed that household materials such as cotton and cotton-polyester blend are mostly permeable for virus-sized particles.
The level of protection provided by homemade facemasks is mainly determined by the used material, compliance and correctness of fit.
The majority of studies caution against the use of cloth masks made of fabrics such as cotton or cotton-polyester blend, for the prevention of virus transmission, especially for health care professionals. Infection rates have shown to be much higher in cloth masks compared to disposable medical masks. Hence, most of these masks are over 50% permeable to nanometer-range particles, and therefore provide very little protection to the COVID-19 droplet particles which range from 50 to 200 nm.
Heavy materials such as towels and tea cloths perform slightly better compared to T-shirts, yet have to compromise on respiratory comfort, which reduces the compliancy of use. Furthermore, due to a poor fit, leakage of viral particles reduces their protective effect.
However, if respirators or surgical masks are not available in a pandemic, cloth masks may be used on the principle that ‘something is better than nothing’. Nevertheless, this strategy is highly discouraged for healthcare workers, who are at a higher risk of exposure, given that a cloth mask will not provide sufficient protection.
Scientific data are sparse. Other than one RCT, no studies have been conducted concerning the efficacy of cloth masks, due to the introduction of disposable medical masks and respirators. Consequently, it is difficult to determine whether these homemade cloth masks offer any clinical protection. Further profound research and international guidelines are needed.
The level of protection provided by homemade facemasks is mainly determined by the used material, compliance and correctness of fit.
The majority of studies caution against the use of cloth masks made of fabrics such as cotton or cotton-polyester blend, for the prevention of virus transmission, especially for health care professionals. Infection rates have shown to be much higher in cloth masks compared to disposable medical masks. Hence, most of these masks are over 50% permeable to nanometer-range particles, and therefore provide very little protection to the COVID-19 droplet particles which range from 50 to 200 nm.
Heavy materials such as towels and tea cloths perform slightly better compared to T-shirts, yet have to compromise on respiratory comfort, which reduces the compliancy of use. Furthermore, due to a poor fit, leakage of viral particles reduces their protective effect.
However, if respirators or surgical masks are not available in a pandemic, cloth masks may be used on the principle that ‘something is better than nothing’. Nevertheless, this strategy is highly discouraged for healthcare workers, who are at a higher risk of exposure, given that a cloth mask will not provide sufficient protection.
Scientific data are sparse. Other than one RCT, no studies have been conducted concerning the efficacy of cloth masks, due to the introduction of disposable medical masks and respirators. Consequently, it is difficult to determine whether these homemade cloth masks offer any clinical protection. Further profound research and international guidelines are needed.
Bottom Line:
Homemade face masks provide insufficient protection against viruses. Therefore, their use is cautioned in any health care setting.
References:
- MacIntyre CR. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers
- MacIntyre CR. Facemasks for the prevention of infection in healthcare and community settings
- Davies. Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? Disaster Medicine and Public Health Preparedness
- Van der Sande . Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population.
- Rengasamy. Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm Size Particles
- Shakya. Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure
- Golanski. Experimental evaluation of personal protection devices against graphite nanoaerosols: fibrous filter media, masks, protective clothing, and gloves.