Back to home page Last updated: April 29, 2020
A wide array of references and resources (listed below) were obtained, reviewed, and analyzed during the development of the Everyone Gets a Mask! project kit. Many of the listings are annotated with informal summary comments made during our review. The conclusions we drew are incorporated into many of the documents, particularly the Basic Orientation and FAQs, Technical Specifications, Instructions for Mask Makers, one-page Handout for Mask Wearers, and detailed Instructions for Mask Wearers.
The data is very clear that all varieties of improvised and homemade face coverings are inferior to commercially manufactured and FDA-approved respiratory protection devices, whether surgical masks or N95 respirators. However, we found no evidence that homemade fabric face coverings are worse than wearing nothing at all, except for the ones that make breathing very difficult. In fact it appears that a high quality mask made of tightly woven 100% cotton material will filter out most (but not all) respiratory particles and up to half of the tiny particles (the size of aerosolized virus). In these early stages of the current pandemic, the choice has too often been between nothing and a homemade facial covering.
Moreover, we found significant differences in the effectiveness of homemade masks depending on (a) mask design and fit; (b) the materials with which they are constructed; and (c) the way they are handled during use. In fact, some very specific cotton fabrics filter respiratory particles almost as well as surgical masks (but not N95 respirators). Lastly, we found no evidence that wearing face masks reduces adherence to other preventive measures; in fact face masks can serve as a reminder to practice social distancing and to avoid touching the face.
These references were compiled in mid-March 2020 with the intent of updating them periodically as more information becomes available.
NOTE: Use your browser's search function to quickly locate items of interest.
Alessandro MM, Cichowicz JK Proper N95 Respirator Use for Respiratory Protection Preparedness. NIOSH Science Blog 2020;
bin-Reza F, Chavarrias VL, et al The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence. Influenza and Other Respiratory Viruses 2012; 6: 257-267
Updates his paper published in 2011. Examination of the literature has highlighted that well-designed studies in the field are challenging....None of the studies established a conclusive relationship between mask/ respirator use and protection against the influenza infection. Some evidence suggests that mask use is best undertaken as part of a package of personal protection, especially hand hygiene. The effectiveness of masks is likely linked to early and consistent usage.
Brosseau LD, Sietsema Commentary: Masks-for-all for COVID-19 not based on sound data. CIDRAP 2020;
The best evidence of mask and respirator performance starts with testing filter efficiency and then evaluating fit (facepiece leakage). Filter efficiency must be measured first. If the filter is inefficient, then fit will be a measure of filter efficiency only and not what is being leaked around the facepiece. For fibrous non-electret filters, this size is about 0.3 micrometers (µm); for electret filters, it ranges from 0.06 to 0.1 µm. When testing, we care most about the point of inefficiency. As flow increases, particles in this range will be collected less efficiently. For the entire range of particles tested, t-shirts had 10% efficiency, scarves 10% to 20%, cloth masks 10% to 30%, sweatshirts 20% to 40%, and towels 40%. All of the cloth masks and materials had near zero efficiency at 0.3 µm, a particle size that easily penetrates into the lungs.4 These studies demonstrate that cloth or homemade masks will have very low filter efficiency (2% to 38%). Medical masks are made fro a wide range of materials, and studies have found a wide range of filter efficiency (2% to 98%), with most exhibiting 30% to 50% efficiency.
CDC Interim guidance for Healthcare Personnel with Potential exposure to COVID-19. 2020;
CDC-NIOSH Recommended Guidance for Extended Use and Limited Reuse of N95 Filtering Facepiece Respirators in Healthcare Settings. 2020;
Centers For Disease Control Recommendation Regarding the Use of Cloth Face Coverings, Especially in Areas of Significant Community-Based Transmission. 4/3/2020;
We now know from recent studies that a significant portion of individuals with coronavirus lack symptoms (“asymptomatic”) and that even those who eventually develop symptoms (“pre-symptomatic”) can transmit the virus to others before showing symptoms. This means that the virus can spread between people interacting in close proximity—for example, speaking, coughing, or sneezing—even if those people are not exhibiting symptoms. In light of this new evidence, CDC recommends wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies) especially in areas of significant community-based transmission. It is critical to emphasize that maintaining 6-feet social distancing remains important to slowing the spread of the virus.
Davies, Thompson K Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic. Disaster Medicine and Public Health Preparedness 2013; 43: 1-6
A protective mask may reduce the likelihood of infection, but it will not eliminate the risk, particularly when a disease has more than 1 route of transmission. Thus any mask, no matter how efficient at filtration or how good the seal, will have minimal effect if it is not used in conjunction with other preventative measures, such as isolation of infected cases, immunization, good respiratory etiquette, and regular hand hygiene. An improvised face mask should be viewed as the last possible alternative if a supply of commercial face masks is not available, irrespective of the disease against which it may be required for protection. Improvised homemade face masks may be used to help protect those who could potentially, for example, be at occupational risk from close or frequent contact with symptomatic patients. However, these masks would provide the wearers little protection from microorganisms from others persons who are infected with respiratory diseases. As a result, we would not recommend the use of homemade face masks as a method of reducing transmission of infection from aerosols.
Elgin B, Tozzi J, Bass D Hospital Workers Make Masks From Office Supplies Amid U.S. Shortage. Bloomberg 2020;
On average, the homemade masks captured 7% fewer virus particles than the larger bacteria particles. However, all of the homemade materials managed to capture 50% of virus particles or more (with the exception of the scarf at 49%).
Greenhalgh T, et al What is the efficacy of standard face masks compared to respirator masks in preventing COVID-type respiratory illnesses in primary care staff?. CEBM 2020;
Standard surgical masks are as effective as respirator masks (e.g. N95, FFP2, FFP3) for preventing infection of healthcare workers in outbreaks of viral respiratory illnesses such as influenza. No head to head trial of these masks in COVID-19 has yet been published, and neither type of mask prevents all infection. Both types of mask need to be used in combination with other PPE measures. Respirator masks are recommended for protection during aerosol generating procedures (AGPs). Rapid reviews on wider PPE measures, and what counts as an AGP, are ongoing.
Hardin IR, Wilson SS, Dhandapani R, Dhende V An Assessment of the Validity of Claims for Bamboo Fibers. Aatcc Review 2009; 9
He S, Rosen L, Perry-Wolf Z Getting Protective Equipment (PPE) to Our Healthcare Heroes.
Herman AO, Sadoughi S, Sofair A SARS-CoV-2 May Be Transmissible Via "Normal Breathing"; Cloth Face Coverings Advised. NEJM Journal Watch 2020;
4/5/20: Viral RNA was detected in 40% of aerosols and 30% of respiratory droplets collected from participants without a face mask — but in none collected from those wearing a mask. The researchers with the latter study say the finding "has important implications for control of COVID-19." ...The CDC offers guidance on how to make and wear cloth masks on its website. Separately, a New York Times story examines the evidence on which materials might best filter out virus — think pillowcases and flannel pajamas, among others. Additionally, the Times quotes the following advice from Dr. Scott Segal, an anesthesiologist who's studied homemade masks: "Hold it up to a bright light. If light passes really easily through the fibers and you can almost see the fibers, it's not a good fabric. If it's a denser weave of thicker material and light doesn't pass through it as much, that's the material you want to use."
Hernandez LM, Xu EG, et al Plastic teabags release billions of microparticles and nanoparticles into tea. Environ. Sci. Technol 2019; 53: 12300-12310
Surfaces in ventilation grates also tested positive. None of the air samples was infectious in cell culture, but the data suggest that “viral aerosol particles are produced by individuals that have the COVID-19 disease, even in the absence of cough”, the authors write.
Huang S COVID-19: WHY WE SHOULD ALL WEAR MASKS — THERE IS NEW SCIENTIFIC RATIONALE. 2020;
3/26/20 - Great graphics Institute for Systems Biology
Jagadeesan K Chapter: Summary. Major Papers by Master of Science Students 2018;
University of Rhode Island-Textiles, Fashion Merchandising, and Design
Larson EL Preventing Transmission of Pandemic Influenza and Other Viral Respiratory Diseases: Personal Protective Equipment for Healthcare Personnel: Update 2010, Chapter 3. Designing and Engineering Effective PPE. National Academies Press (US 2011; 3
FINDINGS AND RECOMMENDATIONS 63
Lewis D Is the coronavirus airborne? Experts can’t agree. Nature 2020;
4/2/20: If SARS-CoV-2 is transmitting in aerosols, it is possible that virus particles can build up over time in enclosed spaces or be transmitted over greater distances.....A study of people with influenza found that 39% of people exhaled infectious aerosols5. As long as we are sharing an airspace with someone else, breathing in the air that they exhale, airborne transmission is possible, says Tang.
Lindsley W, Noti JD, Blachere FM, Szalajda JV, Beezhold DH Efficacy of Face Shields Against Cough Aerosol Droplets From a Cough Simulator. J Occup Environ Hyg 2014; 11: 509-518
For managing patient situations with low risk seasonal influenza, a medical mask is recommended. Medical masks for seasonal influenza in low risk situations, but were inconsistent for SARS in low risk situations, as well as pandemic influenza in low risk situations, and seasonal influenza in high risk situations.
Lindsley W, Pearce TA, Hudnall JB, et al. Quantity and Size Distribution of Cough-Generated Aerosol Particles Produced by Influenza Patients During and After Illness. J Occup Environ Hyg 2012; 9: 443-449
People with influenza release potentially infectious aerosol particles when they cough, sneeze, speak, and breathe. However, many questions remain about the likelihood of the transmission of influenza from person to person by the airborne route. Our study shows for the first time that individuals with influenza cough out a greater volume of aerosol particles than they do when they are healthy. Further, many of these particles are in the respirable size fraction.
Ma T, Shutler N How to Sew a Face Mask: A tutorial on how to make your own fabric face mask from common household materials. New York Times 2020;
Pattern Source, 3/31/20
MacIntyre CR, et al COVID-19, shortages of masks and the use of cloth masks as a last resort. BMJ Open- Infectios Disease Research 2020; 5
Published on: 30 March 2020: REsponse by author to his article: "We recommend that health workers should not work during the COVID-19 pandemic without respiratory protection as a matter of work health and safety. In addition, if health workers get infected, high rates of staff absenteeism from illness may also affect health system capacity to respond. Some health workers may still choose to work in inadequate PPE. In this case, the physical barrier provided by a cloth mask may afford some protection, but likely much less than a surgical mask or a respirator... However, none have been tested in a clinical trial for efficacy. If health workers choose to work using cloth masks, we suggest that they have at least two and cycle them, so that each one can be washed and dried after daily use. Sanitizer spray or UV disinfection boxes can be used to clean them during breaks in a single day. These are pragmatic, rather than evidence-based suggestions, given the situation. "
MacIntyre CR, Seals H, et al A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open- Infectios Disease Research 2015; 5
The study found that cloth mask wearers had higher rates of infection than even the standard practice control group of health workers, and the filtration provided by cloth masks was poor compared to surgical masks.
McCue TJ Calling All People Who Sew And Make: You Can Help Make Masks For 2020 Healthcare Worker PPE Shortage. Forbes 2020;
3/20/20 at 04:25am
Mechler S COVID-19 Disinfection and Sterilization of Face Masks for Viruses. The Chamber Blog, Consolidated Sterilizer Systems
VENDOR Publication: Unfortunately, many common [N-95] decontamination methods such as high temperature steam sterilization (6)(8), alcohol washing, bleach washing, and EtO (9) have been shown to degrade these types of respirator masks. On the bright side, disinfection through warm humid heat and UVGI was found to be effective at inactivating the H1N1 influenza virus and caused the least degradation of mask integrity. The use of hydrogen peroxide vapor (HPV) was found to maintain mask integrity while achieving sterilization....research is currently ongoing on methodologies to use existing autoclave infrastructure to achieve these conditions. [many good references cited]
National Academy of Sciences Reusability of Facemasks During an Influenza Pandemic: Facing the Flu (2006). National Academies Press (US) 2006;
The committee recognizes that in the absence of any alternative, some members of the public may improvise respiratory protection (e.g., T-shirts, handkerchiefs, or scarves) against transmission of influenza when it is necessary to enter an infected environment, such as when caring for an infected family member at home. Given the lack of sufficient data either supporting or refuting the effectiveness of such actions, the committee hesitates to discourage their use but cautions that they are not likely to be as protective as medical masks or respirators. The committee is concerned that their use might give wearers a false sense of protection that will encourage risk taking and/or decrease attention to other hygiene measures. The tighter the structure of the fabric, the better.
National Academy of Sciences, Engineering and Medicine Reusability of Facemasks During an Influenza Pandemic: Facing the Flu (2006)- Summary. National Academies Press (US) 2006;
Many factors will influence the effectiveness of respiratory protection used by both healthcare workers and the public to mitigate thepotential infection in the event of an influenza pandemic. Experience with previous efforts to improve infection control in the hospital and elsewhere have demonstrated that the efficacy of an intervention alone does not guarantee its success. The best respirator or medical mask will do little to protect the individual who refuses, or who misunderstands how and when, to use it correctly. Any public health effort aimed at extending the usefulness of existing devices must be delivered with clarity and truthfulness. The public is likely to forgive lack of knowledge but will not be willing to trust public health officials in the next instance if they have in any way been misinformed or misled.
National Association for Home Care & Hospice COVID-19 Frequently Asked Questions. Hospice & Homecare
Laundering in hot water, preferably with chlorine, and drying on a 50 minute dry cycle at high heat is sufficient.
Patil LG, Bhute A, Bhokare P Nonwoven for filtration. Textiles Today - Technical Textiles 2014;
Price A, Chu L Addressing COVID-19 Face Mask Shortages [v1.2] . 2020;
Good graphics and discussion.
Price A, Chu L Addressing COVID-19 Face Mask Shortages [v1.3]: Can face masks be safely disinfected and reused?. Stanford Medicine 2020;
Rang C Face masks for covid-19 relief. Instructables Craft
Woman interviewed in Forbes. Excellent list of references.
Ratala WA, Weber DJ, Healthcare Infection Control Practices Advisory Committee Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008; Update : May 2019. 2019;
Reck S Olson Mask - UnityPoint Health, edited by Avera.
ter the potential for filtration. At the same time, as the tightness of the structure increases, breathing resistance increases, thereby affecting the user’s comfort while using the device. This may affect usage. The level of protection offered also may be contingent on the tightness of the fit of the device to the wearer’s face.
Rengasamy S, Eimer B, Shaffer RE Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm Size Particle. The Annals of Occupational Hygiene 2010; 54: 789-798
https://academic.oup.com/annweh/article/54/7/789/202744 or https://doi.org/10.1093/annhyg/meq044
Common fabric materials of five major categories including sweatshirts, T-shirts, towels, scarves, and cloth masks were selected for aerosol penetration tests (Table 1). Table 1 also shows the fiber composition of fabric materials and the resistance levels measured at 5.5 cm s−1 face velocity. The fiber composition for cloth masks is not available. Fabric materials for each category were randomly selected from three different manufacturers based on availability. The penetration levels for these fabric materials against polydisperse, as well as monodisperse aerosols, were much higher than the values for the control N95 respirator filter media. A poor filtration performance is expected for improvised fabric materials because these materials are not designed for respiratory protection. ... Thus, the penetration results obtained in the study indicate that the filtration performance of fabric materials is similar in some aspects to some surgical masks to reduce the transmission of infectious diseases. However, this study did not evaluate the fabric materials for protection against droplets and liquid splashes... The penetration values obtained for common fabric materials indicate that only marginal respiratory protection can be expected for submicron particles taking into consideration face seal leakage.
Robertson P What Are The Best Materials for Making DIY Masks?. Vendor publication - Smart filters 2020;
Vendor site - great graphics, used in our papers.
Robertson P Can DIY Masks Protect Us from Coronavirus?. Vendor publication - Smart filters 2020;
Santarpia JL , et al. Evolving Epidemiology and Impact of Non-pharmaceutical Interventions on the Outbreak of Coronavirus Disease 2019 in Wuhan, China. School of Public Health, Tongji Medical College, Huazhong University of Science and Technology 2020;
Despite that the outbreak started in early December, no strong interventions were taken before January 20 when the human-to-human transmission was officially announced. February 1, the local government first blocked all outbound transportations on January 23 and subsequently suspended public transit and banned all vehicular traffic within the city. Other social distancing measures were also implemented, including compulsory mask-wearing in public places and cancellation of social gathering. ...e data from January 1, 2020, when the Huanan Seafood Market was closed. We assumed a constant population size of 10 million of Wuhan with equal daily inbound and outbound travelers (500,000 for January 1-10, 800,000 for January 11-22 due to Chunyun, and 0 afterwards due to cordon sanitaire since January 23). ...Healthcare workers and elderly people had higher attack rates and severity risk increased with age.........The interventions were estimated to prevent 94.5% (93.7 to 95.2%) infections till February 18….Considerable countermeasures have effectively controlled the Covid-19 outbreak in Wuhan. ...Special efforts are needed to protect vulnerable populations, including healthcare workers, elderly and children.
Segal S FP95’s - A DIY Surgical Mask.
Wake Forest Institute of Regenerative Medicine, 4/3/20. NBC News. "The best masks were constructed of 2 layers of heavyweight "Quilters cotton" with a thread count of at least 180 and a thicker tighter weave." Lesser quality fabrics worked well if had an internal layer of flannel. Don't want to use knit, fabric because the holes between the knit stitches are bigger. Avoid bleach or harsh chemicals - don't know effects on fabrics. Use ties around ears, can be adjusted better than elastics. Make sure to use dry masks- wet more likely to transmit virus. Wash with detergent in regular washing machine.
Smith K, Ford C COVID-19.
Stewart A A Seattle-area hospital system is asking volunteers to sew fabric masks to make up for a shortage of protective gear to fight COVID-19. Business Insider 2020;
Subhash SS, Cavaiuolo M, Radonovich Jr LJ, Eagan A, Lee ML, Campbell S, Martinello RA Effectiveness of Common Healthcare Disinfectants against H1N1 Influenza Virus on Reusable Elastomeric Respirators. Infection Control and Hospital Epidemiology 2014; 35: 894-897
The National Personal Protective Technology Laboratory (NPPTL), NIOSH Respirator Trusted-Source Information. CDC- NIOSH 2018;
van der Sande M, Teunis P , Sabel R Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. PLoS One 2008; 3: e2618
All types of masks reduced aerosol exposure, relatively stable over time, unaffected by duration of wear or type of activity, but with a high degree of individual variation. Personal respirators were more efficient than surgical masks, which were more efficient than home-made masks. Regardless of mask type, children were less well protected. Outward protection (mask wearing by a mechanical head) was less effective than inward protection (mask wearing by healthy volunteers). Any type of general mask use is likely to decrease viral exposure and infection risk on a population level, in spite of imperfect fit and imperfect adherence, personal respirators providing most protection. Masks worn by patients may not offer as great a degree of protection against aerosol transmission....although this could imply that individual subjects may not always be optimally protected, from a public health point of view, any type of general face mask usage can still decrease viral transmission. Also, it is important not to focus on a single intervention in case of a pandemic, but to integrate all effective interventions for optimal protection....he difference in measured protection against inward and outward protection is remarkable, and cannot be explained from the available data as we only measured the overall effect. A differential effect on the amount of leakage seems most plausible. At the same time, we cannot exclude that wearing of face masks, even FFP2 or surgical masks by patients might still significantly reduce transmission. However, the observed limited particle retention in our experiments may still be an overestimate of protection, as it may for instance be challenging to enforce adherence to mask wearing by a patient who is short of breath. Wearing of masks by caregivers might be more feasible and more effective, in particular where additional preventive measures are in place as well for caregivers....And although our simulated patient varied its breathing frequency, we have not assessed the impact of e.g. coughing or sneezing on outward transmission through a mask.
van der Sande M, Teunis P, Sabel R Professional and home-made face masks reduce exposure to respiratory infections among the general population. PLoS One 2008; 3: e2618
Conclusions/Significance: Any type of general mask use is likely to decrease viral exposure and infection risk on a population level, in spite of imperfect fit and imperfect adherence, personal respirators providing most protection. Masks worn by patients may not offer as great a degree of protection against aerosol transmission.
Vanderbilt Hospital Coronavirus (COVID-19) Information for Employees and Patients - How to Donate Hand-Sewn Face Masks. 2020;
Virginia Cooperative Extension Service Virginia Tech and Virginia State Sewing Silk and Silk-Like Fabrics. Virginia's Land-grant Universities ,Publication 1985; 346: 43834
Wilkerson L, Wathen CA How to Make a Face Mask and Donate. 2020;
Donation Site. Deaconess Hospital.
Wilkerson L, Wathen CA How to Make a Face Mask. 2020;
Pattern Source, rectangular with elastic ear pieces.
Williams LM BENDING PROPERTIES OF A LIGHTWEIGHT SUITING FABRIC AS AFFECTED BY A FUSIBLE AND A NONFUSIBLE INTERFACING. 1987;
Virginia Polytechnic Institute and State University.
Wölfe R, et al Virological assessment of hospitalized patients with COVID-2019. Nature 2020;
https://www.nature.com/articles/s41586-020-2196-x_reference.pdf or https://doi.org/10.1038/s41586-020- 2196-x (2020).
Published 4/1/20. This is a PDF file of a peer-reviewed paper that has been accepted for publication. Critically, the majority of patients in the present study seemed to be already beyond their shedding peak in upper respiratory tract samples when first tested, while shedding of infectious virus in sputum continued through the first week of symptoms. ...Our initial results suggest that measures to contain viral spread should aim at droplet-, rather than fomite-based transmission. The prolonged viral shedding in sputum is relevant not only for hospital infection control, but also for discharge management.... When aligned to viral load courses, it seems there is no abrupt virus elimination at the time of seroconversion. Rather, seroconversion early in week 2 coincides with a slow but steady decline of sputum viral load.
Yang S, Lee GWM, Chen CM, et al The Size and Concentration of Droplets Generated by Coughing in Human Subjects. Journalof Aerosol Medicine 2007; 20
Results indicated the total average size distribution of the droplet nuclei was 0.58–5.42 μm, and 82% of droplet nuclei centered in 0.74–2.12 μm. The entire average size distribution of the coughed droplets was 0.62–15.9 μm, and the average mode size was 8.35 μm. The size distribution of the coughed droplets was multimodal. size distribution of coughed droplets showed three peaks at approximately 1 μm, 2 μm, and 8 μm. These analytical findings indicate that variation for average droplet size among the three age groups was insignificant (p > 0.1). Moreover, the variation in average droplet size between males and females was also insignificant (p > 0.1). Also, the variation in droplet concentration between males and females was significant (p > 0.1).Droplet nuclei concentrations from male subjects were considerably higher than that from females. Comparison of the droplet concentrations for subjects in different age groups demonstrated that subjects in the 30–50-year age group have the largest droplet concentrations.
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Jennifer Christian MD
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Claudia G. Hix DO
Occupational Health Works, LLC
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