Science Brief: Community Use of Masks to Control the Spread of SARS-CoV-2
COVID-19 Science Briefs provide a summary of the scientific evidence used to inform specific CDC guidance and recommendations. The Science Briefs reflect the scientific evidence, and CDC’s understanding of it, on a specific topic at the time of the Brief’s publication. Though CDC seeks to update Science Briefs when and as appropriate, given ongoing changes in scientific evidence an individual Science Brief might not reflect CDC’s current understanding of that topic. As scientific evidence and available information on COVID-19 change, Science Briefs will be systematically archived as historic reference materials.
Page First Published Nov 10, 2020 | View Page Updates
SARS-CoV-2 infection is transmitted predominantly by inhalation of respiratory droplets generated when people cough, sneeze, sing, talk, or breathe. CDC recommends community use of masks to prevent transmission of SARS-CoV-2. Masks are primarily intended to reduce the emission of virus-laden droplets by the wearer (“source control”), which is especially relevant for asymptomatic or presymptomatic infected wearers who feel well and may be unaware of their infectiousness to others (estimated to account for more than 50% of SARS-CoV-2 transmissions).1, 2 Masks also help reduce inhalation of these droplets by the wearer (“filtration for wearer protection”). The community benefit of masking for SARS-CoV-2 control is due to the combination of these two effects (source control and filtration for wearer protection); individual prevention benefit increases with increasing numbers of people using masks consistently and correctly.
Source Control to Block Exhaled Virus
Multi-layer cloth masks block release of exhaled respiratory particles into the environment,3-6 along with any microorganisms associated with these particles.7, 8 Cloth masks not only effectively block most large droplets (i.e., 20-30 microns and larger),9 but they can also block the exhalation of fine droplets and particles (also often referred to as aerosols) smaller than 10 microns3, 5 which increase in number with the volume of speech10-12 and specific types of phonation.13 Multi-layer cloth masks can both block 50-70% of these fine droplets and particles3, 14 and limit the forward spread of those that are not captured.5, 6, 15, 16 Upwards of 80% blockage has been achieved in human experiments,4 with cloth masks in some studies performing on par with surgical masks as barriers for source control.3, 9, 14, 17 In one study, conducted prior to widespread circulation of the Delta variant, masks worked equally well for blocking aerosolized particles containing both “wild-type” virus and the Alpha variant (a more infectious variant).17
Filtration for Wearer Protection
Studies demonstrate that cloth mask materials can also reduce wearers’ exposure to infectious droplets through filtration, including filtration of fine droplets and particles less than 10 microns. The relative filtration effectiveness of various masks has varied widely across studies, in large part due to variation in experimental design and particle sizes analyzed. Multiple layers of cloth with higher thread counts have demonstrated superior performance compared to single layers of cloth with lower thread counts, in some cases filtering nearly 50% of fine particles less than 1 micron.14, 18-30 Some materials (e.g., polypropylene) may enhance filtering effectiveness by generating triboelectric charge (a form of static electricity) that enhances capture of charged particles20 while others (e.g., silk) may help repel moist droplets31 and reduce fabric wetting and thus maintain breathability and comfort. In addition to the number of layers and choice of materials, other techniques can improve wearer protection by improving fit and thereby filtration capacity. Examples include but are not limited to mask fitters, knotting-and-tucking the ear loops of medical procedures masks, using a cloth mask placed over a medical procedure mask, and nylon hosiery sleeves.32-36
Human Studies of Masking and SARS-CoV-2 Transmission
- A large, well-designed cluster-randomized trial in Bangladesh in late 2020 found that surgical or cloth mask distribution, role-modeling, and active mask promotion tripled mask use to 42.3% in intervention villages compared to 13.3% in comparison villages. In villages receiving mask interventions, symptomatic seroprevalence of SARS-CoV-2 was reduced by approximately 9% relative to comparison villages. In villages randomized to receive surgical masks, symptomatic seroprevalence of SARS-CoV-2 was significantly lower (relative reduction 11.1% overall). The results of this study show that even modest increases in community use of masks can effectively reduce symptomatic SARS-CoV-2 infections (COVID-19).37
- A study of an outbreak aboard the USS Theodore Roosevelt, an environment notable for congregate living quarters and close working environments, found that use of face coverings on-board was associated with a 70% reduced risk of infection.38
- In a study of 124 Beijing households with > 1 laboratory-confirmed case of SARS-CoV-2 infection, mask use by the index patient and family contacts before the index patient developed symptoms reduced secondary transmission within the households by 79%.39
- A study examining SARS-CoV-2 secondary attack rates among eight public K-12 school districts in Massachusetts (70 schools with >33,000 enrolled students) during the 2020–21 school year found an unadjusted secondary attack rate of 11.7% for unmasked versus 1.7% for masked interactions.40
- A retrospective case-control study from Thailand documented that, among more than 1,000 persons interviewed as part of contact tracing investigations, those who reported having always worn a mask during high-risk exposures experienced a greater than 70% reduced risk of acquiring infection compared with persons who did not wear masks under these circumstances.41
- During July 15–August 31, 2021, when Delta was the predominant strain circulating in the U.S., about one in five K–12 public non-charter schools open for in-person learning in Maricopa and Pima Counties, Arizona, experienced a school-associated outbreak. Outbreaks were three and a half times more likely (adjusted odds ratio 3.5, 95% confidence interval 1.8-6.6) in schools without mask mandates.42
- In a nationwide analysis of data collected during July 1-September 4, 2021, U.S. counties without school mask requirements experienced larger increases in pediatric COVID-19 case rates (18.53 per 100,000 per day more cases) after the start of school compared with counties with school mask requirements.43
- An investigation of a high-exposure event in the U.S., in which 2 symptomatically ill hair stylists interacted for an average of 15 minutes with each of 139 clients during an 8-day period, found that none of the 67 clients who subsequently consented to an interview and testing developed infection. The stylists and all clients universally wore masks in the salon as required by local ordinance and company policy at the time.44
- Investigations involving infected passengers aboard flights longer than 10 hours strongly suggest that masking prevented in-flight transmissions, as demonstrated by the absence of infection developing in other passengers and crew in the 14 days following exposure.45, 46
At least ten studies have confirmed the benefit of universal masking in community level analyses: in a unified hospital system,47 a German city,48 two U.S. states,49, 50 a panel of 15 U.S. states and Washington, D.C.,51, 52 as well as both Canada53 and the U.S.54-56 nationally. Each analysis demonstrated that, following directives from organizational and political leadership for universal masking, new infections fell significantly. Two of these studies51, 52 and an additional analysis of data from 200 countries that included the U.S.56 also demonstrated reductions in mortality. Another 10-site study showed reductions in hospitalization growth rates following mask mandate implementation.54 A separate series of cross-sectional surveys in the U.S. suggested that a 10% increase in self-reported mask wearing tripled the likelihood of stopping community transmission.57 An economic analysis using U.S. data found that, given these effects, increasing universal masking by 15% could prevent the need for lockdowns and reduce associated losses of up to $1 trillion or about 5% of gross domestic product.52
Two studies have been improperly characterized by some sources as showing that surgical or cloth masks offer no benefit.58,59 A community-based randomized control trial in Denmark during 2020 assessed whether the use of surgical masks reduced the SARS-CoV-2 infection rate among wearers (personal protection) by more than 50%.58 Findings were inconclusive,58 most likely because the actual reduction in infections was lower. The study was too small (i.e., enrolled about 0.1% of the population) to assess whether masks could decrease transmission from wearers to others (source control). A second study of 14 hospitals in Vietnam during 2015 found that cloth masks were inferior to surgical masks for protection against clinical upper respiratory illness or laboratory-confirmed viral infection.59 The study had a number of limitations including the lack of a true control (no mask) group for comparison, limited source control as hospitalized patients and staff were not masked, unblinded study arm assignments potentially biasing self-reporting of illness, and the washing and re-use of cloth masks by users introducing the risk of infection from self-washing. A follow up study in 2020 found that healthcare workers whose cloth masks were laundered by the hospital were protected equally as well as those that wore medical masks.60
Potential Adverse Health Effects of Mask Wearing
Research supports that under most circumstances, mask wearing has no significant adverse health effects for wearers. Studies of healthy hospital workers, older adults, and adults with chronic obstructive pulmonary disease (COPD) reported no to minimal changes in oxygen or carbon dioxide levels while wearing a cloth or surgical mask either during rest or moderate physical activity.61-65 The safety of mask use during low to moderate levels of exercise has been confirmed in studies of healthy adults and adolescents.64, 66-70 Some,71-74 but not all,67 studies have found that during intense exercise, especially when approaching the aerobic threshold, wearing a mask can increase dyspnea (difficulty breathing), perceived exertion, and claustrophobia, and produce modest negative effects on measured cardiopulmonary parameters. In some people, face masks worn for longer durations might be associated with skin reactions such as acne, itching, dry skin and worsening of existing dermatoses.75-77 Wearing a surgical mask and N95 respirator may have a higher risk of skin reactions compared with a cloth mask.76-78
A study of 60 elementary school children reported no adverse cardiovascular (e.g., heart rate) or pulmonary (e.g., peripheral oxygen saturation) effects among children while wearing a cloth face covering in a classroom for 30 consecutive minutes of instructional time.79 A separate study observed no oxygen desaturation or respiratory distress after 60 minutes of monitoring among children less than 2 years of age when masked during normal play.80 A randomized trial among 40 children aged 3–10 years old scheduled for elective surgery, found that protective surgical face masks could be used safely in the postoperative period.81 In a prospective school-based cohort study of children aged 10–17 years who wore masks for 6–7 hours during the school day, some children self-reported general (4–7%) or situation-specific (2–4%) side-effects such as skin irritation, headache, or difficulty breathing during physical education.82
The potential impact of masks on language and emotional development has been examined in several studies.83-89 Some research suggests children and adults, and especially toddlers (aged 3–5 years) can have difficulty inferring emotion from facial features presented on photographs of persons with their lower facial features covered by a mask.83 However, a study of 7- to 13-year-old children determined the decrement in emotional inference observed when the lower half of a photographed face was covered with a mask was equivalent to that associated with covering the eyes with sunglasses, leading the authors to conclude that in combination with other contextual cues, masks are unlikely to produce serious impairments of children’s social interactions.84 A study of 2-year-old children concluded that they were able to recognize familiar words presented without a mask and when hearing words through opaque masks.85 Among children with autism spectrum disorders (ASD), interventions including positive reinforcement and coaching caregivers to teach mask wearing have improved participants’ ability to wear a face mask.86-88 These findings suggest that even children who may have difficulty wearing a mask can do so effectively through targeted interventions.
Experimental and epidemiologic data support community masking to reduce the spread of SARS-CoV-2, including alpha and delta variants, among adults and children. The prevention benefit of masking is derived from the combination of source control and wearer protection. The relationship between source control and wearer protection is likely complementary and possibly synergistic, so that individual benefit increases with increasing community mask use. Mask use has been found to be safe and is not associated with clinically significant impacts on respiration or gas exchange under most circumstances, except for intense exercise. The limited available data indicate no clear evidence that masking impairs emotional or language development in children. Further research is needed to assess masks, particularly to identify the combinations of materials that maximize both their blocking and filtering effectiveness, as well as fit, comfort, durability, and consumer appeal.
|Type of investigation||Location||Study months||Population studied||Intervention||Outcome|
|Abaluck37||Cluster-randomized trial||Bangladesh||Nov 2020–April 2021||342,183 adults in 572 villages||Mask promotion strategies||In villages receiving mask interventions, symptomatic seroprevalence of SARS-CoV-2 was reduced by approximately 9% (adjusted prevalence ratio 0.91, 95% CI 0.82-1.00) relative to comparison villages|
|Payne38||Cohort study||USS Theodore Roosevelt, Guam (USA)||March 2020||382 U.S. Navy service members||Mask wearing (self-report)||Masking reduced risk of infection by 70% (unadjusted OR 0.30, 95% CI = 0.17–0.52)|
|Wang Y39||Cohort study||Households in Beijing (China)||February–March 2020||124 households of diagnosed cases comprising 335 people||Mask wearing by index cases or >1 household member prior to index case’s diagnosis (self-report)||Masking reduced risk of secondary infection by 79% (adjusted OR 0.21, 95% CI = 0.06–0.79)|
|Hendrix44||Cohort study||Hair salon in Springfield, MO (USA)||May 2020||2 symptomatically infected stylists and 139 patrons||Universal masking in salon (by local ordinance and company policy)||No COVID-19 infections among 67 patrons who were tested in follow-up|
|Doung-Ngern41||Case-control study||Bangkok (Thailand)||April–May 2020||839 close contacts of 211 index cases||Mask wearing by contact at time of high-risk exposure to case (self-report)||Always having used a mask reduced infection by 77% (adjusted OR 0.23, 95% CI = 0.096–0.60)|
|Gallaway49||Population-based intervention||Arizona (USA)||January–August 2020||State population||Mandatory mask wearing in public||Temporal association between institution of masking policy and subsequent decline in new diagnoses|
|Rader57||Serial cross-sectional surveys||USA||June–July 2020||374,021 persons who completed web-based surveys||Self-reported mask wearing in grocery stores and in the homes of family or friends||10% increase in mask wearing tripled the likelihood of stopping community transmission (adjusted OR 3.53, 95% CI = 2.03-6.43)|
|Wang X47||Population-based intervention with trend analysis||Boston, MA (USA)||March– April 2020||9,850 healthcare workers (HCW)||Universal masking of HCW and patients, Mass General Brigham health care system||Estimated daily decline in new diagnoses among HCW of 0.49%|
|Mitze48||Population-based intervention with trend analysis||Jena (Thuringia), Germany||April 2020||City population aged >15 years||Mandatory mask wearing in public spaces (e.g., public transport, shops)||Estimated daily decline in new diagnoses of 1.28 percentage points|
|Van Dyke50||Population-based intervention with trend analysis||Kansas (USA)||June– August 2020||State population||Mandatory mask wearing in public spaces||Estimated case rate per 100,000 decreased by 0.08 in counties with mask mandates but increased by 0.11 in those without|
|Lyu and Wehby51||Population-based intervention with trend analysis||15 U.S. states and Washington, DC||March– May 2020||State population||Mandatory mask wearing in public||Estimated overall initial daily decline in new diagnoses of 0.9%, grew to 2.0% at 21 days following mandates|
|Joo54||Population-based intervention with trend analysis||USA||March–October 2020||State populations||Mandatory mask wearing in public||Estimated decline in weekly hospitalization rates by 5.6 percentage points for adults aged 18–64 years after mandate implementation, compared with growth rates during the 4 weeks preceding implementation of the mandate|
|Guy56||Population-based intervention with trend analysis||2,313 counties, USA||March–December 2020||County population||Mandatory mask wearing in public||Estimated overall initial daily decline in new diagnoses of 0.5%, grew to 1.8% at 81–100 days following mandates; estimated overall initial daily decline in deaths of 0.7%, grew to 1.9% at 81-100 days following mask mandate implementation|
|Jehn42||Population-based intervention with trend analysis||Arizona (USA)||July–August 2021||1,020 K–12 schools||School mask policies||Odds of a school-associated COVID-19 outbreak in schools without a mask requirement were 3.5 times higher than those in schools with an early mask requirement (OR = 3.5; 95% CI = 1.8–6.9)|
|Budzyn43||Population-based intervention with trend analysis||USA||July–September 2021||520 counties||School mask requirements||Increases in pediatric COVID-19 case rates during the start of the 2021–22 school year were smaller in U.S. counties with school mask requirements than in those without school mask requirements|
|Karaivanov53||Counterfactual modeling using national data||Canada||March–August 2020||County population||Mandatory mask wearing indoors||Estimated weekly 22% decline in new diagnoses following mask mandates|
|Chernozhukov55||Counterfactual modeling using national data||USA||March–May 2020||State population||Mandatory mask wearing for employees in public businesses||Nationally mandating face masks for employees early in the pandemic could have reduced weekly growth rate of cases and deaths by more than 10 percentage points in late April and 34% (95% CI: 19–47%) fewer deaths nationally by end of May|
|Leffler90||Population-based intervention with trend analysis||169 countries||January–May 2020||County population||Mask wearing by tradition, mandate, or recommendation||Duration of mask wearing by the public was negatively associated with per-capita mortality from COVID-19|
As of December 6, 2021
- Data were added from studies published since the last update. These studies address the association of mask wearing with new infections, including infections related to SARS-CoV-2 variants of concern. All of these studies demonstrated a benefit.
- A section was added on mask wearing among children.
- Moghadas SM, Fitzpatrick MC, Sah P, et al. The implications of silent transmission for the control of COVID-19 outbreaks. Proc Natl Acad Sci U S A. 2020;117(30):17513–17515.
- Johansson MA, Quandelacy TM, Kada S, et al. SARS-CoV-2 transmission from people without COVID-19 symptoms. JAMA Netw Open. 2021;4(1):e2035057.
- Lindsley W, Blachere F, Law B, Beezhold D, Noti J. Efficacy of face masks, neck gaiters and face shields for reducing the expulsion of simulated cough-generated aerosols. Aerosol Science and Technology. 2020;55:449–457.
- Fischer EP, Fischer MC, Grass D, Henrion I, Warren WS, Westman E. Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Sci Adv. 2020;6(36):eabd3083.
- Verma S, Dhanak M, Frankenfield J. Visualizing the effectiveness of face masks in obstructing respiratory jets. Phys Fluids (1994). 2020;32(6):061708.
- Bahl P, Bhattacharjee S, de Silva C, Chughtai AA, Doolan C, MacIntyre CR. Face coverings and mask to minimise droplet dispersion and aerosolisation: a video case study. Thorax. 2020;75(11):1024–1025.
- Davies A, Thompson KA, Giri K, Kafatos G, Walker J, Bennett A. Testing the efficacy of homemade masks: would they protect in an influenza pandemic? Disaster Med Public Health Prep. 2013;7(4):413–418.
- Leung NHL, Chu DKW, Shiu EYC, et al. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat Med. 2020;26(5):676–680.
- Bandiera L, Pavar G, Pisetta G, et al. Face coverings and respiratory tract droplet dispersion. R Soc Open Sci. 2020;7(12):201663.
- Alsved M, Matamis A, Bohlin R, et al. Exhaled respiratory particles during singing and talking. Aerosol Science and Technology. 2020;54(11):1245–1248.
- Asadi S, Wexler AS, Cappa CD, Barreda S, Bouvier NM, Ristenpart WD. Aerosol emission and superemission during human speech increase with voice loudness. Sci Rep. 2019;9(1):2348.
- Morawska L, Johnson GR, Ristovski ZD, et al. Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. Aerosol Sci. 2009;40(3):256–269.
- Abkarian M, Mendez S, Xue N, Yang F, Stone HA. Speech can produce jet-like transport relevant to asymptomatic spreading of virus. Proc Natl Acad Sci U S A. 2020;117(41):25237–25245.
- Ueki H, Furusawa Y, Iwatsuki-Horimoto K, et al. Effectiveness of face masks in preventing airborne transmission of SARS-CoV-2. mSphere. 2020;5(5):e00637-20.
- Rodriguez-Palacios A, Cominelli F, Basson AR, Pizarro TT, Ilic S. Textile masks and surface covers-a spray simulation method and a “Universal Droplet Reduction Model” against respiratory pandemics. Front Med (Lausanne). 2020;7:260.
- Viola IM, Peterson B, Pisetta G, et al. Face coverings, aerosol dispersion and mitigation of virus transmission risk. IEEE Open J Eng Med Biol. 2021;2:26–35.
- Adenaiye OO, Lai J, de Mesquita PJB, et al. Infectious SARS-CoV-2 in exhaled aerosols and efficacy of masks during early mild infection. Clin Infect Dis. 2021;doi:10.1093/cid/ciab797.
- 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 particles. Ann Occup Hyg. 2010;54(7):789–98.
- Long KD, Woodburn EV, Berg IC, Chen V, Scott WS. Measurement of filtration efficiencies of healthcare and consumer materials using modified respirator fit tester setup. PLoS One. 2020;15(10):e0240499.
- Konda A, Prakash A, Moss GA, Schmoldt M, Grant GD, Guha S. Aerosol filtration efficiency of common fabrics used in respiratory cloth masks. ACS Nano. 2020;14(5):6339–6347.
- O’Kelly E, Pirog S, Ward J, Clarkson PJ. Ability of fabric face mask materials to filter ultrafine particles at coughing velocity. BMJ Open. 2020;10(9):e039424.
- Aydin O, Emon B, Cheng S, Hong L, Chamorro LP, Saif MTA. Performance of fabrics for home-made masks against the spread of COVID-19 through droplets: A quantitative mechanistic study. Extreme Mech Lett. 2020;40:100924.
- Bhattacharjee S, Bahl P, Chughtai AA, MacIntyre CR. Last-resort strategies during mask shortages: optimal design features of cloth masks and decontamination of disposable masks during the COVID-19 pandemic. BMJ Open Respir Res. 2020;7(1):e000698.
- Maurer L, Peris D, Kerl J, Guenther F, Koehler D, Dellweg D. Community masks during the SARS-CoV-2 pandemic: filtration efficacy and air resistance. J Aerosol Med Pulm Drug Deliv. 2021;34(1):11–19.
- Hill WC, Hull MS, MacCuspie RI. Testing of commercial masks and respirators and cotton mask insert materials using SARS-CoV-2 virion-sized particulates: comparison of ideal aerosol filtration efficiency versus fitted filtration efficiency. Nano Lett. 2020;20(10):7642–7647.
- Whiley H, Keerthirathne TP, Nisar MA, White MAF, Ross KE. Viral filtration efficiency of fabric masks compared with surgical and N95 Masks. Pathogens. 2020;9(9):762.
- Hao W, Parasch A, Williams S, et al. Filtration performances of non-medical materials as candidates for manufacturing facemasks and respirators. Int J Hyg Environ Health. 2020;229:113582.
- 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(7):e2618.
- Chu DK, Akl EA, Duda S, et al. 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. Lancet. 2020;395(10242):1973–1987.
- Clase CM, Fu EL, Ashur A, et al. Forgotten technology in the COVID-19 pandemic: filtration properties of cloth and cloth masks-a narrative review. Mayo Clin Proc. 2020;95(10):2204–2224.
- Parlin AF, Stratton SM, Culley TM, Guerra PA. A laboratory-based study examining the properties of silk fabric to evaluate its potential as a protective barrier for personal protective equipment and as a functional material for face coverings during the COVID-19 pandemic. PLoS One. 2020;15(9):e0239531.
- Rothamer DA, Sanders S, Reindl D, Bertram TH. Strategies to minimize SARS-CoV-2 transmission in classroom settings: Combined impacts of ventilation and mask effective filtration efficiency. Sci Tech Built Environ. 2021;27(9):1181–1203.
- Mueller AV, Eden MJ, Oakes JM, Bellini C, Fernandez LA. Quantitative method for comparative assessment of particle removal efficiency of fabric masks as alternatives to standard surgical masks for PPE. Matter. 2020;3(3):950–962.
- Clapp PW, Sickbert-Bennett EE, Samet JM, et al. Evaluation of cloth masks and modified procedure masks as personal protective equipment for the public during the COVID-19 pandemic. JAMA Intern Med. 2021;181(4):463–469.
- Brooks JT, Beezhold DH, Noti JD, et al. Maximizing fit for cloth and medical procedure masks to improve performance and reduce SARS-CoV-2 transmission and exposure, 2021. MMWR Morb Mortal Wkly Rep. 2021;70(7):254–257.
- Sickbert-Bennett EE, Samet JM, Prince SE, et al. Fitted filtration efficiency of double masking during the COVID-19 pandemic. JAMA Intern Med. 2021;181(8):1126–1128.
- Abaluck J, Kwong LH, Styczynski A, et al. Impact of community masking on COVID-19: a cluster-randomized trial in Bangladesh. Science. 2021; doi: 10.1126/science.abi9069.
- Payne DC, Smith-Jeffcoat SE, Nowak G, et al. SARS-CoV-2 infections and serologic responses from a sample of U.S. Navy service members – USS Theodore Roosevelt, April 2020. MMWR Morb Mortal Wkly Rep. 2020;69(23):714–721.
- Wang Y, Tian H, Zhang L, et al. Reduction of secondary transmission of SARS-CoV-2 in households by face mask use, disinfection and social distancing: a cohort study in Beijing, China. BMJ Glob Health. 2020;5(5):e002794.
- Nelson SB, Dugdale CM, Bilinski A, Cosar D, Pollock NR, Ciaranello A. Prevalence and risk factors for in-school transmission of SARS-CoV-2 in Massachusetts K-12 public schools, 2020-2021. medRxiv. 2021; doi.org/10.1101/2021.09.22.21263900.
- Doung-Ngern P, Suphanchaimat R, Panjangampatthana A, et al. Case-control study of use of personal protective measures and risk for Severe Acute Respiratory Syndrome Coronavirus 2 infection, Thailand. Emerg Infect Dis. 2020;26(11):2607–2616.
- Jehn M, McCullough JM, Dale AP, Gue M, Eller B, Cullen T, Scott SE. Association between K–12 school mask policies and school-associated COVID-19 outbreaks — Maricopa and Pima Counties, Arizona, July–August 2021. MMWR Morb Mortal Wkly Rep. 2021; 70(39);1372–1373.
- Budzyn SE, Panaggio MJ, Parks SE, Papazian M, Magid J, Eng M, Barrios LC. Pediatric COVID-19 cases in counties with and without school mask requirements — United States, July 1–September 4, 2021. MMWR Morb Mortal Wkly Rep. 2021; 70(39);1377–1378.
- Hendrix MJ, Walde C, Findley K, Trotman R. Absence of apparent transmission of SARS-CoV-2 from two stylists after exposure at a hair salon with a universal face covering policy – Springfield, Missouri, May 2020. MMWR Morb Mortal Wkly Rep. 2020;69(28):930-932.
- Schwartz KL, Murti M, Finkelstein M, et al. Lack of COVID-19 transmission on an international flight. CMAJ. 2020;192(15):E410.
- Freedman DO, Wilder-Smith A. In-flight transmission of SARS-CoV-2: a review of the attack rates and available data on the efficacy of face masks. J Travel Med. 2020;27(8):taaa178.
- Wang X, Ferro EG, Zhou G, Hashimoto D, Bhatt DL. Association between universal masking in a health care system and SARS-CoV-2 positivity among health care workers. JAMA. 2020;324(7):703–704.
- Mitze T, Kosfeld R, Rode J, Wälde K. Face masks considerably reduce COVID-19 cases in Germany. Proc Natl Acad Sci U S A. 2020;117(51):32293–32301.
- Gallaway MS, Rigler J, Robinson S, et al. Trends in COVID-19 incidence after implementation of mitigation measures – Arizona, January 22-August 7, 2020. MMWR Morb Mortal Wkly Rep. 2020;69(40):1460–1463.
- Van Dyke ME, Rogers TM, Pevzner E, et al. Trends in county-level COVID-19 incidence in counties with and without a mask mandate – Kansas, June 1-August 23, 2020. MMWR Morb Mortal Wkly Rep. 2020;69(47):1777–1781.
- Lyu W, Wehby GL. Community use of face masks and COVID-19: evidence from a natural experiment of state mandates in the US. Health Aff (Millwood). 2020;39(8):1419–1425.
- Hatzius J, Struyven D, Rosenberg I. Face masks and GDP. Updated June 29, 2020. Accessed July 8, 2020. https://www.goldmansachs.com/insights/pages/face-masks-and-gdp.html
- Karaivanov A, Lu SE, Shigeoka H, Chen C, Pamplona S. Face masks, public policies and slowing the spread of COVID-19: evidence from Canada. J Health Econ. 2021;78:102475.
- Joo H, Miller GF, Sunshine G, et al. Decline in COVID-19 hospitalization growth rates associated with statewide mask mandates – 10 states, March-October 2020. MMWR Morb Mortal Wkly Rep. 2021;70(6):212–216.
- Chernozhukov V, Kasahara H, Schrimpf P. Causal impact of masks, policies, behavior on early COVID-19 pandemic in the U.S. J Econom. 2021;220(1):23–62.
- Guy GP Jr, Lee FC, Sunshine G, et al. Association of state-issued mask mandates and allowing on-premises restaurant dining with county-level COVID-19 case and death growth rates – United States, March 1-December 31, 2020. MMWR Morb Mortal Wkly Rep. 2021;70(10):350–354.
- Rader B, White LF, Burns MR, et al. Mask-wearing and control of SARS-CoV-2 transmission in the USA: a cross-sectional study. The Lancet Digital Health. 2021;3(3):e148–e157.
- Bundgaard H, Bundgaard JS, Raaschou-Pedersen DET, et al. Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers: a randomized controlled trial. Ann Intern Med. 2021;174(3):335–343.
- MacIntyre CR, Seale H, Dung TC, et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open. 2015;5(4):e006577.
- MacIntyre CR, Dung TC, Chughtai AA, Seale H, Rahman B. Contamination and washing of cloth masks and risk of infection among hospital health workers in Vietnam: a post hoc analysis of a randomised controlled trial. BMJ Open. 2020;10(9):e042045.
- Shein SL, Whitticar S, Mascho KK, Pace E, Speicher R, Deakins K. The effects of wearing facemasks on oxygenation and ventilation at rest and during physical activity. PLoS One. 2021;16(2):e0247414.
- Chan NC, Li K, Hirsh J. Peripheral oxygen saturation in older persons wearing nonmedical face masks in community settings. JAMA. 2020;324(22):2323–2324.
- Samannan R, Holt G, Calderon-Candelario R, Mirsaeidi M, Campos M. Effect of face masks on gas exchange in healthy persons and patients with chronic obstructive pulmonary disease. Ann Am Thorac Soc. 2021;18(3):541–544.
- Hopkins SR, Dominelli PB, Davis CK, et al. Face masks and the cardiorespiratory response to physical activity in health and disease. Ann Am Thorac Soc. 2021;18(3):399–407.
- Bar-On O, Gendler Y, Stafler P, et al. Effects of wearing facemasks during brisk walks: a COVID-19 dilemma. J Am Board Fam Med. 2021;34(4):798–801.
- Roberge RJ, Kim JH, Benson SM. Absence of consequential changes in physiological, thermal and subjective responses from wearing a surgical mask. Respir Physiol Neurobiol. 2012;181(1):29–35.
- Epstein D, Korytny A, Isenberg Y, et al. Return to training in the COVID-19 era: the physiological effects of face masks during exercise. Scand J Med Sci Sports. 2021;31(1):70–75.
- Shaw KA, Zello GA, Butcher SJ, Ko JB, Bertrand L, Chilibeck PD. The impact of face masks on performance and physiological outcomes during exercise: a systematic review and meta-analysis. Appl Physiol Nutr Metab. 2021;46(7):693–703.
- Slimani M, Miarka B, Znazen H, et al. Effect of a warm-up protocol with and without facemask-use against COVID-19 on cognitive function: a pilot, randomized counterbalanced, cross-sectional study. Int J Environ Res Public Health. 2021;18(11):5885.
- Schulte-Korne B, Hollmann W, Vassiliadis A, Predel HG. [Effects of surgical face masks on exercise performance and perceived exertion of exercise in well-trained healthy boys]. Wien Med Wochenschr. 2021;1–4.
- Person E, Lemercier C, Royer A, Reychler G. [Effect of a surgical mask on six minute walking distance]. Rev Mal Respir. Mar 2018;35(3):264–268.
- Driver S, Reynolds M, Brown K, et al. Effects of wearing a cloth face mask on performance, physiological and perceptual responses during a graded treadmill running exercise test. Br J Sports Med. 2021; bjsports-2020-103758.
- Lassing J, Falz R, Pokel C, et al. Effects of surgical face masks on cardiopulmonary parameters during steady state exercise. Sci Rep. 2020;10(1):22363.
- Fikenzer S, Uhe T, Lavall D, et al. Effects of surgical and FFP2/N95 face masks on cardiopulmonary exercise capacity. Clin Res Cardiol. 2020;109(12):1522–1530.
- Park SJ, Han HS, Shin SH, et al. Adverse skin reactions due to use of face masks: a prospective survey during the COVID-19 pandemic in Korea. J Eur Acad Dermatol Venereol. 2021;35(10):e628–e630.
- Chaiyabutr C, Sukakul T, Pruksaeakanan C, Thumrongtharadol J, Boonchai W. Adverse skin reactions following different types of mask usage during the COVID-19 pandemic. J Eur Acad Dermatol Venereol. 2021;35(3):e176–e178.
- Montero-Vilchez T, Cuenca-Barrales C, Martinez-Lopez A, Molina-Leyva A, Arias-Santiago S. Skin adverse events related to personal protective equipment: a systematic review and meta-analysis. J Eur Acad Dermatol Venereol. 2021;35(10):1994–2006.
- Techasatian L, Lebsing S, Uppala R, et al. The effects of the face mask on the skin underneath: a prospective survey during the COVID-19 pandemic. J Prim Care Community Health. 2020;11:2150132720966167.
- Smith J, Culler A, Scanlon K. Impacts of blood gas concentration, heart rate, emotional state, and memory in school‐age children with and without the use of facial coverings in school during the COVID‐19 pandemic. FASEB J. 2021;35(Suppl 1) doi:10.1096/fasebj.2021.35.S1.04955.
- Lubrano R, Bloise S, Testa A, et al. Assessment of respiratory function in infants and young children wearing face masks during the COVID-19 pandemic. JAMA Netw Open. 2021;4(3):e210414.
- Dost B, Kömürcü Ö, Bilgin S, Dökmeci H, Terzi Ö, Barış S. Investigating the effects of protective face masks on the respiratory parameters of children in the post-anesthesia care unit during the COVID-19 pandemic. J Perianesth Nurs. 2021; doi.org/10.1016/j.jopan.2021.02.004.
- Ammann P, Ulyte A, Haile SR, Puhan MA, Kriemler S, Radtke T. Perceptions towards mask use in school children during the SARS-CoV-2 pandemic: the Ciao Corona Study. medRxiv. 2021; doi.org/10.1101/2021.09.04.21262907.
- Gori M, Schiatti L, Amadeo MB. Masking emotions: face masks impair how we read emotions. Front Psychol. 2021;12:669432.
- Ruba AL, Pollak SD. Children’s emotion inferences from masked faces: implications for social interactions during COVID-19. PLoS One. 2020;15(12):e0243708.
- Singh L, Tan A, Quinn PC. Infants recognize words spoken through opaque masks but not through clear masks. Dev Sci. 2021;24(6):e13117.
- Sivaraman M, Virues-Ortega J, Roeyers H. Telehealth mask wearing training for children with autism during the COVID-19 pandemic. J Appl Behav Anal. 2021;54(1):70–86.
- Halbur M, Kodak T, McKee M, et al. Tolerance of face coverings for children with autism spectrum disorder. J Appl Behav Anal. 2021;54(2):600–617.
- Lillie MA, Harman MJ, Hurd M, Smalley MR. Increasing passive compliance to wearing a facemask in children with autism spectrum disorder. J Appl Behav Anal. 2021;54(2):582–599.
- Schneider J, Sandoz V, Equey L, Williams-Smith J, Horsch A, Bickle Graz M. The role of face masks in the recognition of emotions by preschool children. JAMA Pediatr. 2021;e214556.
- Leffler CT, Ing E, Lykins JD, Hogan MC, McKeown CA, Grzybowski A. Association of country-wide coronavirus mortality with demographics, testing, lockdowns, and public wearing of masks. Am J Trop Med Hyg. 2020;103(6):2400–2411.