Masks cannot prevent respiratory infections
This article will show how respiratory diseases are spread via dry aerosols produced during ordinary breathing. It will show how virions can stay airborne for many hours after they have dried whilst exiting the body. It will show that masks do not protect against bacterial or viral infections. It will show that masks can sometimes exacerbate disease and will cause ill-health.
Humidity and breath
The role of the nasal cavity in warming and humidifying the air we breathe has been long understood (Ingelstedt 1951) as too have the other structures in the upper respiratory tract like the pharynx, larynx and trachea that transport the air to the lungs (Ferron 1985). These controls over the humidity and temperature of the air we breathe is important because extremes in variation have been found to affect the mucosal function (Williams 1996) and thereby the health of the respiratory system.
We have all experienced the high humidity of the air we breathe out because we have all breathed on a cold mirror or glass to make it steam up and we have also seen our breath make clouds on a winter day as we walk outside. The humidity of the air we breathe out is constant and controlled by our bodies because it is saturated with water as we breathe in (Ferrus 1980; Daviska 1990). This saturated air is responsible for driving the spread of respiratory diseases (Ishmatov 2017) in what we call aerosols because it picks up virions from the infected lining of our respiratory tract.
The role of humidity in driving the spread of respiratory viruses was proven in 2010 when the incidences of flu was found to correlate with the humidity of the air (Shaman 2010).
The spread of respiratory diseases such as influenza is more commonplace when the outside air is cold and dry because the air we breathe out evaporates quickly to leave the dry virions that were within the droplets. These dry virions are able to remain in the air for extended periods of time. It is this quality of the air that enables the ‘flu season’ in the winter months (Kudo 2019) and infection can occur hours later far from an aerosol source even in air that is not being circulated (Bourouiba 2020).
Aerosols.
The term ‘aerosol’ refers to any small particles that are in the air. We all understand aerosol sprays that come in a can which we use to produce a fine mist of liquid aerosols into the air as air fresheners. In a similar way, aerosols are expelled by people when we breathe, speak, cough or sneeze (Tellier 2009). If a person is suffering from a respiratory infection, any infectious particles are also expelled with the liquid aerosols from our lungs and throat as we go about our daily lives. Viruses like influenza, rhinovirus and coronavirus use these aerosols to spread throughout the community.
Aerosol propagation from the infected has been measured at 76,000 course aerosols and 24,000 fine aerosols every hour and was 6.3 times more among people vaccinated in the current and previous season compared with having no vaccination in those two seasons. It was also found that viral load in nasal swabs, body temperature and history of asthma or smoking could not be used as an indicator of production of aerosolised viral shedding and that normal breathing produced “aerosol particles small enough to remain suspended in air and present a risk for airborne transmission” (Yan 2017).
There are many visualisations of aerosols being exhaled by people and they show how masks stop these aerosols but they do nothing to consider the transmission of viral diseases because they only visualise very large aerosols above 20 microns in size (Anfinrud 2020). It is generally understood that aerosols larger than 5 microns will fall to the ground quickly and that aerosols smaller than 5 microns will evaporate before reaching the ground and thereafter the virions will remain airborne for many hours (Morawaska 2006; Van Doremalen 2020). This is the reason that cold dry air in the winter is better suited for the transmission of respiratory diseases (Lester 1948; Shaman 2010). It was further found that raising the humidity in school classrooms decreased the number of influenza-like infections by over half (Reiman 2018) and high humidity or high temperatures were both found to denature coronavirus virions to make them unable to function and replicate (Morawaska 2006).
Although it is counter-intuitive, small aerosols contain a larger amount of virions than are found in large aerosols by between 3.4 times (Milton 2003) and 8.8 times as many (Fennelly 2020).
When we breathe in, large aerosols tend to remain trapped in the upper respiratory tract, the nose and throat areas, whereas small aerosols have the potential to be inhaled into the lower respiratory tract, the bronchi and alveoli in the lungs (Atkinson 2009; Eikenberry 2020), Therefore, it is thought that small aerosols are more contagious than large aerosols. Furthermore, it was found that 99.9% of aerosols expelled by cold-like sufferers were less than 5 microns in size (Lee 2019) and 87% of aerosols were less than 1 micron in size (Tellier 2009).
Additionally, a 2009 study by Zwart notes that "the action of a single virion is sufficient to cause disease." Furthermore, a 2020 study noted that it only takes between 10 and 15 mins for a virion to enter a cell and 7 to 8 hours before 600 to 700 new virions are released from that one cell to infect other cells in the body (Bar-On 2020). The incubation period before the onset of symptoms is approximately 6 days (Backer 2020) so the viral load within the infected person by the time they exhibit symptoms is around 16 with 51 zeros after it. These numbers are so large that they are hard to comprehend.
Therefore, it can be understood that for masks to help prevent infections they must be able to stop the smallest of particles that are made from dry virion clumps that are less than 1 micron in diameter and they must not allow even one virion to penetrate. Considering that small viruses are of a size that allows them to pass through condoms (Lytle 1997) it can be seen that masks are ineffective for this purpose.
Masks don’t stop infections
Many studies have been made but most investigated bacterial infections. The overall conclusion is that masks do not help prevent infections and in some cases have a negative affect by causing more infections than they prevent.
A 1975 study by Ritter, investigated wound infections in operating rooms by putting many ‘air settle plates’ into the operating rooms. It found a significant difference between operating rooms that were left unoccupied when compared to those that were used. It found no difference between the operating rooms that were used by people wearing masks and operating rooms that were used by people not wearing masks and concluded that masks did nothing to prevent the number of airborne contaminates and that “the wearing of a surgical face mask had no effect upon the overall operating room environmental contamination and probably work only to redirect the projectile effect of talking and breathing.”
A 1980 study by Ha’eri applied human albumin microspheres to the interior of surgical masks in 20 operations. At the end of each operation, wound washings were examined under the microscope. “Particle contamination of the wound was demonstrated in all experiments. Since the microspheres were not identified on the exterior of these face masks, they must have escaped around the mask edges and found their way into the wound.”
A 1981 study by Orr, investigated the use of surgical masks in theatre. Dr Orr was a surgeon in the Severalls Surgical Unit in Colchester. For six months, from March through August 1980, the surgeons and staff in that unit decided to see what would happen if they did not wear masks during surgeries by comparing the rate of surgical wound infections during the experiment time with the rate of wound infections from the previous four years.
They discovered, to their amazement, that when nobody wore masks during surgeries, the rate of wound infections was less than half what it was when everyone wore masks.
Their conclusion: “It would appear that minimum contamination can best be achieved by not wearing a mask at all” and that wearing a mask during surgery “is a standard procedure that could be abandoned.”
A 1983 study by Leaman, investigated mask use during cardiac catheterization and found that “the manner in which personnel and observers dress has no relationship to the incidence of infection” and there was “no correlation between the incidence of infection in those laboratories where personnel could work in ‘street clothing’ compared with those laboratories where all personnel were required to wear a scrub suit.” The study concluded that the majority of infections occurred because of contamination of the ‘cutdown site’ rather than from airborne pathogens.
A 1989 study by Laslett, found that caps and masks were not necessary during cardiac catheterization. “No infections were found in any patient, regardless of whether a cap or mask was used.”
A 1991 study by Tunevall, a general surgical team wore no masks in half of their surgeries for two years. After 1,537 operations performed with masks, the wound infection rate was 4.7%, while after 1,551 operations performed without masks, the wound infection rate was only 3.5%. The study concluded that masks may be used to protect staff from drops of blood which might be infected with hepatitis B or HIV but masks have not been proven to protect the patient from airborne infections.
A 2001 review by Skinner concluded that “the evidence for discontinuing the use of surgical face masks would appear to be stronger than the evidence available to support their continued use.” However, the study still recommended that surgical masks should be worn by the ‘scrub team’ but not by the rest of the operating room staff.
A 2001 study by Lahme, investigated the airborne germ count. It identified practical disadvantages of using facemasks for patients, in that doctor assessment of swallowing and breathing was hindered while patient anxiety and CO2 retention increased. The study found that “the patient mouthguard does not reduce the airborne germ concentration above the operating field and is therefore unnecessary according to the results of the present study.”
A 2001 study by Figueiredo, reported that in five years of doing peritoneal dialysis without masks, rates of peritonitis in their unit were no different than rates in hospitals where masks were worn. They concluded “that routine use of a face mask during CAPD bag exchange may be unnecessary.”
A 2008 study by van der Sande tested masks that filtered particles not viruses. The 1872V mask is the equivalent to the N95 mask and has a valve to allow air to escape unfiltered because it is only designed to protect the wearer from a contaminated environment. Therefore this type of mask will not prevent an infected person from spreading disease in any way whatsoever. The 1818 Tie-On surgical mask is a loose fitting mask that allows air to escape in every direction, therefore, this mask will not prevent the escape of dry virions and is not designed for that purpose. The 3M information sheet explains that these masks can filter bacteria and particulates that are in the air but they are not designed to filter viruses. The cloth masks they tested have been shown in many places to do nothing and only cause health problems for the wearer.
A 2008 study by Lau noted that perceptions related to human avian influenza were associated with influenza vaccine and mask use behaviours. This means that mask use can potentially be turned into opportunities of promoting desirable public health behaviours like vaccine uptake.
A 2009 systematic literature review by Bahli, found that infections decreased when masks were discarded and concluded that “it is still not clear that whether wearing surgical face masks harms or benefit the patients undergoing elective surgery.”
A 2009 study by Jacobs notes, N95-masked health-care workers (HCW) were significantly more likely to experience headaches. Face mask use in HCW was not demonstrated to provide benefit in terms of fewer cold symptoms or fewer infections.
A 2010 study by Sellden, found a lack of evidence supporting the use of masks, therefore, Karolinska University Hospital ceased using them in 2010 for anaesthesiologists and other non-scrubbed personnel in the operating room. “Our decision to no longer require routine surgical masks for personnel not scrubbed for surgery is a departure from common practice but the evidence to support this practice does not exist,”
A 2010 randomised controlled trial by Webster, investigated the use of facemasks during obstetric, gynaecological, general, orthopaedic, breast and urological surgeries performed on 827 patients. Masks were worn during half of the surgeries and no masks during the other half of surgeries. Surgical site infections occurred in 11.5% of the Mask group, and in only 9.0% of the No Mask group.
A 2010 review by Cowling noted that “there is some evidence to support the wearing of masks or respirators during illness to protect others” which occurred only when “the intervention was applied within 36 hours of symptom onset” but very little “data to support the use of masks or respirators to prevent becoming infected.” It further noted that mask-wearing was only associated with fewer infections when handwashing was also used.
A 2012 study by Wada, investigated the attitude of 3,000 Japanese people. They found that wearing a face mask in public may be associated with other personal hygiene practices and health behaviours among Japanese adults. Rather than preventing influenza itself, face mask use might instead be a marker of additional, positive hygiene practices and other favourable health behaviours in the same individuals like frequent hand washing, avoiding crowds, avoiding infected people, gargling and being vaccinated.
A 2012 review by Bin-Reza concluded, “none of the studies established a conclusive relationship between mask/respirator use and protection against influenza infection.” The study also noted that “some evidence suggests that mask use is best undertaken as part of a package of personal protection especially hand hygiene.”
A 2014 review by Lipp, found that “there was no statistically significant difference in infection rates between the masked and unmasked group in any of the trials.”
A 2014 review by Carøe, investigated 4 studies involving 6,006 patients and found that ““none of the four studies found a difference in the number of post-operative infections whether you used a surgical mask or not.”
A 2014 study by Salassa, investigated the necessity of scrubs, masks and head coverings in the operating room and concluded that “although there is some evidence that scrubs, masks, and head coverings reduce bacterial counts in the operating room, there is no evidence that these measures reduce the prevalence of surgical site infection.”
A 2015 review by Da Zhou, found that 20% of surgeons wore facemasks as respect for tradition even though they said they got in the way of proceedings by obscuring the surgeons vision by steaming up glasses or microscope equipment. The study concluded that “there is a lack of substantial evidence to support claims that facemasks protect either patient or surgeon from infectious contamination.”
A 2015 study by Macintyre, investigated 1,607 health care workers from 74 wards in 15 hospitals. The participants were randomised into 3 groups;-
1st group = medical masks
2nd group = cloth masks
3rd control group = standard practice use.
They found that the rates of all infection outcomes were highest in the cloth mask group. Additionally, laboratory-confirmed viral influenza-like illnesses were significantly higher in the cloth masks group compared with the medical masks group. Penetration of cloth masks by particles was almost 97% and medical masks 44%.
They concluded that caution should be taken when wearing cloth masks because “moisture retention, reuse of cloth masks and poor filtration may result in an increased risk of infection.” They went on to say “further research is needed to inform the widespread use of cloth masks globally. However, as a precautionary measure, cloth masks should not be recommended for health care workers, particularly in high-risk situations, and guidelines need to be updated.”
A 2016 review by Smith noted, In the meta-analysis of the clinical studies, we found no significant difference between N95 respirators and surgical masks in associated risk of (a) laboratory-confirmed respiratory infection, (b) influenza-like illness, or (c) reported work-place absenteeism.”
A 2016 review by Vincent, reviewed the same studies as Lipp (2014) and came to the same conclusion, “there was no statistically significant difference in infection rates between the masked and unmasked group in any of the trials.”
A 2017 study by Offeddu noted, masks prevented bacterial infections but not viral infections.
A 2020 article by Van Doremalen published in the New England Journal of Medicine explains how the virus stays airborne in aerosols less than 5 microns for up to 3 hours.
A 2020 study by Long, reviewed 6 random controlled trials involving 9,171 participants and found that there was no significant difference between wearing an N95 or a paper surgical mask for stopping the transmission of viral infections and they should only be used in high-risk situations.
A 2020 review of the literature by Xiao identified 10 studies investigating the use of facemasks and concluded that “the evidence from random controlled trials suggested that the use of face masks either by infected persons or by uninfected persons does not have a substantial effect on influenza transmission.”
A 2020 study by Klompas, explains that “Public health authorities define a significant exposure to Covid-19 as face-to-face contact within 6 feet with a patient with symptomatic Covid-19 that is sustained for at least a few minutes (and some say more than 10 minutes or even 30 minutes).” It then goes on to say “the chance of catching Covid-19 from a passing interaction in a public space is therefore minimal. In many cases, the desire for wide-spread masking is a reflexive reaction to anxiety over the pandemic.”
It further clarifies the understanding by noting “a mask will not protect providers caring for a patient with active Covid-19 if it’s not accompanied by meticulous hand hygiene, eye protection, gloves, and a gown. A mask alone will not prevent health care workers with early Covid-19 from contaminating their hands and spreading the virus to patients and colleagues.”
It is therefore common knowledge that wearing a mask by the general public is not necessary in almost all situations and also provides no protection when it is necessary.
A 2020 article by Rancourt, used information from many science studies to ascertain the main transmission path is long-residence-time aerosol particles that are smaller than 2.5 microns. These particles are too small to be blocked by masks. It also notes that because an infection can occur from just one virion and up to 100 virions are suspended in each of the smallest droplets of spit, it is impossible for masks to stop the spread of viral infections by containing only large droplets of spit. The article shows deaths from respiratory diseases in graph form and it can be seen that they are seasonal and is proven to be directly connected to the humidity of the surrounding air. It is the humidity of the air that drives virus epidemics and wearing masks or shaking hands has little to no effect. Once the spread of viruses is understood it becomes apparent why no study has ever found a benefit from wearing a mask or respirator.
A 2020 study by Leung investigated aerosols from influenza, rhinovirus and coronavirus sufferers. Leung found for rhinovirus sufferers, masks did not change the virus particles exhaled. For Influenza sufferers, masks prevented large aerosols but not small aerosols. For coronavirus, masks prevented small and large aerosols. The filtering properties of the masks cannot change depending on the health condition of the person being tested and so these findings are confusing. How is it possible for masks to only filter aerosols, small and large, exhaled by coronavirus sufferers and only large for influenza sufferers while not filtering either small or large for rhinovirus sufferers? Unfortunately the study did not obtain controls without masks from each of the subjects before they donned a mask. It may have been that the subjects tested for coronavirus were not making small or large aerosols because of the nature of coronavirus presenting with a dry cough.
Masks are harmful to your health.
A 1981 study by Aldman found that full-face motor-cycle helmets interfered with gas exchange and increased the CO2 levels to above 3% (30,000 ppm) and exercise (physical work of riding motor-bike) increased the CO2 even further. Dead space are areas in which the air is not refreshed due to lack of circulation and it is these areas that retain higher CO2 levels and this effect is accentuated by physical exertion.
The study concludes that CO2 levels are too high in Motor-bike helmets and advises riders to open their visor when at red lights, leave the visor slightly open while riding, moped riders should not wear full-face helmets and if a rider has an accident the visor should be raised immediately because “high concentration of CO2 in an unconscious person is extremely dangerous to the bra1n functions.”
A 2004 study by Kao investigated the use of N95 masks by 39 patients for 4 hours during kidney dialysis. They found oxygen saturation levels dropped, respiratory rate increased as did chest discomfort and patients also suffered respiratory distress.
A 2008 study by Beder, recorded that “researchers examined the blood oxygen levels in 53 surgeons using an oximeter. They measured blood oxygenation before surgery as well as at the end of surgeries. The researchers found that the mask reduced the blood oxygen levels (pa02) significantly. The longer the duration of wearing the mask, the greater the fall in blood oxygen levels.”
A 2014 study by Zhu, found that about a third of the workers developed headaches with the use of a mask, most had pre-existing headaches that were worsened by the mask-wearing, and 60% required pain medications for relief. As to the cause of the headaches, while straps and pressure from the mask could be causative, the bulk of the evidence points toward hypoxia and/or hypercapnia as the cause. That is, a reduction in blood oxygenation (hypoxia) or an elevation in blood C02 (hypercapnia).
A 2015 study by Tong, noted that “"breathing through N95 mask materials have been shown to impede gaseous exchange and impose an additional workload on the metabolic system of pregnant healthcare workers, and this needs to be taken into consideration in guidelines for respirator use. The benefits of using N95 mask to prevent serious emerging infectious diseases should be weighed against potential respiratory consequences associated with extended N95 respirator usage."
A 2020 study by Hua investigated the condition of the skin that was covered by the mask. It found that skin characteristics changed to produce more sebum in both covered and uncovered skin. It also found in the area that was covered by the mask that the skin became more hydrated and additional water loss occurred along with changes in pH and redness. These effects were more pronounced with the N95 masks and they were similar to the changes found in the skin of babies who wear nappies.
A 2020 study by Fikenzer found that while masks made some difference to reduced gas exchange under resting conditions in that the “forced vital capacity” and “forced expiratory flow” was reduced the main difference was found to occur during the “incremental exertion test” where a large reduction in performance measures was recorded.
The measurements show that surgical masks, and to a greater extent N95 masks, reduce the maximum power. Pmax (Watt) depends on energy consumption and the maximum oxygen uptake (VO2max). The effect of the masks was most pronounced on VO2max. Since the cardiac output was similar between the conditions, the reduction of Pmax was primarily driven by the observed reduction of the arterio-venous oxygen content. Therefore, the primary effect of the face masks on physical performance in healthy individuals is driven by the reduction of pulmonary function.
A 2020 study by Chandrasekaran identifies sedentary lifestyles as being detrimental to health by increasing the risk of cardiometabolic diseases such as obesity, coronary artery diseases, hypertension and cancer. The study identifies many factors associated with exercise that “might be protective against Covid-19 acute respiratory distress syndrome.” This study also notes that facemasks “induces a hypercapnic/hypoxia environment, inadequate Oxygen (O2) and Carbon dioxide (CO2) exchange and that “this acidic environment both at the alveolar and blood vessels level induces numerous physiological alterations when exercising with facemasks: 1) Metabolic shift; 2) cardiorespiratory stress; 3) excretory system altercations; 4) Immune mechanism; 5) Brain and nervous system.” It also notes that “individuals exercising with a mask would have physiological effects similar to a Chronic Obstructive Pulmonary Disease (COPD) person exercising such as discomfort, fatigue, dizziness, headache, shortness of breath, muscular weakness and drowsiness.” It explains that “this acidic environment would unload O2 faster at the muscle level, but due to higher heart rate and reduced affinity at the alveolar junction, the partial pressure of O2 would substantially fall, creating a hypoxic environment for all vital organs.” Furthermore, it found that “the bitter reality is that masks increase the risk of more in-depth respiratory tract infections” because “surgical masks trap the droplets containing the virus inside, increasing rather than reducing the risk of infection.” The study concludes that “exercising with facemasks might increase pathophysiological risks of underlying chronic disease, especially cardiovascular and metabolic risks.” “The hypercapnic hypoxia associated with N95 respirators during exercises induces acidic environment which in turn affects the immune, circulatory and metabolic systems” and “may exacerbate the pathology of underlying chronic diseases” while also causing “depression and anxiety induced by poor oxygenation and vasodilatory status.” It is also noted that “no evidence has shown N95 is effective in preventing the virus.”
Comparing masks
A 2009 study by Loeb found no difference between surgical masks and N95 respirators in preventing influenza infection.
A 2017 study by Offeddu noted, N95 masks supplied superior protection when compared to surgical masks at preventing respiratory infections in health care workers but only when the N95 mask was fitted professionally.
A 2019 study by Radonovich, found no difference between surgical masks and N95 respirators in preventing influenza infection.
A 2020 review of the literature by Chu found that N95 respirators gave better results than surgical masks and both N95 and surgical masks gave better protection than single layer cloth masks. However, the study also noted that, “no intervention, even when properly used, was associated with complete protection from infection.”
Conclusion
It has been shown that viruses travel in aerosols that are expelled during normal breathing. The aerosols dry quickly as we breathe out to leave a nuclei containing hundreds of virions. The virions are able to remain suspended in the air for many hours. It only takes one virion to start an infection.
Masks are not able to stop bacterial infections even though bacteria are far larger than viruses. In some cases masks have been shown to encourage infections and it is thought that they just alter the trajectory of infectious organisms rather than stop their propagation.
Masks cause many ill effects including, fatigue, dizziness, headache, shortness of breath, muscular weakness, drowsiness, hypoxia, hypercapnia and skin rashes. While exercising with a mask causes metabolic shift, cardiorespiratory stress and alterations in the excretory system, immune mechanism, brain and nervous system and physiological effects similar to a Chronic Obstructive Pulmonary Disease (COPD).
An N95 is only better than a simple surgical mask when it is fitted professionally and even then does not prevent infections without the use of other interventions, like hand washing and isolation.
References:
Aldrnan, B., Nygren, A., Sporrong, A. and Astrand, I., 1981. Carbon dioxide retention inside motor-cycle helmets. Available from http://www.ircobi.org/wordpress/downloads/irc1981/pdf_files/1981_11.pdf
Anfinrud, P., Stadnytskyi, V., Bax, C.E. and Bax, A., 2020. Visualizing speech-generated oral fluid droplets with laser light scattering. New England Journal of Medicine. Available from https://www.nejm.org/doi/pdf/10.1056/NEJMc2007800
Atkinson, J., Chartier, Y., Pessoa‐Silva, C.L., Jensen, P., Li, Y. and Seto, W.H., 2009. Respiratory droplets. World Health Organization. Available from https://www.ncbi.nlm.nih.gov/books/NBK143281/
Backer, J.A., Klinkenberg, D. and Wallinga, J., 2020. Incubation period of 2019 novel coronavirus (2019-nCoV) infections among travellers from Wuhan, China, 20–28 January 2020. Eurosurveillance, 25(5), p.2000062. Available from https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2020.25.5.2000062;jsessionid=kqIIleuMHsxDmfRKe4Ey6p5r.i-0b3d9850f4681504f-ecdclive
Bahli, Z.M., 2009. Does evidence based medicine support the effectiveness of surgical facemasks in preventing postoperative wound infections in elective surgery. J Ayub Med Coll Abbottabad, 21(2), pp.166-70. Available from http://www.ayubmed.edu.pk/JAMC/PAST/21-2/Zahid.pdf
Bar-On, Y.M., Flamholz, A., Phillips, R. and Milo, R., 2020. Science Forum: SARS-CoV-2 (COVID-19) by the numbers. Elife, 9, p.e57309. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7224694/?fbclid=IwAR3uI_FJ6iCHhy4HFa5nEyHC3ZxmNX1eWWclRql5tJZk-3fD057-e_I7XDs
Bourouiba, L. (2020). Turbulent gas clouds and respiratory pathogen emissions: potential implications for reducing transmission of COVID-19. Jama, 323(18), pp.1837-1838. Available from https://jamanetwork.com/journals/jama/fullarticle/2763852
Beder, A., Büyükkoçak, Ü., Sabuncuoğlu, H., Keskil, Z.A. and Keskil, S., 2008. Preliminary report on surgical mask induced deoxygenation during major surgery. Neurocirugia, 19(2), pp.121-126. Available from https://www.ratical.org/PandemicParallaxView/Bader-SurgMaskIndDeoxygen.pdf
bin‐Reza, F., Lopez Chavarrias, V., Nicoll, A. and Chamberland, M.E., 2012. The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence. Influenza and other respiratory viruses, 6(4), pp.257-267. Available from https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1750-2659.2011.00307.x
Carøe, T., 2014. Dubious effect of surgical masks during surgery. Ugeskrift for laeger, 176(27), pp.V09130564-V09130564. Available from https://europepmc.org/article/med/25294675
Chandrasekaran, B. and Fernandes, S., 2020. “Exercise with facemask; Are we handling a devil's sword?”–A physiological hypothesis. Medical hypotheses, 144, p.110002. Available from https://www.sciencedirect.com/science/article/pii/S0306987720317126
Chu, D.K., Akl, E.A., Duda, S., Solo, K., Yaacoub, S., Schünemann, H.J., El-harakeh, A., Bognanni, A., Lotfi, T., Loeb, M. and Hajizadeh, A., 2020. 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. The Lancet. Available from https://www.sciencedirect.com/science/article/pii/S0140673620311429
Cowling, B.J., Zhou, Y.D.K.M., Ip, D.K.M., Leung, G.M. and Aiello, A.E., 2010. Face masks to prevent transmission of influenza virus: a systematic review. Epidemiology & infection, 138(4), pp.449-456. Available from https://www.researchgate.net/profile/Allison_Aiello/publication/41110777_Face_masks_to_prevent_transmission_of_influenza_virus_A_systematic_review/links/563cc1f508ae34e98c4ab614.pdf
Da Zhou, C., Sivathondan, P. and Handa, A., 2015. Unmasking the surgeons: the evidence base behind the use of facemasks in surgery. Journal of the Royal Society of Medicine, 108(6), pp.223-228. Available from https://journals.sagepub.com/doi/pdf/10.1177/0141076815583167
Daviskas, E.V.A.N.G.E.L.I.A., Gonda, I.G.O.R. and Anderson, S.D., 1990. Mathematical modeling of heat and water transport in human respiratory tract. Journal of Applied Physiology, 69(1), pp.362-372. Available from https://journals.physiology.org/doi/abs/10.1152/jappl.1990.69.1.362
Eikenberry, S.E., Mancuso, M., Iboi, E., Phan, T., Eikenberry, K., Kuang, Y., Kostelich, E. and Gumel, A.B., 2020. To mask or not to mask: Modeling the potential for face mask use by the general public to curtail the COVID-19 pandemic. Infectious Disease Modelling. Available from https://www.sciencedirect.com/science/article/pii/S2468042720300117
Fennelly, K.P., 2020. Particle sizes of infectious aerosols: implications for infection control. The Lancet Respiratory Medicine. Available from https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30323-4/fulltext
Ferron, G.A., Haider, B. and Kreyling, W.G., 1985. A method for the approximation of the relative humidity in the upper human airways. Bulletin of mathematical biology, 47(4), pp.565-589. Available from https://www.sciencedirect.com/science/article/abs/pii/S0092824085900229
Ferrus, L., Guenard, H., Vardon, G. and Varene, P., 1980. Respiratory water loss. Respiration physiology, 39(3), pp.367-381. Available from https://www.sciencedirect.com/science/article/abs/pii/0034568780900675
Figueiredo, A.E., de Figueiredo, C.P. and Od Avila, D., 2001. Bag exchange in continuous ambulatory peritoneal dialysis without use of a face mask: experience of five years. Advances in peritoneal dialysis, 17, pp.98-100. Available from http://www.advancesinpd.com/adv01/21Figueiredo.htm
Fikenzer, S., Uhe, T., Lavall, D., Rudolph, U., Falz, R., Busse, M., Hepp, P. and Laufs, U., 2020. Effects of surgical and FFP2/N95 face masks on cardiopulmonary exercise capacity. Clinical Research in Cardiology, pp.1-9. Available from https://link.springer.com/article/10.1007/s00392-020-01704-y?fbclid=IwAR2efCeG691ekjaZyuy8w26-m8DNIPjjCDy2sa1uBlv0EwWbcgC9l5ak8Sk
Ha'Eri, G.B. and Wiley, A.M., 1980. The efficacy of standard surgical face masks: an investigation using" tracer particles". Clinical orthopaedics and related research, (148), pp.160-162. Available from https://europepmc.org/article/med/7379387
Hua, W., Zuo, Y., Wan, R., Xiong, L., Tnag, J., Zou, L., Shu, X. and Li, L., 2020. Short‐term Skin Reactions Following Use of N95 Respirators and Medical Masks. Contact Dermatitis. Available from https://pubmed.ncbi.nlm.nih.gov/32406064/
Ingelstedt, S. and Ivstam, B., 1951. Study in the humidifying capacity of the nose. Acta oto-laryngologica, 39(4), pp.286-290. Available from https://www.tandfonline.com/doi/abs/10.3109/00016485109119255?journalCode=ioto20
Ishmatov, A.N., 2017. On the connection between supersaturation in the upper airways and «humid-rainy» and «cold-dry» seasonal patterns of influenza (No. e2859v1). PeerJ Preprints. Available from https://peerj.com/preprints/2859.pdf
Jacobs, J.L., Ohde, S., Takahashi, O., Tokuda, Y., Omata, F. and Fukui, T., 2009. Use of surgical face masks to reduce the incidence of the common cold among health care workers in Japan: a randomized controlled trial. American journal of infection control, 37(5), pp.417-419. Available from https://pubmed.ncbi.nlm.nih.gov/19216002/
Kao, T.W., Huang, K.C., Huang, Y.L., Tsai, T.J., Hsieh, B.S. and Wu, M.S., 2004. The physiological impact of wearing an N95 mask during hemodialysis as a precaution against SARS in patients with end-stage renal disease. Journal of the Formosan Medical Association= Taiwan yi zhi, 103(8), pp.624-628. Available from https://pubmed.ncbi.nlm.nih.gov/15340662/
Klompas, M., Morris, C.A., Sinclair, J., Pearson, M. and Shenoy, E.S., 2020. Universal masking in hospitals in the Covid-19 era. New England Journal of Medicine, 382(21), p.e63. Available from
Kudo, E., Song, E., Yockey, L.J., Rakib, T., Wong, P.W., Homer, R.J. and Iwasaki, A., 2019. Low ambient humidity impairs barrier function and innate resistance against influenza infection. Proceedings of the National Academy of Sciences, 116(22), pp.10905-10910. Available from https://www.pnas.org/content/116/22/10905/
Leaman, D.M. and Zelis, R.F., 1983. What is the appropriate “dress code” for the cardiac catheterization laboratory?. Catheterization and cardiovascular diagnosis, 9(1), pp.33-38. Available from https://onlinelibrary.wiley.com/doi/abs/10.1002/ccd.1810090106
Lahme, T., Jung, W.K., Wilhelm, W. and Larsen, R., 2001. Patientenmundschutz bei Regionalanästhesien Hygienische Notwendigkeit oder entbehrliches Ritual?. Der Anaesthesist, 50(11), pp.846-851. Available from https://link.springer.com/article/10.1007%2Fs00101-001-0229-x
Laslett, L.J. and Sabin, A., 1989. Wearing of caps and masks not necessary during cardiac catheterization. Catheterization and cardiovascular diagnosis, 17(3), pp.158-160. Available fromhttps://onlinelibrary.wiley.com/doi/abs/10.1002/ccd.1810170306
Lau, J.T.F., Kim, J.H., Tsui, H.Y. and Griffiths, S., 2008. Perceptions related to bird-to-human avian influenza, influenza vaccination, and use of face mask. Infection, 36(5), pp.434-443. Available from https://link.springer.com/article/10.1007/s15010-008-7277-y
Lee, J., Yoo, D., Ryu, S., Ham, S., Lee, K., Yeo, M., Min, K. and Yoon, C., 2018. Quantity, size distribution, and characteristics of cough-generated aerosol produced by patients with an upper respiratory tract infection. Aerosol and Air Quality Research, 19(4), pp.840-853. Available from https://aaqr.org/articles/aaqr-18-01-oa-0031.pdf
Lester Jr, W., 1948. The influence of relative humidity on the infectivity of air-borne influenza A virus (PR8 strain). The Journal of experimental medicine, 88(3), pp.361-368. Available from https://rupress.org/jem/article/88/3/361/5171/THE-INFLUENCE-OF-RELATIVE-HUMIDITY-ON-THE
Leung, N.H., Chu, D.K., Shiu, E.Y., Chan, K.H., McDevitt, J.J., Hau, B.J., Yen, H.L., Li, Y., Ip, D.K., Peiris, J.M. and Seto, W.H., 2020. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nature medicine, 26(5), pp.676-680. Available from https://www.nature.com/articles/s41591-020-0843-2#Tab1
Lipp, A. and Edwards, P., 2002. Disposable surgical face masks for preventing surgical wound infection in clean surgery. Cochrane Database of Systematic Reviews, (1). Available from https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD002929/epdf/full
Loeb, M., Dafoe, N., Mahony, J., John, M., Sarabia, A., Glavin, V., Webby, R., Smieja, M., Earn, D.J., Chong, S. and Webb, A., 2009. Surgical mask vs N95 respirator for preventing influenza among health care workers: a randomized trial. Jama, 302(17), pp.1865-1871. Available from https://jamanetwork.com/journals/jama/fullarticle/184819
Long, Y., Hu, T., Liu, L., Chen, R., Guo, Q., Yang, L., Cheng, Y., Huang, J. and Du, L., 2020. Effectiveness of N95 respirators versus surgical masks against influenza: a systematic review and meta‐analysis. Journal of Evidence‐Based Medicine, 13(2), pp.93-101. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7228345/pdf/JEBM-9999-na.pdf
LYTLE, D.C., Routson, L.B., Seaborn, G.B., Dixon, L.G., Bushar, H.F. and CYR, H.W., 1997. An in vitro evaluation of condoms as barriers to a small virus. Sexually transmitted diseases, 24(3), pp.161-164. Available from https://journals.lww.com/stdjournal/Fulltext/1997/03000/An_In_Vitro_Evaluation_of_Condoms_as_Barriers_to_a.7.aspx
MacIntyre, C.R., Seale, H., Dung, T.C., Hien, N.T., Nga, P.T., Chughtai, A.A., Rahman, B., Dwyer, D.E. and Wang, Q., 2015. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ open, 5(4), p.e006577. Available from https://bmjopen.bmj.com/content/bmjopen/5/4/e006577.full.pdf
Milton, D.K., Fabian, M.P., Cowling, B.J., Grantham, M.L. and McDevitt, J.J., 2013. Influenza virus aerosols in human exhaled breath: particle size, culturability, and effect of surgical masks. PLoS Pathog, 9(3), p.e1003205. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3591312/
Morawska, L., 2005. Droplet fate in indoor environments, or can we prevent the spread of infection?. In Proceedings of Indoor Air 2005: the 10th International Conference on Indoor Air Quality and Climate (pp. 9-23). Springer. Available from https://onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0668.2006.00432.x
Offeddu, V., Yung, C.F., Low, M.S.F. and Tam, C.C., 2017. Effectiveness of masks and respirators against respiratory infections in healthcare workers: a systematic review and meta-analysis. Clinical Infectious Diseases, 65(11), pp.1934-1942. Available from https://academic.oup.com/cid/article/65/11/1934/4068747?fbclid=IwAR2Qw1QboPb5aT4RyeyEyAJBGlq1DfrIpyd_aXFjxeuI-SoN3wWm1fddTb8
Orr, N.W., 1981. Is a mask necessary in the operating theatre?. Annals of the Royal College of Surgeons of England, 63(6), p.390. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2493952/pdf/annrcse01509-0009.pdf
Radonovich, L.J., Simberkoff, M.S., Bessesen, M.T., Brown, A.C., Cummings, D.A., Gaydos, C.A., Los, J.G., Krosche, A.E., Gibert, C.L., Gorse, G.J. and Nyquist, A.C., 2019. N95 respirators vs medical masks for preventing influenza among health care personnel: a randomized clinical trial. Jama, 322(9), pp.824-833. Available from https://jamanetwork.com/journals/jama/article-abstract/2749214
Rancourt, D.G., 2017. The Science is Conclusive: Masks and Respirators do NOT Prevent Transmission of Viruses. Clinical Infectious Diseases, 65(11). Available from https://www.sott.net/article/434796-The-Science-is-Conclusive-Masks-and-Respirators-do-NOT-Prevent-Transmission-of-Viruses?fbclid=IwAR3Mb9yrhwLi1UQXkwgvwdclCfgQSsPEeTyEWyaFddM1ACMzPo0F4sVn82g
Reiman, J.M., Das, B., Sindberg, G.M., Urban, M.D., Hammerlund, M.E., Lee, H.B., Spring, K.M., Lyman-Gingerich, J., Generous, A.R., Koep, T.H. and Ewing, K., 2018. Humidity as a non-pharmaceutical intervention for influenza A. PloS one, 13(9), p.e0204337. Available from https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0204337
Ritter, M.A., Eitzen, H., French, M.L. and Hart, J.B., 1975. The operating room environment as affected by people and the surgical face mask. Clinical Orthopaedics and related research, (111), pp.147-150. Available from https://journals.lww.com/clinorthop/Citation/1975/09000/The_Operating_Room_Environment_as_Affected_by.20.aspx
Salassa, T.E. and Swiontkowski, M.F., 2014. Surgical attire and the operating room: role in infection prevention. JBJS, 96(17), pp.1485-1492. Available from https://journals.lww.com/jbjsjournal/Abstract/2014/09030/Surgical_Attire_and_the_Operating_Room__Role_in.11.aspx
Sellden, E. and Hemmings, H.C., 2010. Is routine use of a face mask necessary in the operating room?. The Journal of the American Society of Anesthesiologists, 113(6), pp.1447-1447. Available from https://pubs.asahq.org/anesthesiology/article/113/6/1447/9572/Is-Routine-Use-of-a-Face-Mask-Necessary-in-the
Shaman, J., Pitzer, V.E., Viboud, C., Grenfell, B.T. and Lipsitch, M., 2010. Absolute humidity and the seasonal onset of influenza in the continental United States. PLoS Biol, 8(2), p.e1000316. Available from https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1000316
Skinner, M.W. and Sutton, B.A., 2001. Do anaesthetists need to wear surgical masks in the operating theatre? A literature review with evidence-based recommendations. Anaesthesia and intensive care, 29(4), pp.331-338. Available from https://journals.sagepub.com/doi/pdf/10.1177/0310057X0102900402
Smith, J.D., MacDougall, C.C., Johnstone, J., Copes, R.A., Schwartz, B. and Garber, G.E., 2016. Effectiveness of N95 respirators versus surgical masks in protecting health care workers from acute respiratory infection: a systematic review and meta-analysis. Cmaj, 188(8), pp.567-574. Available fromhttps://www.cmaj.ca/content/cmaj/188/8/567.full.pdf
Tellier, R., 2009. Aerosol transmission of influenza A virus: a review of new studies. Journal of the Royal Society Interface, 6(suppl_6), pp.S783-S790. Available from https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2009.0302.focus
Tong, P.S.Y., Kale, A.S., Ng, K., Loke, A.P., Choolani, M.A., Lim, C.L., Chan, Y.H., Chong, Y.S., Tambyah, P.A. and Yong, E.L., 2015. Respiratory consequences of N95-type Mask usage in pregnant healthcare workers—a controlled clinical study. Antimicrobial Resistance & Infection Control, 4(1), pp.1-10. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4647822/pdf/13756_2015_Article_86.pdf
Tunevall, T.G., 1991. Postoperative wound infections and surgical face masks: a controlled study. World journal of surgery, 15(3), pp.383-387. Available from https://link.springer.com/article/10.1007/BF01658736
van der Sande, M., Teunis, P. and Sabel, R., 2008. Professional and home-made face masks reduce exposure to respiratory infections among the general population. PloS one, 3(7), p.e2618. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440799/?fbclid=IwAR13coY1ECyXO0GDJrXiROwiX--5P8D4-ZvvvBx52bZSfh-LYdSI3OjrlhY
Van Doremalen, N., Bushmaker, T., Morris, D.H., Holbrook, M.G., Gamble, A., Williamson, B.N., Tamin, A., Harcourt, J.L., Thornburg, N.J., Gerber, S.I. and Lloyd-Smith, J.O., 2020. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. New England Journal of Medicine, 382(16), pp.1564-1567. Available from https://www.nejm.org/doi/full/10.1056/nejmc2004973?fbclid=IwAR0zSqumybAAjpHNkctQVw9YLXMkI9HClhVZwlwB6MWXs8jcvVql8vWsneA
Vincent, M. and Edwards, P., 2016. Disposable surgical face masks for preventing surgical wound infection in clean surgery. Cochrane Database of Systematic Reviews, (4). Available from https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD002929.pub3/epdf/full
Wada, K., Oka-Ezoe, K. and Smith, D.R., 2012. Wearing face masks in public during the influenza season may reflect other positive hygiene practices in Japan. BMC Public Health, 12(1), p.1065. Available from https://link.springer.com/article/10.1186/1471-2458-12-1065
Webster, J., Croger, S., Lister, C., Doidge, M., Terry, M.J. and Jones, I., 2010. Use of face masks by non‐scrubbed operating room staff: a randomized controlled trial. ANZ journal of surgery, 80(3), pp.169-173. Available from https://eprints.qut.edu.au/34283/1/c34283.pdf
Williams, R., Rankin, N., Smith, T., Galler, D. and Seakins, P., 1996. Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa. Critical care medicine, 24(11), pp.1920-1929. Available from https://journals.lww.com/ccmjournal/Abstract/1996/11000/Relationship_between_the_humidity_and_temperature.25.asp
Xiao, J., Shiu, E.Y., Gao, H., Wong, J.Y., Fong, M.W., Ryu, S. and Cowling, B.J., 2020. Nonpharmaceutical measures for pandemic influenza in nonhealthcare settings—personal protective and environmental measures. Emerging infectious diseases, 26(5), p.967. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7181938/pdf/19-0994.pdf
Yan, J., Grantham, M., Pantelic, J., De Mesquita, P.J.B., Albert, B., Liu, F., Ehrman, S., Milton, D.K. and EMIT Consortium, 2018. Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community. Proceedings of the National Academy of Sciences, 115(5), pp.1081-1086. Available from https://www.pnas.org/content/115/5/1081.full
Zhu, J.H., Lee, S.J., Wang, D.Y. and Lee, H.P., 2014. Effects of long-duration wearing of N95 respirator and surgical facemask: a pilot study. J Lung Pulm Resp Res, 4, pp.97-100. Available from https://www.ratical.org/PandemicParallaxView/JLPRR-01-00021.pdf
Zwart, M.P., Hemerik, L., Cory, J.S., de Visser, J.A.G., Bianchi, F.J., Van Oers, M.M., Vlak, J.M., Hoekstra, R.F. and Van der Werf, W., 2009. An experimental test of the independent action hypothesis in virus–insect pathosystems. Proceedings of the Royal Society B: Biological Sciences, 276(1665), pp.2233-2242. Available from https://royalsocietypublishing.org/doi/10.1098/rspb.2009.0064