Plenty to read here about masks.
N95 masks and re-breathing respired (exhaled) air:
Evaluation of rebreathed air in human nasal cavity with N95 respirator: a CFD study
https://www.oatext.com/pdf/TEC-1-106.pdf
Cloth masks: Dangerous to your health?
Cloth masks: Dangerous to your health?
Masks may actually increase your coronavirus risk if worn improperly, surgeon general warns
Masks may actually increase your coronavirus risk if worn improperly, surgeon general warns - CNN
Face masks cannot stop healthy people getting Covid-19, says WHO
Face masks cannot stop healthy people getting Covid-19, says WHO
No good choices: A mask may block out some pollution but have other ill health effects
A mask may also cause respiratory distress and become a hotbed for microbes to thrive.
No good choices: A mask may block out some pollution but have other ill health effects
Driver in crash may have passed out from wearing N95 mask too long.
Driver in crash may have passed out from wearing N95 mask too long: Police
“‘The average healthy person does not need to have a mask, and they shouldn’t be wearing masks,’ Dr. Perencevich said. ‘There’s no evidence that wearing masks on healthy people will protect them. They wear them incorrectly, and they can increase the risk of infection because they’re touching their face more often.’”
Masks Prevent You From Infecting Others With Coronavirus, But May Not Protect You From Being Infected
Cloth masks: Dangerous to your health?
“Respiratory infection is much higher among healthcare workers wearing cloth masks compared to medical masks, research shows. Cloth masks should not be used by workers in any healthcare setting, authors of the new study say.”
Cloth masks: Dangerous to your health?
A cluster randomised trial of cloth masks compared with medical masks in healthcare workers
During Hemodialysis:
"Seventy percent of the patients showed a reduction in partial pressure of oxygen (PaO2), and 19% developed various degrees of hypoxemia [low blood oxygen]. Wearing an N95 mask significantly reduced the PaO2 level and increased respiratory adverse effects…”
The physiological impact of wearing an N95 mask during hemodialysis as a precaution against SARS in patients with end-stage renal disease - PubMed
Report on surgical mask induced deoxygenation during major surgery.
“Our study revealed a decrease in the oxygen saturation of arterial pulsations (SpO2) and a slight increase in pulse rates compared to preoperative values in all surgeon groups.”
Preliminary report on surgical mask induced deoxygenation during major surgery - PubMed
A cluster randomised trial of cloth masks compared with medical masks in healthcare workers.
“The rates of all infection outcomes were highest in the cloth mask arm, with the rate of ILI statistically significantly higher in the cloth mask arm…”
“An analysis by mask use showed ILI (RR=6.64, 95% CI 1.45 to 28.65) and laboratory-confirmed virus (RR=1.72, 95% CI 1.01 to 2.94) 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%.”
“Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection.”
A cluster randomised trial of cloth masks compared with medical masks in healthcare workers
Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks?
“Viral particles, or virions, are one of the smallest known bioaerosol agents, with a particle diameter ranging from 20 to 300nm.”
Regarding the size of virions and penetration of N95 masks:
“Similar results were reported by Martin and Moyer, who found that the maximum penetration of particles through the fiber-charged N95 respirators occurred in the 50- to 100-nm size range. Thus it should be emphasized that the certified N95 respirators will protect their wearers properly against the particles of 300 nm and larger, but their performance may be be- low the threshold for aerosol particles of the nanosize range.”
For one of the surgical masks tested, “the penetration increases with increasing particle size to 84.5% for particles of 80 nm in diameter…”
“The penetration data presented in this paper were obtained using manikin-based tests. Thus, the respirators and surgical masks were sealed to the manikin’s face. Such procedure eliminated the leakages, which can occur when a subject wears the personal respiratory protection devices. In real life, the leaks may lead to considerably increased particles penetration. ...without proper fit testing,
the wearer of a respirator cannot achieve the desired protection level.”
“The results indicate that N95-certified respirators may not necessarily provide a proper protection against virus, which is considerably smaller than the accepted most penetrating particle size of 300 nm used in the certification tests.”
“The N95 filtering face piece respirators may not provide the expected protection level against small virions. Some surgical masks may let a significant fraction of airborne viruses penetrate through their filters, providing very low protection against aerosolized infectious agents in the size range of 10 to 80 nm.”
https://www.ajicjournal.org/article/S0196-6553(05)00911-9/fulltext
https://moscow.sci-hub.tw/1624/d77d741064f86207488d41afba2c8609/10.1016@j.ajic.2005.08.018.pdf
Headaches Associated With Personal Protective Equipment - A Cross-Sectional Study Among Frontline Healthcare Workers During COVID-19.
81.0% of respondents developed de novo PPE-associated headaches.
https://pubmed.ncbi.nlm.nih.gov/32232837/
60% of inspired air is respired air when wearing a properly fitted N95 mask.
OSHA Respiratory Protection Standard states that any atmosphere below 19.5% oxygen is dangerous for human health.
If 60% of air is re-breathed/previously exhaled air, consisting of 16% oxygen, and 40% of the air breathed is 21% oxygen, the overall percentage of oxygen in 100% of the air being breathed in while wearing a mask, is 18%. Well below the 19.5% OSHA standard.
https://www.oatext.com/pdf/TEC-1-106.pdf
Use of Surgical Face Masks to Reduce the Incidence of the Common Cold Among Health Care Workers in Japan: A Randomized Controlled Trial. (Didn’t work.)
https://pubmed.ncbi.nlm.nih.gov/19216002/
An article published April 6th, 2020, states:
“Limited, indirect evidence from lab studies suggests that homemade fabric masks may capture large respiratory droplets, but there is no evidence they impede the transmission of aerosols implicated in the spread of COVID-19, according to a paper published yesterday by the National Academy of Sciences, Engineering, and Medicine.
In the paper, the National Academies' Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats said that, because no studies have been done on the effectiveness of cloth masks in preventing transmission of coronavirus to others, it is impossible to assess their benefits, if any.”
https://www.cidrap.umn.edu/news-per...t-back-cloth-masks-limit-covid-19-experts-say
“At present, there is no direct evidence (from studies on COVID- 19 and in healthy people in the community) on the effectiveness of universal masking of healthy people in the community to prevent infection with respiratory viruses, including COVID-19.”
https://apps.who.int/iris/rest/bitstreams/1279750/retrieve
Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure:
“our results suggest that cloth masks are only marginally beneficial in protecting individuals from particles<2.5 μm.”
https://pubmed.ncbi.nlm.nih.gov/27531371/
“...common fabric materials may provide marginal protection against nanoparticles including those in the size ranges of virus-containing particles in exhaled breath.”
https://www.ncbi.nlm.nih.gov/pubmed/20584862
“None of the studies established a conclusive relationship between mask/respirator use and protection against influenza infection.”
https://www.ncbi.nlm.nih.gov/pubmed/22188875
“Wearing N95 masks results in hypooxygenemia and hypercapnia which reduce working efficiency and the ability to make correct decision.
Medical staff are at increased risk of getting 'Severe acute respiratory syndrome'(SARS), and wearing N95 masks is highly recommended by experts worldwide. However, dizziness, headache, and short of breath are commonly experienced by the medical staff wearing N95 masks.”
https://clinicaltrials.gov/ct2/show/NCT00173017
Reusing masks may increase your risk of coronavirus infection, expert says:
https://www.news-medical.net/news/2...isk-of-coronavirus-infection-expert-says.aspx
“Masks-for-all for COVID-19 not based on sound data.”
Commentary from Dr. Brosseau, a national expert on respiratory protection and infectious diseases and professor (retired), University of Illinois at Chicago, and Dr. Sietsema, also an expert on respiratory protection and an assistant professor at the University of Illinois at Chicago.
https://www.cidrap.umn.edu/news-per...ntary-masks-all-covid-19-not-based-sound-data
N95 masks may be effective but not other masks:
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31142-9/fulltext#
N95-masked health-care workers (HCW) were significantly more likely to experience headaches. Face mask use in health care workers has not been demonstrated to provide benefit in terms of cold symptoms or getting colds (colds are caused by coronaviruses).
https://www.ncbi.nlm.nih.gov/pubmed/19216002
Face masks to prevent transmission of influenza virus: a systematic review.
There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission. There are fewer data to support the use of masks or respirators to prevent becoming infected.
https://www.cambridge.org/core/jour...matic-review/64D368496EBDE0AFCC6639CCC9D8BC05
The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence.
“There were 17 eligible studies… None of the studies established a conclusive relationship between mask/respirator use and protection against influenza infection.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5779801/#idm140166105578400title
“We identified six clinical studies … . 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.”
“Initial guidelines on preventing acute respiratory infection relied on surrogate exposure data and data extrapolated from the protection of health care workers against tuberculosis because clinical evidence did not exist at that time.”
Effectiveness of N95 respirators versus surgical masks in protecting health care workers from acute respiratory infection: a systematic review and meta-analysis.
https://www.cmaj.ca/content/188/8/567
“Compared to masks, N95 respirators conferred superior protection against [clinical respiratory illness] (RR = 0.47; 95% CI: 0.36–0.62) and laboratory-confirmed bacterial (RR = 0.46; 95% CI: 0.34–0.62), but not viral infections or [influenza-like illness].”
“Self-reported assessment of clinical outcomes was prone to bias. Evidence of a protective effect of masks or respirators against verified respiratory infection (VRI) was not statistically significant.”
Effectiveness of Masks and Respirators Against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis.
https://academic.oup.com/cid/article/65/11/1934/4068747
“In this pragmatic, cluster randomized clinical trial involving 2862 health care personnel, there was no significant difference in the incidence of laboratory-confirmed influenza among health care personnel with the use of N95 respirators (8.2%) vs medical masks (7.2%).”
N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial.
https://jamanetwork.com/journals/jama/fullarticle/2749214
“N95 respirators should not be recommended for general public and nonhigh‐risk medical staff those are not in close contact with influenza patients or suspected patients.”
“The use of N95 respirators compared with surgical masks is not associated with a lower risk of laboratory-confirmed influenza.”
“There were no statistically significant differences in preventing laboratory-confirmed influenza, laboratory-confirmed respiratory viral infections, laboratory-confirmed respiratory infection, and influenza-like illness using N95 respirators and surgical masks. Meta-analysis indicated a protective effect of N95 respirators against laboratory-confirmed bacterial colonization (RR = 0.58, 95% CI 0.43-0.78).”