Face masks during the COVID-19 pandemic
During the COVID-19 pandemic, face masks or coverings, including N95, FFP2, surgical, and cloth masks, have been employed as public and personal health control measures against the spread of SARS-CoV-2, the virus that causes COVID-19.
In community and healthcare settings, the use of face masks is intended as source control to limit transmission of the virus and for personal protection to prevent infection. Properly worn masks both limit the respiratory droplets and aerosols spread by infected individuals and help protect healthy individuals from infection.
Reviews of various kinds of scientific studies have concluded that masking is effective in protecting the individual against COVID-19. Various case-control and population-based studies have also shown that increased levels of masking in a community reduces the spread of SARS-CoV-2, though there is a paucity of evidence from randomized controlled trials. Masks vary in how well they work. Fitted N95s outperform surgical masks, while cloth masks provide marginal protection.
During the public health emergency, governments widely recommended and mandated mask-wearing, and prominent national and intergovernmental health agencies and their leaders recommended the use of masks to reduce transmission, including the WHO, American, European, and Chinese Centers for Disease Control and Prevention.
Types of masks
Many federal governmental agencies recommended using face masks to avoid COVID-19 transmission. Masks with exhalation valves were not recommended because they expelled the wearer's breath outwards, and an infected wearer would transmit the virus through the valve. A second purpose of face masks is to protect each wearer from environments that can infect them, which can be achieved by many models of masks.Various types of masks each provide different levels of protection against COVID-19 transmission, ease of use, and comfort:
- cloth face masks
- surgical masks
- certified face-covering masks, considered respirators, with certifications such as N95 and N99, and FFP
- filtering respirators with certifications such as N95 and N99, and FFP
- other respirators, including elastomeric respirators, some of which may also be considered filtering masks
In 2020, there were shortages of facial masks, which have led to the use of uncertified masks, with worse performance.
Cloth masks
A cloth face mask is worn over the mouth and nose and made of common textiles such as cotton. Masks vary widely in effectiveness, depending on factors such as material, fit and seal, and the number of layers. They are usually less effective at filtering than surgical masks and offer much less protection. Unlike disposable masks, there are no required standards for cloth masks.One 2020 study found that a cloth mask was better than nothing, but not as good as a soft electret-filter surgical mask for protecting healthcare workers while simulating the treatment of an artificially infected patient. Research on commonly available fabrics used in cloth masks found that cloth masks can provide significant protection against the transmission of particles in the aerosol size range, with enhanced performance across the nanoscale and microscale when masks use both mechanical and electrostatic-based filtration, but that leakage due to improper fit can degrade performance. A review of available research published in January 2021 concludes that cloth masks are not considered adequate to protect healthcare practitioners in a clinical setting.
A 2013 study had volunteers wear masks they made themselves from cotton T-shirts, following the pattern of a standard tie behind the head surgical mask, and found the number of microscopic particles that leaked to the inside of the homemade masks was twice that of commercial masks. Wearing homemade masks also leaked a median average of three times as many microorganisms as commercial masks. But another 2020 study found that masks made of at least two layers of T-shirt fabric could be as protective against virus droplets as medical masks, and as breathable.
A 2020 peer-reviewed summary of published literature on the filtration properties of cloth and cloth masks recommends two to four layers of plain-weave cotton or flannel of at least 100 threads per inch. There is a trade-off in that increasing the number of layers increases the filtration of the material but decreases how easy it is for a person to breathe through the mask.
As of May 2020, there was no research on decontaminating and reusing cloth masks. The CDC recommends removing a mask by handling only the ear loops or ties, placing it directly in a washing machine, and immediately washing hands in soap and water for at least twenty seconds. Cold water is considered as effective as warm water for decontamination. The CDC also recommends washing hands before putting on the mask and again immediately after touching it.
There is no information on reusing an interlayer filter. Disposing of filters after a single use may be desirable. A narrative review of the literature on the filtration properties of cloth and other household materials did not find support for using a filter. A layer of cloth, if tolerated, was suggested instead, or a PM2.5 filter, as a third layer.
The United States Environmental Protection Agency Study published on 5 April 2021, showed extremely varied performance across cotton masks. The results of the EPA study found that "a three-layer knitted cotton mask blocked an average of 26.5 percent of particles in the chamber, while a washed, two-layer woven nylon mask with a filter insert and metal nose bridge blocked 79 percent of particles on average." Ultimately, the researchers found that fabric and fit are the two most vital factors when recommending masks to the public and further research is being conducted on variables such as facial hair and face shape on mask fit.
Surgical masks
A surgical mask is a loose-fitting, disposable mask that creates a physical barrier separating the mouth and nose of the wearer from potential contaminants in the immediate environment. If worn properly, a surgical mask is meant to help block large-particle droplets, splashes, sprays, or splatter that may contain viruses and bacteria, keeping them from reaching the wearer's mouth and nose. Surgical masks may also help reduce exposure of others to the wearer's saliva and respiratory secretions.Certified medical masks are made of non-woven material, and they are mostly multi-layer. Filters may be made of microfibers with an electrostatic charge; that is, the fibers are electrets. An electret filter increases the chances that smaller particles will veer and hit a fiber, rather than going straight through. While there is some development work on making electret filtering materials that can be washed and reused, current commercially produced electret filters are ruined by many forms of disinfection, including washing with soap and water or alcohol, which destroys the electric charge. During the COVID-19 pandemic, public health authorities issued guidelines on how to save, disinfect and reuse electret-filter masks without damaging the filtration efficiency. Standard disposable surgical masks are not designed to be washed. Surgical masks may be labeled as surgical, isolation, dental, or medical procedure masks. The material surgical masks are made from is much poorer at filtering very small particles than that of filtering respirators and the fit is much poorer. Surgical masks are made of a non-woven fabric created using a melt blowing process. Random control studies of respiratory infections like influenza find little difference in protection between surgical masks and respirators. However, the filtering performance of correctly worn N95/FFP2 type filtering respirators is clearly superior to surgical and to cloth masks and for influenza, work by the UK Health and Safety executive found that live virus penetrated all surgical masks tested but properly fitted respirators reduced the viral dose by a factor of at least a hundred.
Surgical masks made to different standards in different regions of the world have different ranges of particles which they filter. For example, the People's Republic of China regulates two types of such masks: single-use medical masks and surgical masks. The latter ones are required to filter bacteria-sized particles and some virus-sized particles, while the former ones are required to only filter bacteria-sized particles.
Modifications
The effectiveness of surgical masks in limiting particle transmission is a function of material and fit. Since the start of the pandemic, scientists have evaluated various modifications to ear loop surgical masks aimed at improving mask efficacy by reducing or eliminating gaps between the mask and face. The CDC evaluated and recommended two such modifications to ear loop masks to minimize the transmission of SARS-CoV-2. Under regular use, the CDC found that a surgical mask worn by a coughing individual blocked 41.3% of simulated cough aerosols from reaching a second individual six feet away. However, by applying a knot and tuck technique, 62.9% of particles were blocked. When the surgical mask was covered with a larger cloth mask, 82% of the particles were blocked. When both the source and recipient wore masks, 84% of the particles were blocked. The number increased to more than 95% when both parties either wore double masks or used the knot and tuck technique.Another type of modification was aimed to improve the comfort of the wearers. Early in the pandemic, healthcare workers were required to continue wearing surgical masks for 12 or more hours a day. This caused the ear loops of the masks to chafe the back of their ears. Ear savers, plastic straps, and hooks that go around wearer's heads, were invented to move the ear loops away from the wearer's ears. They could be made on demand by using a 3D printing process.
An improved version approaches the model efficacy of N95 respirators.