With So Many Masks, Which One Should You Invest In?
By Ryan Mathura, B.S.—Health Science
Mr. Mathura is pursuing his Master of Public Health degree from Emory University in Atlanta, GA, USA. This summer, he is also working as a COVID-19 contact tracing intern for the Georgia Department of Public Health.
Mask-wearing has become a hot topic during the novel coronavirus pandemic, inspiring debate among scientists, politicians, and the media. After review of evidence, the World Health Organization (WHO) has recommended mask wearing for all healthcare workers (HCWs) taking care of COVID-19-positive patients. HCWs should wear high-filtration respirator-style masks during any aerosol generating procedure with COVID-19-positive patients. Outside of healthcare, the WHO recommends medical masks for anyone with symptoms or in close contact with suspected COVID-19-positive patients. The WHO also supports universal public masking, including the use of fabric non-medical masks, in areas with community transmission or large-scale outbreaks, such as South Africa and the United States.
While shortages persist, medical masks and respirators are reserved for front-line workers and high-risk populations. Many people have therefore resorted to making their own masks out of household materials with varying efficiencies. Now that the supply of masks has increased, people are not sure which ones to make or buy.
Figure 1. The four principles of filtration. This image was made available by Wikimedia for public use via Creative Commons license.
What are the important factors to consider when deciding which mask to wear?
Cloth masks, medical masks, and respirators are all types of fibrous masks. They are judged on their efficiency in filtering, or blocking the passage of particles, as well as their breathability. The factors that determine filtration efficiency and also affect breathability are:
Fiber diameter: The size of individual fibers
Porosity: The ratio of open space to closed space
Filter thickness: The distance that particles must cross
There are four principles of physics that contribute to filtration efficiency, as well. These are:
Interception
Fibers physically block particles as they come into contact
Useful for blocking large particles
Inertial impaction
Particles are too heavy to follow the airstream through the fibers
Useful for blocking large particles
Diffusion
Small particles are bombarded by other molecules and do not follow the airstream
Useful for blocking small particles
Electrostatic attraction
Charged fibers trap oppositely charged particles
Useful for blocking charged particles of any size
Homemade cloth masks and most medical masks rely on interception, inertial impaction, and diffusion to filter particles. According to a study by Davies et al (2013) on the efficacy of homemade masks made of different materials, the best efficacy and breathability comes from using two pillowcases, with only a 4% decrease in breathability while filtering up to 68% of 0.02-micron particles [1]. The WHO now recommends a three-layer fabric mask for community use during the coronavirus pandemic. These masks optimize filtration while maintaining breathability.
Fortunately, emerging data show that some household materials are very effective at filtration and are appropriate for those not working at the frontline. According to a recent article in the American Chemical Society ACS Nano journal, multi-layered cotton masks are the most effective [3]. This is consistent with the WHO guidelines to use a three-layered mask. However, gaps caused by obstructions such as facial hair or poor nosepiece fit significantly reduce the efficacy of such masks, so ensuring a good fit is essential. Mask wearers must take care not to touch their face when donning and doffing masks, as well.
Figure 2. The three-layer fabric mask. This video from the WHO provides details on the three-layer fabric mask, which provides a higher level of breathability and filter efficacy than one-layer cotton masks.
Particulate respirators are a special kind of mask recommended for use in some healthcare settings when working with COVID-19 patients. These masks not only use the principles of inertial impaction and diffusion, but they also take advantage of the principle of electrostatic attraction. Respirators are judged on their ability to filter 3-micron particles because particles of this size are too small to be reliably trapped by interception or inertial impaction but too large to be blocked by diffusion. Respirators must meet stringent testing regulations. N95 masks are tested according to US regulations, while KN95 are tested according to Chinese standards and FFP2 masks meet European criteria. All three of these respirators filter approximately 94-95% of 3-micron particles.
Respirators are the gold standard for personal protection against infection from airborne disease. So why are many countries encouraging that the public wear cloth masks instead of respirators?
The shortage of respirators and medical masks has led to prioritization for frontline workers in the coronavirus pandemic. Frontline workers are those who perform essential services for a community, including HCWs, janitors, police, and teachers. They are at a higher risk of not only being exposed to the virus but also being exposed to higher concentrations of the virus making it increasingly likely to contract the disease [2].
Finally, while they can be helpful to reduce risk, masks alone cannot guarantee against the spread of COVID-19. Masks must be used in combination with good hand hygiene and appropriate physical distancing. You can read more about these preventative measures in our Scientific Resource Hub article here.
Key Messages on Mask Wearing
Three-layer homemade masks made of efficient and comfortable material should be adequate enough for most people when used in combination with hand hygiene and other infection prevention practices. Many clothing companies are now selling cloth masks, making them available to people who lack the skills, materials, and/or time to make them themselves. You can also learn how to make your own three-layer mask by checking out this video from the WHO. If you are a healthcare professional, in contact with COVID-19 patients, or interact with high-risk individuals, then a respirator or medical mask may be more appropriate for you.
Either way, keep your mask on and your community safe while COVID-19 is still rampant!
Mr. Mathura has no financial involvement or interest in the Bio Africa Marketplace or products mentioned therein or elsewhere within the BioAfrica Innovation Hub websites. His role in the Scientific Resource Hub does not constitute endorsement or recommendation of specific products or suppliers mentioned within the Bio Africa Innovation Hub websites.
References
Publicly available websites and news articles are linked in the text. Full references for peer-reviewed articles or other sites not publicly accessible are available below.
1. Davies, A., et al., Testing the efficacy of homemade masks: would they protect in an influenza pandemic? Disaster Med Public Health Prep, 2013. 7(4): p. 413-8.
2. Sim, M.R., The COVID-19 pandemic: major risks to healthcare and other workers on the front line. Occup Environ Med, 2020. 77(5): p. 281-282.
3. Konda, A., et al., Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano, 2020. 14(5): p. 6339-6347.