A comparison of the different types of face mask

In 2019, a new virus emerged from Wuhan in China. Coronavirus 2019 (COVID-19) has rapidly spread across the globe in a pandemic from which the world has yet to recover. Emergency control measures, including border closures, containment and diversion of health resources, have been implemented in different countries to varying degrees in recent years. The demand for clinical personal protective equipment (PPE) has grown exponentially as the number of coronavirus cases soared and introduced a new normal in the wider community.

Image Credit: bohemama/Shutterstock.com

Face masks are traditionally worn in East Asian countries during illness and cold/flu season. This method has started to be adopted by other countries to limit the infection rate in the fight against COVID-19. Individuals become contagious 2.5 days before symptoms appear, making masking an important preventative measure. To maintain the flow of PPE to clinicians, the public is using cloth masks, face shields and single-use face masks. Face masks were produced with vents, and East Asian markets produced KN95 and KF95 masks as alternatives to the US N95.

Different countries have their own medical mask certification system. These masks can be produced solely for the clinical market with generally superior filtration efficiency and various outer fabrics for functions such as splash resistance. These masks follow the standards that govern their country of origin. Due to the COVID-19 pandemic, the rules have been relaxed to tackle the shortage of PPE, allowing the use of masks meeting equivalent regulations in countries other than their place of manufacture.

Putting on the masks

The masks have been applied in the West on the basis of the precautionary principle, without tangible proof of the effectiveness of face masks. Literature reviews from the first quarter of 2020 were aware of the lack of scientific investigation covering the protection offered by face masks against COVID-19. This research was aimed at studies of face masks and similar viral outbreaks.

Assuming a similar result to a review in 2010 on face masks and flu outbreaks, there were enough potential benefits that encouraged face mask adoption – although the review did highlight a benefit for masks when worn only by symptomatic people. A small Australian study from 2009 demonstrated a statistically significant benefit to wearing face masks against the flu.

Following this, two further reviews in April and May 2020 were published in pre-print to examine the effectiveness of face masks against respiratory illnesses, including influenza. These reviews used previous studies that included randomized controlled trials. Both of these reviews concluded that there was no statistically significant benefit to wearing face masks against infection. A limitation of reviewing the scientific literature regarding other respiratory viruses is that COVID-19 is more infectious with greater consequences.

Studies are underway to investigate the prevention effectiveness of face masks against COVID-19 in particular. An experiment spraying COVID-19 in aerosol form concluded that while the virus can remain airborne for several hours, surgical masks could act as a barrier. A longitudinal study in Hong Kong examined the effect of non-medical precautions taken against COVID-19: social distancing and face masks. The conclusion showed a statistically significant benefit.

A study in late 2020 plotted regional public data in Germany to measure the impact of mask-wearing, as masks became mandatory at different times in different regions. The study concludes that face masks reduced the number of new infections by 45% after 20 days of mandatory use. The biggest reduction of more than 50% was seen in the 1960s, as face masks became standard PPE in nursing homes.

Effectiveness of consumer masks

The lockdowns have brought out the creativity of the public, with many people making their own washable cloth masks. A study from Stanford University found that cloth masks are only 10-35% effective in stopping particle-sized aerosol particles of COVID-19. Compared to surgical masks – it’s usually the single-use blue masks that are widely available – which were 95% effective in stopping these aerosol particles from passing through.

Image credit: View Apart/Shutterstock.com

Surgical masks are made of polypropylene and are shaped by high temperature fusion. This structural makeup is more effective at stopping particles than woven fabric. The blue or colored outer layer acts as a water repellent while the inner layer is absorbent. Stanford University found that these masks could remain effective after rinsing or even washing for 10 cycles, no longer requiring users to throw them away after just one use.


The market also boasts N95, KN95 and KF95 respirator masks. These can come in various sizes and shapes such as boat, cone and cup with adjustable straps and versions for children. Tighter than surgical masks, these specialised masks come with either internal or external nose clips to be pinched into shape. All of these masks are formed from overlapping polymer fibres allowing gaps within microns in size and may have a respirator attached to the outside layer.


The number 95 on the masks indicates that these masks should have a 95% filtration efficiency, typically against particles of 0.3µm in size, although this may vary depending on the brand. Although COVID-19 viral particles are postulated to be 0.1µm in size, they are transmitted through larger aerosol or droplet vehicles. The majority of these larger vehicular particles range from 4-8µm. Viral residue can linger in the air beyond the evaporation of the droplet; the size of these infectious particles ranges from 0.5µm-20µm.


N95 masks are approved by the National Institute for Occupational Safety and Health (NIOSH) using guidelines from the Centre for Disease Control (CDC) in the United States. These masks are made to ASTM F3502-21 standard and are also used in American and British hospitals. Masks approved for use in the EU receive a CE mark which will be displayed on the packaging.


KN95 masks are a Chinese alternative, following the Chinese standard GB2626:2006. These are advertised as having the same filtration efficiency as N95 masks but have been targeted by an overwhelming number of fakes across the online market space, which do not meet the required standard.


Several types of KN95 masks have received approval from NIOSH. KF95 masks are Korean masks that are marked with 95% filtration efficiency although they have not yet been approved by NIOSH. Both types of masks will bear a CE mark on the packaging if they have met the criteria for the EU in the Personal Protective Equipment Regulations (EU) 2016/425.


Medical and fabric masks: who wears what when?


References:


  • Greenhalgh T, Schmid M B, Czypionka T, Bassler D, Gruer L. Face masks for the public during the covid-19 crisis BMJ 2020; 369:m1435 doi:10.1136/bmj.m1435. Available at https://www.bmj.com/content/369/bmj.m1435
  • Bissett, J., 2020. [online] nhsprocurement.org.uk. Available on : .
  • US Food and Drug Administration. 2021. N95 respirators, surgical masks, face masks and protective face coverings. [online] Available on : .
  • Timo Mitze, Reinhold Kosfeld, Johannes Rode, Klaus Walde. Face masks drastically reduce COVID-19 cases in Germany, Proceedings of the National Academy of Sciences Dec 2020, 117(51)32293-32301; DOI: 10.1073/pnas.2015954117. Available at https://www.pnas.org/content/117/51/32293
  • Jayaweera, M., Perera, H., Gunawardana, B. and Manatunge, J. (2020). Transmission of the COVID-19 virus by droplets and aerosols: a critical examination of the unresolved dichotomy. Environmental research, 188, 109819. https://doi.org/10.1016/j.envres.2020.109819. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293495/

Further reading

Comments are closed.