COVID-19 Section 5: Transmission and face masks

Introduction: face masks: a barrier to COVID-19

This chapter provides an insight on the use of face masks during a pandemic and how face masks can help curb the spread of various air or aerosol-borne infectious diseases.

Face masks, although a personal protective equipment (PPE) by function, have been shown to be one of the effective measures to help in stopping the spread of the pandemic when the majority of the population adopts it early on. This chapter will discuss the various face masks available to the general public and their efficacy along with the key issues and concerns regarding face masks.

COVID-19 has disabled numerous operations around the world affecting the lives of many people. The transmission of the virus needs to be extensively studied to reduce the number of infections and control the infection rate of the virus.

Development of effective control measures against aerosol or airborne transmission of infections with various outbreaks like Severe Acute Respiratory Syndrome (SARS), human avian influenza A (H5N1), pandemic influenza A (H1N1/2009), and ongoing COVID-19 have become important. [1]

Airborne transmissions can transmit small particulates through the air over time and distance. Airborne transmissions are usually distinct from transmission by respiratory droplets. Respiratory droplets are droplet particles greater than 5-10 μm in diameter whereas droplets less than 5 μm are referred to as droplet nuclei. Transmission of infectious agents may occur via short-range, large-droplet aerosols and long-range, smaller, airborne droplet nuclei as shown in Figure 1. [2]

Different transmission routes of airborne and aerosol infections
Figure 1. Illustration of different transmission routes of airborne and aerosol infections (Credit: Elsevier COVID-19 resource centre.

Wearing face masks can prevent transmission and breathe in infectious droplets to a certain degree, while hand hygiene and social distancing can together make a significant contribution to the prevention of COVID-19. [2]

Purpose of face masks

Face masks serve several purposes; they help prevent an infected person from spreading the virus, as well as help blocking an uninfected individual from exposure to the virus. Face masks can reduce the possibility of people touching their mouth and nose with contaminated hands or other objects.

Figure 2 shows the probability of a person being affected by aerosol or airborne virus in different scenarios. The probability greatly reduces when both individuals wear face masks. One common misunderstanding is to assume face masks are mainly used to protect the wearers against contacting the virus. Depending on the application and type of masks, most face masks available in the market are designed to protect others against the wearer. They do this by capturing the aerosols and droplets exhaled by the infected person. By doing this at the source, they prevent the droplets evaporating and so can reduce the likelihood that there are aerosols in the environment as well as reducing larger droplets.  Although source control is the main purpose of the mask, they do also provide some protection to the wearer from inhaling aerosols.  

Transmission risk related to wearing masks
Figure 2. Transmission risk related to wearing masks 

Adopting a face mask

Adopting face masks at an early stage in the outbreak can significantly reduce the number of infections sooner. Masking has been one of the main barriers and has become mandatory for the public for the duration of the pandemic in most of the Eastern countries at the onset of the COVID-19 pandemic. [4] They have been slowly adopted in Western countries over the past eight months.

Face masks in public

US Centre for Disease Control and Prevention (CDC) also recommends the use of face masks in public settings when social distancing of six feet is not possible. CDC agrees that masks can help stop the spread of COVID-19 to others. [10]

Relative risk (RR) reductions for infections

Systematic reviews of the use of face masks also suggest relative risk (RR) reductions for infections ranging from 60-80%, depending on the type of masks used. Despite the high range, possible RR reduction must be considered. In Norway, for example, it was estimated that 200 000 people would need to wear face masks to prevent one new infection per week. They assumed a 40% RR reduction with the use of surgical masks [5].

Face mask tests

Different standardised tests are conducted to ensure performing properties are validated like:

  • Bacterial or Viral Filtration Efficiency (BFE/VFE)
  • differential pressure
  • flammability test
  • particle filtration efficiency
  • synthetic blood fluid penetration resistance.

Appendix 1 shows the details and the different levels of surgical face masks.

Different types of masks and their uses


There are different types of face masks available in the market. These include a basic washable cloth face mask, surgical face mask, copper mask, N95 respirator, etc.  Each has its own specific applications and offers a different degree of protection against COVID-19 transmission. Various tests have been performed for different types of face masks based on their use.

Cotton masks

Few researchers point out that cloth masks made of tightly woven with 100% cotton material are relatively better than other cloth masks.

A reason for this could be that the natural structure of cotton tends to have a more three-dimensional structure than synthetic fibers which eventually creates more blocks when the particles enter. Although masks with multiple layers are deemed to be more effective in blocking small particles, fabric, breathability and fit should also be kept in mind while choosing or making a mask [17].

Cloth masks

Cloth masks

Figure 3. Cloth masks

In circumstances where there is a limited supply of surgical masks, cloth masks can be an alternative for use in public. Cloth masks are defined as masks made of cloth or any other fabric such as cotton, gauze, silk, or muslin as shown in Figure 3.

The filtration effectiveness of cloth masks is lower than that of surgical masks or respirators, but can provide some protection if it is designed to fit around the face and made water-resistant [6,7]. Some cloth masks allow a filtering layer that can enhance the protection against transmission.

Since there is no specific technical standard or specifications to most of these cloth masks, they can only be treated as a contingency in shortage of a better mask and should not be viewed as an alternative to a better mask due to their style and colourful designs.

Few researchers point out that cloth masks made of tightly woven with 100% cotton material are relatively better than other cloth masks. A reason for this could be that the natural structure of cotton tends to have a more three-dimensional structure than synthetic fibers which eventually creates more blocks when the particles enter. Although masks with multiple layers are deemed to be more effective in blocking small particles, fabric, breathability and fit should also be kept in mind while choosing or making a mask [17].

"Hybrid" mask

In one of the researches for cloth masks, UK researchers show that “hybrid” masks combining two layers of 600-thread-count cotton with materials like silk, chiffon, or flannel had a considerable effect in filtering small particles (about 80 percent) and large particles (more than 90 percent).

Findings showed that combination of cotton and chiffon offered the most protection followed by cotton and flannel, cotton and silk, and four layers of natural silk. Recommendations from the World Health Organisation (WHO) also state that fabric masks could have three layers: an inner layer which absorbs, a middle layer which filters, and an outer layer made from a non-absorbent material like polyester. [18]

Copper masks

Copper masks are masks infused with a copper metal mesh layer; copper oxide is known to display antiviral properties.

Research shows that copper oxide impregnated face masks may filter above 99.85% of aerosolized viruses when exposed to the H1N1 virus and avian influenza virus (H9N2) under simulated breathing conditions [9].

Another important finding from the research was that no infectious viral titers were recovered from the copper oxide masks within 30 minutes.

A cloth mask embedded with a copper mesh filter can significantly increase its efficacy and can be a viable alternative to a better mask unless being exposed to an environment that requires surgical masks [9].

Copper oxide

Impregnation of copper oxide into protective face masks enables them with potent anti-influenza biocidal properties without making any change to their physical barrier properties. This will assist in significantly reducing the risk of hand and environmental contamination and hence subsequent infection due to improper handling and disposal of the masks.

Several tests carried out show that the amount of copper eluted to air from test mask in a time period of 5 hours under simulated breathing conditions was 0.467±0.47 pg, which is far below the respiratory copper permissible exposure limit (PEL) set by USA Occupational Safety and Health Administration (OSHA) [9]. The outer layers of the masks which contain copper oxide particles also did not cause any skin sensitisation or skin irritation.

Properties of copper masks

Mass distribution of copper masks was done in Hong Kong around the month of May. CuMask+™, developed by the Hong Kong Research Institute of Textiles and Apparel (HKIRTA) consists of six layers with two layers specially made with small quantities of copper as shown in Figure 6.

This is capable of deactivating bacteria, common viruses, and other harmful substances. CuMask+™ complies with the American Society for Testing and Materials (ASTM) standards for particle filtration efficiency, bacterial filtration efficiency, resistance to penetration by synthetic blood, flammability, and pressure resistance [9].

Surgical masks

A surgical mask, also known as a medical face mask, is used by health professionals during health care procedures. These masks are designed to prevent infections in patients and personnel treating them by catching bacteria shed in liquid droplets and aerosols from the wearer's mouth and nose. An FDA-approved surgical mask is made from thin, disposable material as shown in Figure 4. It is important to note that surgical style masks sold in supermarkets and other shops are similar in appearance but do not necessarily meet the same standards as masks designed for clinical use.

Figure 4. Surgical mask

Figure 4. Surgical mask

Surgical mask properties

Surgical masks are made of nonwoven fabric created using a melt blowing process. These masks are disposable, loose-fitting masks. A metal strip at the top of the mask can be formed around the nose of the user. [8] These are designed for single use only and should be disposed of after use. These masks must be removed and replaced with another one when they become moist.

Silicone masks

A relatively new finding, silicone masks, were developed by a research team at Massachusetts Institute of Technology (MIT) and Brigham and Women’s Hospital in Boston.

These masks are comparable to the performance of N95 masks and can also be sterilised and reused extensively.

They can be autoclaved and cleaned using dry or steam sterilisation and can be disinfected using alcohol and wipes. Although the designed mask fits criteria from the National Institute for Occupational Safety and Health (NIOSH), it is still under the process of finding a scalable solution [11].

Face shields

A face shield, an item of personal protective equipment, protects the wearer’s entire face from hazards, chemical splashes, or potentially infectious materials.

These are excellent at preventing droplets from coming into contact with the mouth, nose, and eyes but there are still high chances of inhaling droplets in the environment through the open areas around the plastic visor.

Face shields work best to protect the wearer from an infected person when used with a mask, as they provide no protection against aerosols [15].

N95 respirators

N95 respirators are respiratory protective devices that are engineered to achieve a very close facial fit and efficient filtration of airborne particles as shown in Figure 5.

N95 respirators are made of a material that filters most of the particles from the air when it passes through the face mask – as long as the respirator is correctly fitted. Most air being taken in passes through the face mask and is thus filtered, removing most or all virus particles.


N95 respirator
Figure 5. N95 respirator

Reuse of respirators

Ideally, respirators should be disposed of after each use, however, under certain conditions, they can be reused by the same person. These respirators should not be used when it is crushed, torn or creased, soiled or splashed with potentially infectious secretions or wet – no matter which liquid it has been wet with, or when it becomes difficult to breathe while wearing it.

Respirators may be reused, only if they are in short supply.

They can be reused by the same person, not shared among different people. If properly cared for, respirators can last one week or more. It must not be cleaned. They should be stored in a clean and dry location when not in use. They may be wrapped with a dry cloth or tissue. These should not be wrapped in plastic as this tends to retain moisture and reduce the face mask’s efficacy. Exposing used N95 masks to the right spectrum of UVC can help sanitise the mask in between use. [6, 7].

Face mask: how to wear

While wearing a face mask is essential, wearing them with proper precautions is also important:

  • Hands should be properly cleaned with soap and water or hand sanitiser before and after the process of removing the mask
  • Mask should be checked for any tears or holes before being used
  • The coloured side of the mask is usually in the front and away from the face while the white side faces towards the face.
  • Hands should be thoroughly cleaned before and after the process of removing the mask. Touching the front face of the mask should be avoided. Mask should be properly discarded in the trash.
  • The mask should fit snugly, without wide gaps at the sides or under the eyes. Masks that incorporate a bendable wire over the nose often fit better.

Key issues and concerns

People are advised to cover their nose and mouth while roaming around in public, as donning of face masks has proven to be important to help curb COVID-19. Other barriers like social distancing, personal hygiene can also help in creating a combined effective method to reduce the spread and chances of getting infected as can be shown in Figure 6. [11]

Figure 6. Swiss cheese model showing infection prevention


Figure 6. The Swiss cheese model showing various layers to prevent infectious diseases and control transmission risks

Correct methods on how to use masks and strict control by the governments not only on wearing masks but also on how they should be worn and handled can further reduce the spread of COVID-19. The Public must be trained about the correct way of putting on, wearing, removing, and disposing of face masks for face masks to be effective [12].

Although the SARS-COV-2 virus is very small it is contained in respiratory fluids which means that particles are larger than the virus alone. Particles in the submicron region (d p between 0.25 and 1.0 μm) and super micron region (d p > 2.5 μm), can be effectively filtered out from the inhaled air by either surgical masks or N95 masks. A recent COVID-19 dynamic modelling study also suggested that broad adoption of even relatively ineffective non-medical grade “social” masks may meaningfully reduce the community transmission and decrease peak hospitalizations and deaths during the current COVID-19 pandemic [13].

Homemade face masks

A study conducted on the effectiveness of homemade masks as an alternative to commercial masks concluded that surgical masks are more effective in preventing microorganisms than homemade masks.

Nevertheless, in short of supply scenarios, homemade cloth masks are better than no protection and 100% cotton is the best material to use while making them. The use of double-layer cotton masks reduces the emission of larger particles [14,16].

Face masks: shedding fibres

While utilising cloth masks, care must be taken while removing and cleaning the masks as cloth masks can be prone to shedding fibres and in turn lodge deposited micro-organisms [16]. Few tips for cloth masks are shown in Figure 7.

Figure 7: Good practices while using facemasks

Figure 7: Good practices while using facemasks [2]

Section 5 References

  1. Tang, J. W., Noakes, C. J., Nielsen, P. V., Eames, I., Nicolle, A., Li, Y., & Settles, G. S. (2011). Observing and quantifying airflows in the infection control of aerosol-and airborne-transmitted diseases: an overview of approaches. Journal of Hospital Infection, 77(3), 213-222.
  2. WHO – Use of facemasks 
  3. Wei, J., & Li, Y. (2016). Airborne spread of infectious agents in the indoor environment. American journal of infection control, 44(9), S102-S108.
  4. Kai, D., Goldstein, G. P., Morgunov, A., Nangalia, V., & Rotkirch, A. (2020). Universal masking is urgent in the COVID-19 pandemic: Seir and agent-based models, empirical validation, policy recommendations. arXiv preprint arXiv:2004.13553
  5. Schünemann, H. J., Akl, E. A., Chou, R., Chu, D. K., Loeb, M., Lotfi, T., ... & Mertz, D. (2020). Use of facemasks during the COVID-19 pandemic. The Lancet Respiratory Medicine, 8(10), 954-955
  6. Godoy, L. R. G., Jones, A. E., Anderson, T. N., Fisher, C. L., Seeley, K. M., Beeson, E. A., ... & Sullivan, P. D. (2020). Facial protection for healthcare workers during pandemics: a scoping review. BMJ global health, 5(5), e002553.
  7. Chughtai, A. A., Seale, H., & Macintyre, C. R. (2020). Effectiveness of cloth masks for protection against severe acute respiratory syndrome coronavirus 2. Emerging infectious diseases, 26(10).
  8. "Transmission-Based Precautions". U.S. Centers for Disease Control and Prevention. 2016-01-07. Retrieved 2020-03-31.
  10. Guidance on the use of masks to control influenza transmission.
  11. Engineers design a reusable alternative to N95 face mask.
  12. Jefferson, T., Foxlee, R., Del Mar, C., Dooley, L., Ferroni, E., Hewak, B., ... & Rivetti, A. (2008). Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic review. Bmj, 336(7635), 77-80.
  13. Cumbo, E., & Scardina, G. A. (2020). Management and use of filter masks in the “none-medical” population during the COVID-19 period. Safety Science, 104997
  14. Davies, A., Thompson, K. A., Giri, K., Kafatos, G., Walker, J., & Bennett, A. (2013). Testing the efficacy of homemade masks: would they protect in an influenza pandemic?. Disaster medicine and public health preparedness, 7(4), 413-418.
  15. Why plastic face shields aren’t a safe alternative to cloth masks.
  16. Asadi, S., Cappa, C. D., Barreda, S., Wexler, A. S., Bouvier, N. M., & Ristenpart, W. D. (2020). Efficacy of masks and face coverings in controlling outward aerosol particle emission from expiratory activities. Scientific Reports, 10(1), 1-13.
  17. A user’s guide to masks: What’s best at protecting others and yourself.
  18. Mantzari, E., Rubin, G. J., & Marteau, T. M. (2020). Is risk compensation threatening public health in the COVID-19 pandemic?. BMJ, 370.
  19. Coronavirus is not canceled: Wear your mask.

Section 5. Appendix: Medical face masks tests and requirements

Figure 8

Figure 8.

COVID-19 Task Force


Vincent Ho, Albany Tam, Rishita Boddu


COVID-19 Task Force

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