Do Masks Increase Risk of Transmission?

27 August 2020. Updated 29 August 2020.

The use of face coverings by the general public to help stop the spread of COVID-19 has become the most visible sign of the coronavirus pandemic, constantly reminding us that things are not normal. The idea behind the use of face coverings is that because a large number of COVID-19 sufferers (the majority?) have mild to no symptoms, wearing a face covering will prevent these individuals from inadvertently infecting others.

Current evidence is that COVID-19 is transmitted via two main routes: respiratory droplets and surface contact. Face coverings are assumed to be effective at capturing respiratory droplets, which is the rationale for their use. But what about their impact on transmission through surface contact?

The aim of face coverings is to prevent an asymptomatic individual from infecting others. For such an individual, their face covering would become saturated with respiratory droplets containing coronavirus and in fact, the more effective the face covering, the more virus it will have captured. So if an infectious individual touched their face covering, they would potentially be contaminating their fingers with coronavirus…which they could then transfer to the next thing they touched – like a door-handle, handrail or table.

Although such an individual could have still contaminated their hands and the environment whilst not wearing a face covering, the fact that the face covering has captured viral particles means that it provides a much more concentrated source of the virus. Additionally, putting a cloth covering on your face will almost certainly increase the probability that someone would touch their face to adjust or fiddle with it, especially if it is not well fitted. This further increasing the likelihood that an infectious individual would actually touch the contaminated cloth material.

Depending on the material that the individual contaminated, the coronavirus could remain viable and infectious in the environment for a long-time, especially if the transferred material is more concentrated.

In such a situation, the face covering could increase the possibility of transmission by providing a ready reservoir of virus for surface contamination and encouraging the individual to touch this reservoir!

Clearly, this possibility is recognised as an issue because the UK government’s guidance on the use of face-covering has the following points on using them properly:

  • Wash your hands thoroughly with soap and water for 20 seconds or use hand sanitiser before putting a face covering on
  • Avoid touching the part of the face covering in contact with your mouth and nose, as it could be contaminated with the virus
  • Change the face covering if it becomes damp or if you’ve touched it
  • Avoid taking it off and putting it back on a lot in quick succession (for example, when leaving and entering shops on a high street)
  • Wash your hands thoroughly with soap and water for 20 seconds or use hand sanitiser before removing
  • Only handle the straps, ties or clips

The trouble is, these points are nice-to-haves and bear little resemblance to what actually happens in real life.

If you were to follow this guidance, then it would almost certainly help in reducing infections, but not necessarily because of the face covering. In fact, if you remove the face covering from this list of actions you get:

  • Wash your hands thoroughly with soap and water for 20 seconds or use hand sanitiser before putting a face covering on
  • Avoid touching the part of the face covering in contact with your mouth and nose, as it could be contaminated with the virus
  • Change the face covering if it becomes damp or if you’ve touched it
  • Avoid taking it off and putting it back on a lot in quick succession (for example, when leaving and entering shops on a high street)
  • Wash your hands thoroughly with soap and water for 20 seconds or use hand sanitiser before removing
  • Only handle the straps, ties or clips

In other words, wash your hands frequently and don’t touch your face. If anything, the face covering appears to actually introduce an additional hazard (you have to replace it if you touch it) rather than provide any additional protection.

This list also highlights the major issue with the assumed effectiveness of face coverings, namely that these assessments have always been done in the context of other infection control measures and so the contribution, if any, of the face covering to reducing infection is impossible to understand.

In practice, how many people do any of the things on the Government’s ‘how to’ list, let alone all of them? Just walk around your local town or supermarket and observe the way people actually use face coverings and you’ll see how far the real world is from this ideal situation.

Using a face covering also has the potential to alter people’s behaviour, especially if they mistakenly believe that its purpose is to protect them from catching COVID-19 instead of transmitting it. For example, people may be less inclined to wash their hands or observe social distancing rules because they believe they are “safe”. This could further exacerbate the likelihood of surface transmission from an infected individual. The evidence for this is equivocal, with some studies indicating some people change their behaviour while others don’t, but it remains a realistic possibility (see this paper).

So overall it is very likely that in the real-world face coverings will lead to increased surface transmission of SARS-CoV-2. They provide a concentrated source of virus, they encourage face touching and could even reduce the use of effective countermeasures like hand washing. Whether face masks cause more harm than they prevent comes down to the risk of infection through the respiratory droplet route via the risk due to surface infection. Exploring this is entirely feasible with appropriately designed studies. The fact that no-one seems intent on really getting to the bottom of the actual usefulness of face covering smacks of the old adage “never ask a question you don’t want to know the answer to”.

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