What is the importance of masks?

Masks
By Prof. Erin Bromage
Translation by Dr Anastasia Drohan
June 3, 2020
Author: Prof. Erin Bromage, Dartmouth, Umass Univ.
Translation: Dr. Anastasia Drohan, Dermatologist

Masks should not be a political issue. They are a public health issue. But they have created confusion for several reasons. I hope to explain it simply here and demonstrate the importance in reducing SARS-CoV2 infections in our community.

When we breathe, talk, shout, sing, cough, or sneeze we release respiratory droplets. Little balls of mucus that shoot out of our mouths and noses into the air around us. Those little balls of mucus can pack a whole bunch of fun stuff – for example, bacteria and viruses. By far, bacteria are the easiest to see. For example, my 10-year-old son just finished an independent science project for school where he was trying to determine how many bacteria are in a cough. The answer….there are a lot of bacteria in a cough, even in healthy people!

Figure 1. Nutrient agar plate containing a single cough. Each spot on the plate is a colony of bacteria that grew over a 24-hour period.

Viruses are a little harder to measure. You have to catch respiratory droplets and put them in a tissue culture dish containing cells that allow the virus to grow. The presence of the virus in respiratory droplets from infected people has been demonstrated by many laboratories around the world (not by a 10-year-old in my kitchen).

Image 2: Respiratory droplet with virus.

Image 3: Respiratory droplets with social distancing of 2 meters (6 feet)

The size of the larger respiratory droplets allows for

The more virus is packed inside them. In contrast, each nucleus of small droplets may only contain a few viral particles. When we inhale small droplets, they can travel farther into the lung's airways than larger droplets, and then find a home in receptive lung tissues, more easily initiating an infection.

Face to Face Conversations:

Face-to-face conversations are one of the riskiest things you can do when there is a respiratory illness being transmitted in your community. It is even more worrying when we are dealing with a respiratory pathogen like SARS-CoV2 where you are infectious up to 5 days before symptoms appear (subclinical infectious period).


Distance

The closer you are to another human, the more risky your conversation or interaction is. Maintaining social distancing of 2 meters (6 feet) allows large droplets to fall to the ground. Your risk is primarily from the virus contained in the small droplets, but the further away you are, the more chance there is for these small particles to disperse in the air, resulting in a lower viral load, and lower risk.

Time.

The longer you talk face-to-face with someone, the more likely you are to accumulate an infectious viral load (dose) of the virus.

Location or Place.

Indoors vs. outdoors. Respiratory droplets fall to the ground at the same rate indoors as outdoors. What changes is the distance they travel before they fall to the ground. Wind and air conditioners/fans can push large droplets farther away from people who are speaking. Be aware of which way the wind or A/C is blowing. Try to speak perpendicular to the wind if possible so that the air pushes the particles away from both of you and not in the direction you are speaking.


Masks - Wearing a mask while breathing, talking, shouting, coughing, or sneezing traps respiratory droplets coming out of your nose and mouth. Even with the most basic mask, 100% of large and medium respiratory droplets will be trapped inside the mask. As masks become higher in quality, the amount of small respiratory droplets and core (smallest) droplets that will be trapped also increases.

The quality of the mask includes:

  • How tight does it fit on the face?
  • How much air passes through the fabric (versus towards your eyes/lenses)
  • The type of fabric used in the breathing area of ​​the mask.


Despite all the publications on mask usage, there are no hard numbers to present. Every mask is different, and the way people use masks is different. That's why it's so hard for scientists to quantify what a mask should be made of and how effective each type of mask is. Above all, we scientists like to be precise, but that's not possible when there are so many confounding variables.

At a minimum, a mask is believed to reduce 50% of the mask's emissions. Masks that have multiple layers of fabric can be up to 90% effective at reducing emissions (reference).

I want to emphasize that there is no clear evidence to indicate that cloth masks will protect you from inhaling the smallest respiratory droplets (those core droplets) from another person. The primary purpose of a homemade mask, when worn by everyone, is to mitigate the source of the emissions. If we decrease the respiratory droplets coming out of us, we can substantially decrease the amount of virus we emit into the air, thereby decreasing the risk to everyone.

My mask protects you - Your mask protects me


Summary of face-to-face conversations:

  • When we socially distance ourselves at 6 feet (2 meters), conversations are less risky because most large respiratory droplets fall to the ground before reaching the other person.
  • Wearing a mask reduces the amount of respiratory droplets and core droplets (the smallest ones) released into the air.


Successful infection = (Exposure to virus) x (Time)

If we can reduce the amount of virus released into the air in respiratory droplets by wearing masks, we will increase the time we can have safer face-to-face conversations.

Shared Spaces

I have already discussed the problem with enclosed spaces in detail (see the article “Risks and how to avoid them” https://www.erinbromage.com/post/the-risks-know-them-avoid-them).

We know that shared spaces increase the risk of infection with:

  • The number of people in that space.
  • The amount of time we spend in that space.
  • Closed spaces are more risky than open-air spaces (due to lack of air exchange in closed spaces).


What is the role of masks in closed spaces?

Indoor spaces allow the virus to accumulate in the air if there is no adequate filtration and air exchange.

In indoor environments with little air exchange and filtration, infected respiratory droplets can spread around the room, accumulate in the air, and after enough time, people sharing that space can inhale enough viral load to become infected. However, with the use of masks, respiratory emissions are reduced and you can safely spend a longer period of time indoors.

I am an employee/employer where I spend a lot of time in shared spaces, what can I do?

  • Invest in high-quality masks. Look for a mask that has multiple layers and a multi-fabric design and an adjustable nose bridge to seal the top of the mask to your face. The more exhaled air that is forced through the mask (and not into your eyes), the more respiratory droplet filtration will be trapped inside the mask and everyone will be safer.
  • Improve air exchange with the outside: The more air you can exchange with the outside, the lower the viral load in your space.
  • Improve filtration: Some A/C systems can be easily upgraded by incorporating HEPA filters. UV in AC ducts is also improved. Consider purchasing portable HEPA filtration systems for smaller spaces where a central air system may not be adequate (therapy offices, treatment spaces, etc.).


I advise company managers to read this article on “healthy buildings” by Harvard professor Joseph Allen Prof. Joseph Allen, to get ideas on how to engineer a safer space.

So the next time someone sends you a mask meme, you know how to respond.

  • Masks are part of the solution to reduce the release of the virus into the environment, but they are not 100% effective.
  • Social distancing works outdoors and for brief indoor gatherings, but just using social distancing indoors won't protect you from infection.


Wearing a mask is a social contract. My mask protects you, your mask protects me. But masks are not perfect and must be used in conjunction with other infection mitigation measures such as physical distancing and handwashing. There is ample evidence to suggest that universal mask use significantly reduces transmission of respiratory viruses. Mask use is grounded in biology and can have a real effect on reducing infection transmission, protecting your co-workers and at-risk people in your community.

Even 102 years ago, people understood that wearing masks was part of the solution and it was a social contract to protect your neighbor. This photo was taken in 1918 during a Georgia Tech football game during the Spanish Flu outbreak. The other photo was taken last week, and it happened because mask wearing was politicized in the US.


My mask protects you; Your mask protects me.

Additional Thoughts

  • Inhalation Filtration: I decided not to touch on the topic of inhalation filtration capacity of masks. I want to focus on Your mask protects me, My mask protects you. Even the most basic masks do this.
  • Do my cloth masks protect me too? Yes, some brands provide filtration capabilities on exhalation and inhalation, but their effectiveness comes down to how well they fit your face and the material used.
  • Masks with valves: These allow respiratory droplets to be ejected through the valve, possibly at a higher rate than normal breathing and thus dispersing the droplets further. While the valve filter does protect you from infection and the masks do trap larger droplets, they are not the best option when considering a community approach to mask use. They protect you but not your neighbor as much.
  • Why not use an N95 or KN95 mask? These high-quality respirators provide excellent protection for exhalation and inhalation, but only if they fit the face properly, and they are not easy to fit properly. All air must pass through the respirator material, and the vast majority of people who wear them do not wear them correctly.
  • Wash your mask regularly: Especially if you are using it for long periods of time. Soap and water is enough. See my March 30 March 30th post on masks for other tips and tricks.

I found many very good articles on how to use masks. If you want to read them here:

  • New article published on the 27th May And a new article published on the 27th May