The Great Mask Debate

Virus size vs pore size

To determine which type of mask is appropriate, we first need to look at the size of the virus. Researchers have established that there is a range of sizes of the coronavirus in an aerosolized form. However the average is 100nm or 0.1 microns (Pubmed: Nano-aerosols). Since this is a respiratory virus, it is known to attach to particles and droplets. When an infected person is breathing, these droplets can be released into the air. Imagine seeing your breath during a cold winter’s day, except this happens every time you breathe.

So what’s the problem then?

While NIOSH has standardized N95 and N98 at 300nm, to-date there is no filter standards, nor special filter technologies, tailored for capturing airborne viruses and 100nm nano-aerosols.

Pubmed: Electrostatic Charged Nanofiber Filter for Filtering Airborne Novel Coronavirus (COVID-19) and Nano-aerosols

So even though we don’t have technology to capture the 100nm particles, there is still hope. The way that the N95 masks are designed is a weave of multiple different layers. It forms a maze for the particles to get trapped in.

Enter the N95 (for Healthcare workers)

An FDA approved “NIOSH N95” mask filters “95 percent of particles that are 0.3 microns in size or larger”. In order for the N95 to work effectively it needs to have a tight seal. Any air that can escape the sides or the top is not being filtered.

An N95 respirator is a respiratory protective device designed to achieve a very close facial fit and very efficient filtration of airborne particles. Note that the edges of the respirator are designed to form a seal around the nose and mouth. Surgical N95 Respirators are commonly used in healthcare settings and are a subset of N95 Filtering Facepiece Respirators (FFRs), often referred to as N95s.

FDA: N95 respirators and Surgical masks

Surgical masks

The average surgical mask pore size is between 0.3-10 μm (microns). While this is bigger than the size of the virus, it is the appropriate size to catch bodily fluids like saliva that the virus is more likely to be bound to. Surgical masks can filter up to 95% of viral particles. The protection is not for the wearer (Pubmed: Facial protection for healthcare workers). However, the main difference between N95s and Surgical masks is the fit. Loose fitting surgical masks prevent a tight fit around the face. Any air escaping the top or sides and not physically passing through the mask will not be filtered.

If worn properly, a surgical mask is meant to help block large-particle droplets, splashes, sprays, or splatter that may contain germs (viruses and bacteria), keeping it from reaching your mouth and nose. Surgical masks may also help reduce exposure of your saliva and respiratory secretions to others.

FDA: N95 respirators and Surgical masks

Cotton masks

Cotton masks will have a wider range of pore sizes depending on the specific fabric being used. While we can’t put each individuals mask under a microscope, we can provide a range 80 to 500 μm. This was based on research done in 2019 to test cloth masks that were being used in developing countries (Pubmed: Nepal research). These were used for particle filtration where masks that filter 2.5 μm or less (PM_2.5) are not easily accessible.

But the CDC says…

N95 vs surgical vs cotton

The CDC recommends the use of cotton masks. Originally, this was from the standpoint of limited supply of N95 and surgical masks available for healthcare workers. However, this was from a few months ago before the factories were able to scale up production.

The average person going to the grocery store doesn’t need an N95. Surgical masks should replace cotton masks as the availability has increased.

My how quickly things change

I started writing this section in the morning on June 28, 2020. The last update to the CDC website was May 28, 2020. The CDC then updated the website in the afternoon of June 28, 2020. It’s amazing to see how much has changed.

As of May 28th, 2020:

# of cotton mask specific resources = 0

If you go to the CDC’s website on Cloth Face Coverings, at first glance it looks great. They give you a paragraph or two about wearing masks where social distancing is not possible. Pair that with a video from the US Surgeon General on how to make a cloth napkin mask. Add a dash of resources with great titles including the dreaded term “Asymptomatic”.

If you take it for face value, it’s easy to understand why wearing cloth masks is wide spread. However, if you do a quick 5 minute keyword search through those sources you will find something interesting. By using “face”, “mask” or “cloth”, you will find that NONE of the resources mention the use of cloth masks.

In addition, only one source references masks and they recommend N95 “or face mask if not available.” (SARS-CoV-2 Long-Term Care Skilled Nursing Facility). They stated that for health-care workers cloth masks should be a last resort.

The CDC webpage gives you circular references. Want to learn more about “Use of Cloth Face Coverings to Help Slow the Spread of COVID-19”? Well this takes you to a page that gives you absolutely no references at all!

June 28, 2020 update:

# of cotton mask specific resources = 5

Bravo! More sources this time, and even a handful of them use the keywords “face”, “mask”, or “cloth”.

There is an article citing the use of cloth facemasks by the CDC… their own article: CDC article. In this article the primary source for the cloth mask reference is #37: Covid-19: What is the evidence for cloth masks?

Note: When you follow on to the primary source it quickly shows a different standpoint

The evidence is not sufficiently strong to support widespread use of facemasks as a protective measure against covid-19. However, there is enough evidence to support the use of facemasks for short periods of time by particularly vulnerable individuals when in transient higher risk situations.

The BMJ: Covid-19: What is the evidence for cloth masks?

Droplet size source

Another resource goes into testing the droplet size while talking (Pubmed: Visualizing Droplets). Droplets were between “20 to 500 μm” in size, which suggests that cotton masks would only catch the larger size droplets. Best case scenario, only those < 80μm would pass through. Worst case scenario, the cotton masks would catch only the largest 500 μm particles.

Testing homemade masks

Although any material may provide a physical barrier to an infection, if as a mask it does not fit well around the nose and mouth, or the material freely allows infectious aerosols to pass through it, then it will be of no benefit.

Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?

Another source the CDC provides states that the efficacy of homemade masks showing a combination of different fabrics. Even the best homemade cloth masks can go from 80% down to 38% efficiency, with an improper seal. This is why N95 masks are fit-tested (Pubmed: Aerosol and Cloth Masks).

The final source that they gave is further explained in “Droplet testing” of this post. Fabric holds up well in research settings, but taking these results and applying them to real world scenarios is different.

Real-world context

On a regular basis I see the typical mask on the chin and smoking while wearing a mask. The mask under the nose, or bandana/scarf that allows the air to flow out the top or bottom. Compliance is difficult to maintain in a society not used to mask wearing. However, in other countries, like China, every flu season surgical mask wearing in the norm.

Indoor vs Open-air spaces

The problem with indoor spaces is the lack of air filtration and central air circulation. At home this can be addressed by the use of HEPA filters. HEPA filters can provide the same level of filtering as an N95 (down to 0.3 microns). For larger buildings the MERV 13 filter also works on an equivalent level, helping to reduce the viral load in the air when it’s recirculated (Video: Harvard Health). Also bringing in fresh outside air while exhausting inside air can be helpful.

Breathing in a well ventilated area means that the ability for the virus to dissipate is greatly increased. Respiratory droplets are released but they are not further concentrated like they would be indoors.

So why are some people wearing masks while running by themselves?

If they are wearing masks to reduce air pollution from motor vehicles, or to reduce allergens this makes sense. However, if it is to prevent against viral infection, this falls apart.

“Consider conducting the activity location with greater ventilation and air exchange (for instance, outdoors versus indoors) and where it is possible to maintain physical distance from others.”

CDC: Considerations updated June 28, 2020

Bait and switch

The media has played a large role in the classic bait and switch technique relating to the efficacy of masks. For example, in one clip the news anchor will show the production of N95 masks in a 3M factory and talk about the 95% blockage that the masks provide. Follow this up with a transition to how shops on Etsy are blowing up with sales of cotton masks, and now what do we have?

You now equate the 95% filtering rate of the N95 masks, with the cute mask that you bought on Etsy or made at home. While the masks can make a great statement such as “Black Lives Matter” or “DC should become the 51st state”, these logos and patterns do not deter the virus.