There’s been a dust up in the running world about the recent study from Duke University looking at the effectiveness of gaiters as a protective garment in the era of Covid, and covered by multiple secondary articles including Fast Company and The Washington Post, as well as gaining social media traction.
So we reached out to our very own researcher and Volée member Dr. Taisa, author of Running and the Science of Mask Wearing that became a favorited and popular blog for the running community back in April, at the start of the COVID outbreak.
Taisa’s reply to the latest gaiter research is below.
In short: You don't need to throw out your gaiters!
What's the Duke study all about?
The goal of the Duke University study led by Dr. Martin Fischer, Associate Professor in Chemistry, was to devise a simple method for evaluating mask performance as measured by droplet transmission. Specifically, they measured the number of particles over 0.5 that are transmitted at a 20cm distance while an individual says "Stay healthy, people". The paper provides a proof-of-concept study for their proposed setup that uses relatively cheap equipment (a cell phone, laser, a box) to estimate the total transmitted droplet count. In their setup, an individual speaks into a box in the direction of laser beam that has been expanded into a sheet. When droplets go through the light sheet, they scatter the light, and this scattering is recorded by a cell phone camera. Then, a computer algorithm is used to count the droplets in the video. It's a cool study!
While they evaluate their protocol on various types of masks, this is done to demonstrate their methodology of particle counting. The study is not intended to study effectiveness of masks. Nor do the authors claim it does: "The mask tests performed here should serve only as demonstration" (of the protocol). Unfortunately, numerous media outlets have interpreted this as a definitive study on mask effectiveness, which has led to controversy.  

The 14 commonly available masks the Duke University research team tested their proof-of-concept protocol for measuring droplets transmitted while speaking on. You can see the gaiter (denoted "neck fleece") tested in (11). Photo credit: Emma Fischer, Duke University

So where did the "Gaiters are worse than no mask" claim come from?
In the study, the authors report droplet transmission from masks as a percentage relative to a baseline measurement of someone talking without a mask (taken as 100%). They find, similar to numerous other studies, that not all coverings are equally effective: medical-grade non-valved N95 respirators transmitted below 0.1% of particles, various cotton masks transmitted about 20% of particles, and the gaiter transmitted 110% of particles. The authors hypothesize that this result is due to the gaiter "dispersing the largest droplets into a multitude of smaller droplets" which could linger in the air longer. This hypothesis is reasonable though it isn't tested, and, more importantly, it does not necessarily mean infection risk increases (more on that below). Unfortunately, this single 110% point has been extrapolated from and is now being used as definitive evidence that "gaiters are worse than no mask".

Figure taken from the Duke University study: "Droplet transmission through face masks, displayed on a logarithmic scale. Relative droplet transmission through the corresponding mask. Each solid data point represents the mean and standard deviation over 10 trials for the same mask, normalized to the control trial (no mask), and tested by one speaker. The hollow data points are the mean and standard deviations of the relative counts over four speakers."

Wait, but 110% is more than 100%? Doesn't that mean gaiters are "worse" than no mask? Am I hurting people by wearing my gaiter?
No, that's highly unlikely and there are a few reasons for this:
  1. A single test subject and mask is not conclusive data: Since this goal of this paper was to demonstrate their particle counting methodology not rigorously test mask efficacy, most masks, including the gaiter, were tested on just one individual. They refer to him as "a male test person with a strong voice but without shouting". While this works fine for demonstrating methodology, with respect to providing results on mask efficacy it serves more as anecdotal evidence rather than data. There is no guarantee that the person spoke at the same loudness/forcefulness for each test, or that you would see similar results for other individuals. In fact, the authors even note: "the mask tests performed here should serve only as a demonstration. Inter-subject variations are to be expected, for example due to difference in physiology, mask fit, head position, speech pattern, and such." To do a thorough study, you'd need to design a specific study with multiple trials of at least 7-10 people, testing transmission at multiple distances and for a variety of activities (breathing, coughing, talking).
  2. We don't know specifics of the gaiter or how it was worn: We know lots of factors affect gaiter and mask efficacy including fabric, fit, thickness, if it's folded over, etc. For the gaiter in question, we have a photo which appears to be a "standard" thin single-layer gaiter, like the ones you might get in a race swag bag, but we don't know much else. Thus, extrapolating these results to all gaiters isn't valid.
  3. The study is not looking at "real world" conditions of people running with gaiters: The set-up measures particles at 20cm distance when a man says the phrase "Stay healthy, people.” It says nothing to support the idea “if a runner runs past you at a 6ft distance wearing a different gaiter, it is worse than nothing.” Since droplets produced while breathing are not the same as when talking, this is another variable that makes drawing definitive conclusions a stretch. Furthermore, the study was also someone talking into a box, so again, very different from being outside where you have environmental factors at play (transmission has been shown to be much worse indoors than outside).
  4. Change in particle numbers does not necessarily equate to change in infection spread: While the number of transmitted particles provides a fine proxy for virus transmission, it does not equate to change in infection spread. To study changes in infection spread would be much harder, requiring identifying individuals with Covid-19 (again, at least 7-10), place them in a negative pressure room, have them cough, breathe, and talk with different masks on and culture the virus that is transmitted to see how much difference each mask makes. You'd want to do this at different distances and with some standardization on how people "cough, breathe and talk", and lots of other controls in place too. You can imagine this is tough and requires lots of time, medical ethics review, and money so this is why we see so many studies measuring "change in particles": you can approximate this with non-sick individuals, and we assume that on some level, fewer particles is better. However, this is a large approximation since we don't know how much virus would theoretically be carried in each of these particles, how much we need for infection, or the impact in terms of infection risk of shearing a large particle into smaller ones. (eg. Is a smaller particle more likely to be breathed in by a passerby, or more likely to be carried away in the wind? Is the dose enough to cause infection? Is it better or worse than a larger particle falling onto a surface? There are a lot of questions science has yet to answer before we can say what's better or worse!)
So what can we conclude?
As with anything else, "definitive" headlines are often misleading. It's easy for part of a single study, with limited parameters, to be picked up and extrapolated in a way that alarms people. For this Duke study, we can simply reiterate what we already know: not all masks are created equal. Thin and poorly fitting face coverings (eg thin gaiters and bandanas) will not protect as well as well-fitting double layer coverings, surgical masks or N95s, but there is no conclusive evidence that a gaiter is worse than no mask. Opting for a fabric with a tighter weave, a thicker fabric, and masks with double-layers is always a good rule of thumb for any face covering, mask or gaiter!
Dr. Taisa Kushner (PhD, not MD) is a Computing Innovation Fellow at Oregon Health and Sciences University Medical School, and part of the Federation of American Scientists’ COVID-19 Ask A Scientist team. Please contact with any questions or comments on the content of this article!
Taisa Kushner
Tagged: social


Wait a minute,, older female scientist!!!
This means you are informing yourself, using commons sense, and making decisions and taking actions base on both. (without hurling insults at people who don’t agree)

I’m not completely sure this is even allowed at this point. ;)

We will keep our gaiters too.

— Amanda Campbell

I guess you can’t count on scientists from NC understanding that fleece is a thing, and that it’s not the correct term for the object they tested. But regardless of their nomenclature error, their experiemental design was, as you point out, not particularly rigorous. The plural of anecdote — which is basically what this “study” was — is not, and never will be, data.

I’m an older female scientist who does not have a loud voice. I plan to wear my various neck gaiters (polyester Buffs, a heavy woolen one, and others I made myself out of actual heavyweight fleece) to cover my mouth and nose as I silently pass other hikers and skiers here in Alaska this fall and winter. I wear them doubled over. And I’ll continue to wear my home-made multi-layer custom-fitted batik quilter’s cotton face masks when I need to be indoors with other people outside my home.

— AK