One popular style of face covering may not be doing much to limit spread of the coronavirus, according to a study out of Duke University.
The researchers found that while most of the cotton, cloth or surgical-style masks tested were effective at limiting the amount of respiratory droplets a person expelled while talking, the “neck gaiter” or neck fleece actually resulted in more small droplets being expelled.
“We attribute this to the fleece, the textile, breaking up those big particles into many little particles,” Martin Fischer, an associate research professor at Duke said in a news release.
The novel coronavirus that causes COVID-19 is spread from person-to-person mostly through respiratory droplets that we all expel out of our mouths when we talk, sneeze, cough or breathe heavily, according to most experts.
Fischer said it’s possible that releasing more small droplets through a thin mask is worse than expelling larger droplets with no shield at all.
“[The smaller particles] tend to hang around longer in the air, they can get carried away easier in the air, so this might actually be counter productive to wear such a mask,” Fischer said. “It’s not the case that any mask is better than nothing. There are some masks that actually hurt rather than do good.”
However, some have said that conclusion is premature and we don’t have enough information to declare that those masks do more harm than good. Slate news director Susan Matthews points out that the researchers tested only a single subject with the gaiter-style mask, increasing the chances that the mask simply didn’t fit, or that there was some other issue with either the mask or the test subject.
The subject also only repeated the short phrase “stay healthy, people,” 10 times for each mask. The subject did not speak in different volume levels, cough, sneeze or simulate other conditions like heavy breathing during exercise. Gaiter masks are very popular among runners because of their lightweight construction and looser fit.
A study out of the University of Wisconsin-Madison from July found that gaiters were more effective than other types of masks at catching droplets from a simulated cough, but that study used “snug-fitting” homemade gaiters made of tightly woven fabric with a metal nose-piece and elastic to ensure a good fit.
Matthews also notes that we don’t know whether a person expelling a higher number of small droplets is more likely to spread the disease than a person producing fewer, larger blobs of virus-laden spittle.
The findings of the Duke team were published online last week in Science Advances, a peer-reviewed journal.
Fisher and the team at Duke tested 14 different kinds of masks using cardboard, laser lights and a cell phone camera, as you can see in the short video below.
The subject repeats the same phrase into the contraption, first with no mask, then with the different styles of masks to see which were most effective. The laser makes the droplets coming out of a person’s mouth visible and the camera records those droplets to be counted.
The team found that surgical masks, as well as cotton, cloth and polypropylene masks were effective in blocking the droplets from being spread when the subject spoke in a normal voice. The best-performing masks were the medical-grade N95 masks — without valves — used by medical professionals.
The neck fleece (Mask #11 in the photo above) actually resulted in more droplets being counted. The bandana reduced the number of droplets by about half, the others reduced the droplet count to 20 percent or less of the mask-less count.
One of the researchers told The Washington Post that the gaiter that tested poorly was made of a lightweight, polyester spandex material, marketed as a breathable item for outdoor sports activity.
“If you can see through it when you put it up to a light and you can blow through it easily, it probably is not protecting anybody,” Warren S. Warren, a co-author of the paper told the Post.
N95 medical masks with valves performed about as well as cotton masks, with the researchers noting the valves were designed to keep droplets from entering the mask from the outside, not to stop the person wearing the mask from expelling droplets that others could then breathe in.
The overall takeaway from the paper is clear, however. While some masks perform better than others, most masks are effective at reducing the droplets that spread the coronavirus.
“Wearing a mask is a simple and easy way to reduce the spread of COVID-19,” Dr. Eric Westman, a Duke physician who worked with Fischer to design the experiment, said in a news release. “About half of infections are from people who don’t show symptoms, and often don’t know they’re infected. They can unknowingly spread the virus when the cough, sneeze and just talk.
“If everyone wore a mask, we could stop up to 99% of these droplets before they reach someone else. In the absence of a vaccine or antiviral medicine, it’s the one proven way to protect others as well as yourself.”
This study was designed as a proof-of-concept of the researchers’ technique to measure droplet spread. The researchers say further research is needed to test different masks under a variety of conditions, such as speaking at different volumes, or coughing and sneezing.
“We certainly encourage everyone to wear a mask, but we want to make sure that when you wear a mask and you go to the trouble of making a mask, you make one or wear one that actually helps not just you but helps everyone,” Fischer said.
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