By Elizabeth Kim
A Duke university study of 14 different types of face masks by scientists has yielded some surprising findings about the efficacy of different face coverings, while also undermining the assertion that any mask or face covering is better than none.
In a test, researchers found that speaking into some masks, particularly a neck fleece or gaiter often worn by runners, actually dispersed the largest droplets of potential virus into small droplets. The study examined the degree to which masks blocked droplets from entering the air, not whether the mask successfully blocked droplets from entering the mouth of the mask wearer.
"Considering that smaller particles are airborne longer than large droplets (larger droplets sink faster), the use of such a mask might be counterproductive," researchers wrote in the study, which was published Friday in Science Advances.
Overall, a fitted N95 tied with a surgical mask for best performance in terms of minimizing the number of droplets spewing into the air. In fact, the three-layer surgical mask, which may look flimsy to some, was nearly as good as the N95, which is considered by many to be the gold standard of face masks. Depending on the type of material, cotton masks also tested decently well.
Knitted masks and bandanas performed the most poorly. Fleece masks, as mentioned above, were rated worse than wearing no mask at all.
Overall, the fit of a mask also turned out to be very important. A so-called valved N95 mask was significantly worse than a fitted N95.
The new study comes as the pandemic has spawned a new industry of washable cloth and designer face masks. Since late April, New York City has been handing out free surgical face masks to New Yorkers in various locations, including city parks. In accordance with guidance from the Centers for Disease Control and Prevention, Mayor Bill de Blasio has suggested that scarves or homemade fabric masks can be worn in lieu of a surgical mask, which can be easily soiled. Although some health authorities advise against reusing surgical masks, de Blasio has said that the masks can be washed and reworn.
In an interview with the Boston Globe, Warren Warren, a professor of physics, chemistry, and radiology who was one of the co-authors of the study, said individuals should study the material of a face mask. "If you have a mask and you can see through it in the light and you can blow through it, it’s probably not a very good mask," he said.
Public health experts have said face masks can significantly reduce the spread of the virus. Members of the White House coronavirus task force have implored Americans in recent weeks to wear them, especially in parts of the country where the virus is surging. President Donald Trump, however, has rarely worn a mask in public.
One new model has projected that 66,000 U.S. lives could be saved if 95% of all Americans complied with the face mask recommendation. At least 163,000 people in the country have died from coronavirus. University of Washington scientists expect that number to soar to nearly 300,000 by December.