Some face coverings, like neck gaiters, are actually worse than going without a mask, breaking down large droplets into smaller particles and allowing them to escape, Duke University researchers discovered in a study released on Friday.
Researchers at Duke University examined several types of face coverings — from cloth masks to bandanas to neck gaiters — to review their effectiveness of stopping large respiratory droplets. Determining the effectiveness of masks, they said, “is a complex topic,” in part, because “the infection pathways for COVID-19 are not yet fully understood and are complicated by many factors such as the route of transmission, correct fit and usage of masks, and environmental variables.”
Nonetheless, several states, local governments, and businesses have implemented mask mandates to help slow the spread of the novel coronavirus, despite the lingering questions on the efficacy of homemade masks, which many Americans have embraced given the widespread call to reserve N95 masks for frontline medical workers.
The researchers tested 14 different face coverings, with the wearer speaking “into the direction of an expanded laser beam inside a dark enclosure.”
“Droplets that propagate through the laser beam scatter light, which is recorded with a cell phone camera. A simple computer algorithm is used to count the droplets in the video,” researchers explained.
While the study showed an N95 proving to be the most effective, it also found fleece coverings and neck gaiters to be worse than going maskless, as they break down larger respiratory droplets, creating smaller droplets which can escape.
Per the study:
We noticed that speaking through some masks (particularly the neck fleece) seemed to disperse the largest droplets into a multitude of smaller droplets (see Supplementary Fig. S5), which explains the apparent increase in droplet count relative to no mask in that case. Considering that smaller particles are airborne longer than large droplets (larger droplets sink faster), the use of such a mask might be counterproductive. Furthermore, the performance of the valved N95 mask is likely affected by the exhalation valve, which opens for strong outwards airflow. While the valve does not compromise the protection of the wearer, it can decrease protection of persons surrounding the wearer. In comparison, the performance of the fitted, non-valved N95 mask was far superior.
Bandana masks and knitted masks also proved to offer little protection.
“We were extremely surprised to find that the number of particles measured with the fleece actually exceeded the number of particles measured without wearing any mask,”Martin Fischer, an author of the study, told CNN.
“We want to emphasize that we really encourage people to wear masks, but we want them to wear masks that actually work,” he added.
While the study found surgical masks and cotton masks to be relatively effective in reducing respiratory droplets, the effectiveness of makeshift face coverings continues to remain largely inconclusive and a subject of heavy debate. Even the Centers for Disease Control and Prevention (CDC) has failed to state definitively that homemade masks work to curb the transmission of the novel coronavirus, stating that it “may” help prevent the spread of the virus.
An April commentary from two experts on respiratory protection — both a retired and current professor at the University of Illinois at Chicago — referenced the National Academies of Sciences Rapid Expert Consultation on the Effectiveness of Fabric Masks for the COVID-19 Pandemic (NAS 2020), which noted the lack of evidence of fabric masks filtering out smaller, aerosolized particles.
The evidence from … laboratory filtration studies suggests that such fabric masks may reduce the transmission of larger respiratory droplets. There is little evidence regarding the transmission of small aerosolized particulates of the size potentially exhaled by asymptomatic or presymptomatic individuals with COVID-19.
“Wearing a cloth mask or face covering could be better than doing nothing, but we simply don’t know at this point,” the experts said.
While they said they made it clear that they support mask-wearing, they added that they:
…continue to conclude that cloth masks and face coverings are likely to have limited impact on lowering COVID-19 transmission, because they have minimal ability to prevent the emission of small particles, offer limited personal protection with respect to small particle inhalation, and should not be recommended as a replacement for physical distancing or reducing time in enclosed spaces with many potentially infectious people.
We are very concerned about messaging that suggests cloth masks or face coverings can replace physical distancing. We also worry that the public doesn’t understand the limitations of cloth masks and face coverings when we observe how many people wear their mask under their nose or even under their mouth, remove their masks when talking to someone nearby, or fail to practice physical distancing when wearing a mask.
However, the commentary was updated on July 16 with the following editor’s note:
The authors and CIDRAP have received requests in recent weeks to remove this article from the CIDRAP website. Reasons have included: (1) we don’t truly know that cloth masks (face coverings) are not effective, since the data are so limited, (2) wearing a cloth mask or face covering is better than doing nothing, (3) the article is being used by individuals and groups to support non-mask wearing where mandated and (4) there are now many modeling studies suggesting that cloth masks or face coverings could be effective at flattening the curve and preventing many cases of infection.
Similarly, a study from the New England Journal of Medicine titled, “Universal Masking in Hospitals in the Covid-19 Era” explicitly stated, “We know that wearing a mask outside health care facilities offers little, if any, protection from infection,” and emphasized the psychological benefits of universal mask-wearing.
However, the study provided an update on June 3, affirming that the “intent of our article was to push for more masking, not less.”
The update read in part:
We did state in the article that “wearing a mask outside health care facilities offers little, if any, protection from infection,” but as the rest of the paragraph makes clear, we intended this statement to apply to passing encounters in public spaces, not sustained interactions within closed environments.
Nine out of ten Americans indicated that they have “always” or “sometimes” worn a mask in public over the course of the last month, a recently released Morning Consult survey showed. A Morning Consult/Politico survey released last month also revealed that the vast majority of voters would support their states implementing a mask mandate that threatened fines and jail time for violators.