Not all face masks are created equal. Scientists have recently devised a simple experiment to see which type of face mask — ranging from homemade cotton masks and bandanas to N95 masks worn by medical workers — did the best job of stopping droplets from spewing out of people's mouths and noses. While most proved to be effective at reducing some droplets of saliva from flying into the surrounding environment, a few of the face masks actually seem to make things worse by causing droplets to spray out more. 

The findings were reported in the journal Science Advances last week. 

Perhaps unsurprisingly, the best face coverings were N95 masks (without valves), the hospital-grade type of masks used by frontline medical workers, followed by surgical masks, polypropylene masks, and cotton-polypropylene masks.

Cloth face masks were shown to be fairly effective at blocking the droplets. However, bandanas and neck fleeces didn’t block the droplets much at all and barely performed better than no mask. In fact, the neck fleece seemed to disperse the largest droplets into a multitude of smaller droplets, which arguably means it's worse than wearing no mask at all.

To reach these conclusions, a multidisciplinary team from Duke University in North Carolina created a set-up consisting of a dark room, a box, a few lasers, a lens, and a smartphone camera. This method allowed the researchers to see how the face-covering affected the flow of saliva and mucus droplets spraying from the person’s mouth and nose while they talked. 

The scientific debate around the effectiveness of face masks proved remarkably controversial. Ever-changing guidelines have sowed confusion among the public about the effectiveness of masks, but most experts now agree that face coverings play an important role in preventing the spread of Covid-19. 

As this new study shows, it’s perfectly clear that simply talking does spew out droplets into the surrounding environment, which could potentially be inhaled by a close bystander. While this does not go into the likelihood for an infected person to spread Covid-19, it’s known that respiratory droplets such as these can transmit respiratory viral infections, especially in poorly ventilated areas. 

“We confirmed that when people speak, small droplets get expelled, so disease can be spread by talking, without coughing or sneezing,” Martin Fischer, Associate Research Professor in the Department of Chemistry at Duke, said in a statement. “We could also see that some face coverings performed much better than others in blocking expelled particles.”

^{Inexpensive, accessible device provides Visual proof that masks block droplets. Duke Health/Fischer et al., 2020, Science Advances}

“This was just a demonstration – more work is required to investigate variations in masks, speakers, and how people wear them – but it demonstrates that this sort of test could easily be conducted by businesses and others that are providing masks to their employees or patrons,” Fischer added.

“Wearing a mask is a simple and easy way to reduce the spread of COVID-19,” co-author Eric Westman said. “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 they cough, sneeze, and just talk."

If you want to further appreciate the benefits of face masks and the spread of Covid-19, you can look beyond lab experiments at the epidemiologic data (the incidence and transmission of the diseases across a population in the real world). In perhaps the most simplistic example of this, one study looked at 198 countries across the world and found that those with cultural norms or government policies favoring mask-wearing had lower death rates from Covid-19 than those that didn't and were struggling to implement them.