A new study at Duke University compared 14 types of masks to see which are the most effective at reducing the spread of the coronavirus.
Neck masks and bandannas, they found, might actually make things worse.
The researchers tested how effective each mask was at reducing the number of respiratory droplets transmitted during speech — the kinds likely to carry viral particles.
They tested surgical masks, N95 masks, cotton masks, and polypropylene masks, as well as homemade alternatives such as neck fleeces and bandannas. The study involved a test group of people speaking 10 times while wearing each of these masks and a control group of people not wearing any masks.
The researchers found that most of the masks reduced the number of respiratory droplets transmitted compared with the control group, adding to the body of evidence that masks are important in helping to limit the spread of the coronavirus. They found that polypropylene masks transmitted a similar number of droplets as surgical and N95 masks, which transmitted the fewest droplets.
The neck fleece and bandannas, however, had higher counts of respiratory droplets. In fact, the researchers found that the neck fleece increased the number of respiratory droplets by creating several smaller droplets from larger ones, resulting in more droplets than not wearing masks at all.
The study said that since smaller droplets can stay in the air longer than larger droplets, a neck fleece "might be counterproductive."
SPARTA, KENTUCKY - JULY 09: Jeb Burton, driver of the #8 Rocky Boots Chevrolet, and Ross Chastain, driver of the #10 Chevy Accessories Chevrolet, talk on the grid prior to the NASCAR Xfinity Series Shady Rays 200 at Kentucky Speedway on July 09, 2020 in Sparta, Kentucky. (Photo by Jared C. Tilton/Getty Images)