Tuesday, July 7, 2020
A new study led by University of Arizona researchers examines a variety of “nontraditional mask materials” and their ability to protect wearers. The study, published in the Journal of Hospital Infection, compares the risk reduction of materials like scarves, pillowcases, and t-shirt fabric, as well as more common professional masks.
"N99 masks, which are even more efficient at filtering airborne particles than N95 masks, are obviously one of the best options for blocking the virus, as they can reduce average risk by 94 to 99 percent for 20-minute and 30-second exposures, but they can be hard to come by, and there are ethical considerations such as leaving those available for medical professionals," said lead author of the study Amanda Wilson, who works as an environmental health sciences doctoral candidate in the UA’s Department of Community, Environment and Policy.
Other than professional N99 and N95 masks, the researchers found that vacuum cleaner filters — which can be inserted into cloth masks — are one of the best household options. In the study, vacuum cleaner filters reduced infection risk by 83 percent for a 30-second exposure and 58 percent for a 20-minute exposure. Scarves reduced infection risk by 44 percent after 30 seconds and 24 percent after 20 minutes. Cotton t-shirt fabric was found to be “only slightly better than wearing no mask at all.”
As for the efficacy of masks in general, the researchers found that wearing anything from a simple scarf mask to an N95 (as compared to no mask at all), reduced risk infection anywhere from 24 to 94 percent.
"The denser the fibers of a material, the better it is at filtering. That's why higher thread counts lead to higher efficacy. There's just more to block the virus," Wilson said in a press release. "But some masks (such as those made from silk) also have electrostatic properties, which can attract smaller particles and keep them from passing through the mask as well."
Infection risk increased as exposure duration increased, hence the 30-second and 20-minute trials. The greatest reduction in estimated infection risk was for FFP3 masks, which reduced baseline risks by 94 percent for 20-minute exposures and 99 percent for 30-second exposures.
Another factor in mask efficacy is proper positioning; masks should have a good seal that tightens on top of the nose, and masks shouldn’t be worn beneath the nose.
"Proper use of masks is so important," Wilson said. "Also, we were focusing on masks protecting the wearer, but they're most important to protect others around you if you're infected. If you put less virus out into the air, you're creating a less contaminated environment around you.”