During the COVID-19 pandemic, cloth face masks have become a way to protect oneself and others from the virus. And for some people, they have become a fashion statement, with so many fabric choices available. But how effective are they, especially at containing a sneeze? Now, researchers reporting in ACS Science and Engineering of Biomaterials used high-speed videos of a person sneezing to identify the optimal fabric mask design.
At the start of the pandemic, global shortages of surgical masks and N95 respirators led many people to make or purchase cloth masks. Now, with safe and effective COVID-19 vaccines available, mask restrictions are easing in many states. However, face masks will likely still be needed in some settings for some time, especially with the emergence of vaccine-resistant variants. They could also be useful in future pandemics. Face masks help reduce the spread of disease by blocking the tiny virus-laden droplets expelled from the nose and mouth when a person speaks, coughs or sneezes. A few studies have examined the effectiveness of various tissues at blocking machine-made droplets and aerosols, but so far none have been conducted under the explosive conditions of an actual human sneeze. Shovon Bhattacharjee, Raina MacIntyre and their colleagues at the University of New South Wales wanted to see how masks made of various fabrics and layers block respiratory droplets from a healthy adult’s sneezes.
The researchers made simple face masks from 17 commonly available fabrics. Each mask had one, two or three layers of the same or different fabrics. A healthy 30-year-old volunteer put on each mask, tickled the inside of his nose with tissue paper on a cotton swab, and then readjusted the mask just before a sneeze began. The researchers captured high-speed videos of sneezing and calculated the intensity of the droplets in the images in an area 2 cm from his mouth. With each layer of tissue, the blocking capacity of the droplets improved more than 20 times. Interestingly, all of the three-layer fabric combinations the researchers tested were more effective than a three-layer surgical mask. The best masks for blocking droplets contained a hydrophilic inner layer of cotton or linen, an absorbent midlayer of a cotton / polyester blend, and a hydrophobic outer layer of polyester or nylon. Machine washing of the masks did not decrease their performance; in fact, masks containing cotton or polyester performed slightly better after washing due to the shrinkage of the pores. Future studies are planned with more people and different age groups, the researchers said.
The authors acknowledge funding from the Australian Government’s National Board of Health and Medical Research and the University of New South Wales (UNSW) Scientia Ph.D. Scholarship.
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