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Covid-19 research shows downsides of face shields and valve masks
- US study finds the more comfortable alternatives give less protection than cloth and surgical coverings
- Chinese doctor agrees, and describes exhalation valves as ‘selfish’ because they only protect the wearer
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Face shields and masks with exhalation valves have become a popular alternative for people looking for protection against Covid-19, the disease caused by the new coronavirus, but American research has cast doubt on their effectiveness.
Researchers from Florida Atlantic University examined the performance of face shields and exhalation valves in impeding the spread of aerosol-sized droplets – one of the main forms of Covid-19 transmission – with disturbing results.
While clear plastic face shields blocked the initial forward motion of the jet of droplets, once expelled they were able to move around the visor relatively easily and spread out over a large area, according to the study published on September 1 in peer-reviewed scientific journal Physics of Fluids.
Visualisations for a mask equipped with an exhalation port indicated a large number of droplets passed through the valve unfiltered.

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Scientists said they did the research to help the public understand the effectiveness of face shields and masks equipped with exhalation valves, increasingly popular substitutes for regular cloth or surgical masks because people find them more comfortable.
Face shields reduce humidity and fogging when worn with glasses and are easier to breathe in. They also protect the eyes from splashes and sprays of infected droplets, are easily cleaned and disinfected, and allow visual communication for the hearing-impaired.
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