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https://smart119.biz/ manga/000338.html

◆Theme
"How effective is a mouth shield, actually?"

Transparent masks are completely ineffective in preventing infections

◆Commentator
Taka-aki Nakada
CEO, Smart119 Inc.
Professor, Department of Emergency and Intensive Care Medicine, Chiba University Graduate School of Medicine
https://twitter.com/Nakada119

◆Point 1: Mouth shields are not effective in preventing infection
-Respiratory droplets will leak and spread if there is a gap between the face and the mouth
-Respiratory droplets can spread if there is a gap between the mask and the face

◆Point 2: Face masks cover the mouth and nose and are effective in preventing infection
-COVID-19 spreads from person to person by respiratory droplet infection
-The entry and exit points for airborne droplets are the mouth and nose
-In addition to coughing, sneezing, talking, and singing, droplets can be generated simply by breathing

◆Point 3: A well-fitted face mask is effective in preventing infection
-A mask that covers the mouth and nose without gaps will prevent from spreading droplets in and out
-The criteria of the best fit is that the edges (top and sides) of the face mask are in close contact with the face without creating any gaps

◆About face guards
-It covers the entire face but does not stick to the face and has many gaps
-In the medical field, it is recommended to use them in combination with face masks