Many people who don’t like face masks have opted for plastic face shields or masks with valves, making it easier to breathe.
But new research has found that these types of face coverings may not stop the spread of Covid-19 as effectively as regular cloth or disposable masks.
Droplets can escape masks with valves
Scientists in the US found that masks with an "exhalation port" can allow a large number of droplets to escape through the air valve unfiltered.
They warn this makes them ineffective at stopping the spread of Covid-19 if the person wearing the mask has the virus.
The study, named ‘Visualizing droplet dispersal for face shields and masks with exhalation valves’, was published in the Physics of Fluids journal.
In the study, researchers used a hollow manikin head and then simulated a cough or sneeze with a pressure impulse from a manual pump.
Tracers made from droplets of distilled water and glycerin were then expelled through the mouth opening.
The study’s abstract explains that masks “equipped with an exhalation port indicate that a large number of droplets pass through the exhale valve unfiltered, which significantly reduces its effectiveness as a means of source control.”
What about plastic face shields?
Researchers also tested clear plastic face shields and found them to be less effective than surgical or cloth masks.
Although it was found that a plastic face shield can block the initial forward motion of a simulated jet of a cough or a sneeze, the expelled droplets can then move around the visor with ease, allowing them to spread out over a large area.
The study goes on to highlight the best type of mask to wear.
It says: “Our observations suggest that to minimize the community spread of COVID-19, it may be preferable to use high quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves.”