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When chancellor of the exchequer Rishi Sunak was spotted buying lunch from Pret, all eyes were on him and his fetching grey mask.
The face covering fitted well to his face, covering his nose and mouth (top marks there), but it also featured a valve – and here lies the problem.
Valved face covers are banned in some cities and counties in the United States because they can expel the wearer’s germs into the environment.
People are told to wear face coverings to protect others. But when people wear face masks with valves, this doesn’t quite go to plan.
Making the most of @Pret's price cut in response to the VAT reduction that takes effect today for the tourism and hospitality sectors.— Rishi Sunak (@RishiSunak) July 15, 2020
As part of our #PlanForJobs this temporary cut will help over 150,000 businesses protect the jobs of 2.4 million people. pic.twitter.com/mSh6jOvBlp
Experts say the one-way valve closes when a person breathes in and opens when they breathe out. This means while the valve doesn’t let germs in, protecting the wearer, it does allow a person’s exhalations to leave the mask – and therefore does not protect others and slow the spread of the virus.
Professor Trisha Greenhalgh, an expert in primary care at University of Oxford, told HuffPost UK: “The valve acts like an exhaust pipe, potentially spewing germs out to the environment.
“Cloth face coverings are the best thing. They stop droplets – that’s why they get wet of course, and you have to change them when they do.
“Droplets contain viral particles so the more droplets get caught in your face covering, the fewer germs get into the air. A valved mask bypasses the barrier and potentially emits the droplets in an explosive gas cloud.”
The valve acts like an exhaust pipe, potentially spewing germs out to the environment. Professor Trisha Greenhalgh
Some people argue that valved masks can have filters between the mouth and the valve – therefore, isn’t the air people expelling going to be clean?
“It’s true that some masks have a valve that isn’t as dangerous as most valves, but it’s still a very dumb thing for a politician to wear a valved mask because it gives the message that valved masks, in general, are a good thing,” says Prof Greenhalgh. “They’re not, they’re a bad thing.”
A study published in the journal Infection Control and Hospital Epidemiology concluded that the use of masks with valves in the community “may be an additional and under-recognised transmission source” – and therefore they shouldn’t be used.
Earlier this month, Dr Bharat Pankhania, a senior clinical lecturer at the University of Exeter Medical School, urged people to stop wearing masks with valves in them. He told LBC they force a “high velocity flow of air from the mouth out through the valve which could create a plume of infection”.
“Wearers can propel, much further, the very droplets we are trying to capture within the mask,” he said.
Clear messaging on face masks is crucial for the adoption of wearing face masks and coverings by the general public, a study by the University of Oxford found. But so far, the messaging has been anything but.
On Tuesday, the 10 Downing Street Twitter account shared a public health video which showed an animated man wearing what appeared to be a face mask with a valve on it. HuffPost UK contacted 10 Downing Street for comment on this, but is yet to hear back.
This article originally appeared on HuffPost and has been updated.