Face masks work – as long as you don’t turn your head

TURNING your head to cough while wearing a face mask could make you more likely to infect someone, scientists have warned.

Jets of air can escape from the side and back of surgical masks, potentially allowing droplets from an infected person to come into contact with people near them, a study has found.

Scientists from the University of Edinburgh’s School of Engineering tested the effectiveness of seven types of face covering and found that they all could help limit the spread of Covid-19.

But while the forward distance of an exhaled breath is reduced by more than 90 per cent, sidewards “leakage” from the mask of a coronavirus-positive person could be a “major hazard”, explained Dr Ignazio Maria Viola, who coordinated the project.

Only masks that form a tight seal were found to prevent the escape of virus-laden fluid particles, it concluded.

Dr Felicity Mehendale, a surgeon at the University of Edinburgh’s Usher Institute, said: “It was reassuring to see the handmade mask worked just as well as the surgical mask to stop the wearer’s breath flowing directly forwards. This suggests some handmade masks can help to prevent infecting the public. But, the strong backward jets mean you need to think twice before turning your head if you cough while wearing a mask, and be careful if you stand behind or beside someone wearing a mask.”

However, Dr Antonio Lazzarino, from UCL’S Department of Epidemiology and Public Health, said it could not be concluded from this study that face coverings presented a major hazard.

“This study is meant to describe the physics of airflows with masks; it is not meant to experiment on the uses of masks to stop epidemics,” he said.

The team also discovered that a regular medical procedure known as extubation – the removal of a breathing tube used during anaesthesia and when patients are on a ventilator – may increase the risk of spreading Covid-19.

Simulations showed that the coughing that regularly accompanies extubation caused people nearby to be enveloped in the patients’ exhaled air, potentially putting clinicians and others at high risk of exposure to the virus.

‘The strong backward jets mean you need to think twice before turning your head if you cough’