The scientists in Scotland hoping to discover whether masks help prevent spread of coronavirus or do more harm than good

In these worrying times, violently coughing while not covering your mouth is a definite no-no.

Yet in Dr Ignazio Maria Viola’s lab at the University of Edinburgh, Lucas is sitting in the corner doing exactly that.

Fortunately for us all, Lucas is a mannequin on loan from the medical school, who has been re-engineered to test the effectiveness of face masks in preventing the spread of viruses.

The Health Secretary Matt Hancock has said it enough times - the government's decision-making on Covid-19 will be “led by the science”. But when it comes to masks, it seems their suggestion that face coverings could have benefits is based more on common sense than cold hard data.

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As Dr Viola is at pains to point out, the data on masks isn’t simple.

Lucas breathes out compressed air through a mesh producing droplets of water to mimic the process of coughing.

As Dr Viola explains, given the threat of Covid-19, it’s not possible to use real human volunteers for the research.

They’re using imaging technology typically used to study air flow inside car engines or over aircrafts’ wings to look at how far and how fast air moves out of people’s mouths with and without a mask on.

What their cameras show is that talking - even heavy breathing - can send a jet of air containing potentially infectious particles, at least two metres from our mouths. At that point air flow is too faint to see if it's moving any further.

They’ve found masks definitely work, reducing the flow of air in one direction by at least 90%.

The team has tested nine different types of mask.

Clinical-grade masks that are designed to be fitted to the face are best at preventing jets of potentially infectious air.

But some homemade masks and poorly fitted clinical masks simply redirect the flow of air in different directions. Which means working next to someone in the wrong kind of mask might be worse than working next to them not wearing one.

What’s more, while a mask disrupts, or, in some cases, filters the flow of air, it can’t stop it.

“The total amount of air you breath out remains unchanged whether you’re wearing a mask or not,” says Dr Viola. “All the mask does is change the way the air flows.”

But it’s still not clear which size of particle from our cough, sneeze, or breath is most important for carrying the virus from one person to the next. So it’s not yet possible to say what kind of mask might be of most benefit in all situations.

If the virus is spreading via droplets, face covering should work pretty well. But if it’s genuinely airborne there are almost no masks that can stop a virus 100 nanometres across.

What’s more if people touch their face coverings - which are known to absorb moisture and therefore any viruses - they could actually amplify the spread of virus from hands.

Worse still, if people see face covering as an alternative to social distancing or deplete supplies of masks needed by frontline workers.

Adopting them widely could do more harm than good.