Although we all know that sneezes and coughs transmit infections, little research had been done to model how they work. To address this knowledge gap, Lydia Bourouiba and John Bush of MIT’s Applied Mathematics Lab used high speed cameras and fluid mechanics to reveal why we’ve grossly underestimated the role of gas clouds in these violent expirations.

A novel study by MIT researchers shows that coughs and sneezes have associated gas clouds that keep their potentially infectious droplets aloft over much greater distances than previously realized.

Using advanced image processing and physics algorithms, MIT scientists have analyzed hundreds of high-speed sequences of sneezes to obtain an accurate 3D model of fluid clouds and droplet trajectories with some frightening results.

They found that smaller droplets travel really far because the cloud keeps them afloat. It’s surprising how far they can go, they said, which makes sneezes particularly dangerous in hospitals and other public spaces.

“When you cough or sneeze, you see the droplets, or feel them if someone sneezes on you,” says John Bush, a professor of applied mathematics at MIT, and co-author of a new paper on the subject. “But you don’t see the cloud, the invisible gas phase. The influence of this gas cloud is to extend the range of the individual droplets, particularly the small ones.”

Smaller drops, longer distances

Indeed, the study finds, the smaller droplets that emerge in a cough or sneeze may travel five to 200 times further than they would if those droplets simply moved as groups of unconnected particles — which is what previous estimates had assumed. The tendency of these droplets to stay airborne, resuspended by gas clouds, means that ventilation systems may be more prone to transmitting potentially infectious particles than had been suspected.