Sneezes, Frame by Frame

Here’s some incentive to cover your mouth the next time you sneeze: New high-speed videos captured by MIT researchers show that as a person sneezes, they launch a sheet of fluid that balloons, then breaks apart in long filaments that destabilize, and finally disperses as a spray of droplets, similar to paint that is flung through the air.

Using two high-speed cameras, the researchers recorded more than 100 sneezes from healthy human subjects and captured the fraction of a second during which fluid is expelled from the mouth and flung through the air. Almost every sneeze produced the same paint-like pattern of fluid fragmentation, with slight variations: The more elastic the fluid, or saliva, the longer the fluid traveled before breaking into droplets.

This complex pattern of fluid breakup runs counter to what most people expect, which is that a sneeze produces a simple and uniform spray of droplets.

“It’s important to understand how the process of fluid breakup, or fluid fragmentation, happens,” said Lydia Bourouiba, the Esther and Harold E. Edgerton Assistant Professor in the Department of Civil and Environmental Engineering and head of the Fluid Dynamics of Disease Transmission Laboratory at MIT. “What is the physics of the breakup telling us in terms of droplet size distribution, and the resulting prediction of the downstream range of contamination?”