These high-speed images of sneezes will make you never want to leave the house without a pack of tissues again. In the journal Experiments in Fluids, a group of MIT scientists who study the ways infections spread through snot sprays report that sneezes aren’t as simple as we thought. Rather, mucus ejects from our mouths and noses in “a complex cascade of events from sheets, to bag bursts, to ligaments, which finally break into droplets,” they write.
The researchers recorded the sneezes of three people using two high-speed cameras (6000 to 8000 frames per second). They tickled the subjects' noses, then took images of 100 sneezes.
They found that the droplets of saliva and mucus don’t spray ready-made from our bodies. Instead, the liquid emerges from your face in thick sheets that expand with your breath—kind of like your sneeze is blowing up a snot balloon. From there, the mucus-saliva mixture goes through a quick succession of shapes, becoming long, thin filaments before forming airborne droplets. Bigger droplets fall to the ground, while the smaller droplets remain suspended in a “turbulent cloud” of potentially infectious snot.
“We expected to see droplets coming out fully formed from the respiratory tract,” one of the study’s authors, MIT assistant professor Lydia Bourouiba, explains in a press release. "It turns out that’s not the case at all.” To their surprise, snot droplets aren’t uniform.
And some people spray differently than others. People with more elastic snot shot liquid filaments farther into the air than other sneezers, whose snot broke into droplets earlier. This might mean that some people are more likely to spread germs than others through their sneezes.
Bourouiba is creating a new lab to study the way infectious diseases spread through droplets, especially the common cold and the flu. In addition to studying how diseases spread through the environment, she also hopes to be able to identify people who are “super spreaders.” She has previously studied how coughs spread infectious drops through the air.
All images from the paper, “Visualization of sneeze ejecta: steps of fluid fragmentation leading to respiratory droplets,” by B. E. Scharfman, A. H. Techet, J. W. M. Bush, L. Bourouiba.