Sneezing May be More Gross Than You Could Have Imagined

Sneezing may be more gross than you could have ever imagined. New, high-speed videos show that as a person sneezes, they launch a sheet of fluid that balloons, then breaks apart in long filaments that destabilize and finally disperse 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.

"It's important to understand how the process of fluid breakup, or fluid fragmentation, happens," said Lydia Bourouiba, one of the researchers, in a news release. "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?"

Understanding how sneezing disperses droplets can help researchers map the spread of infections through the environment, as well as identify individuals who may be "super spreaders."

"What we saw was surprising in many ways," said Bourouiba. "We expected to see droplets coming out fully formed from the respiratory tract. It turns out that's not the case at all. And this gives us a good baseline to expand our mechanistic understanding of violent expirations."

Currently, the researchers are setting up a new lab space at MIT specifically designed to accommodate parallel experiments to understand various modes of disease transmission. This space will also include a smaller, climate-controlled chamber in which they will be able to visualize sneezes, coughs and other modes of disease transmission, in collaboration with medical partners.

"The way transmission routes are being quantified even today still rely on the traditional way that has prevailed for hundreds of years, which is talking to people to survey who they talked to, where did they go, etcetera," said Bourouiba. "There are clear limits to the accuracy of the data acquired via this process, and we are trying to have more precise measures of contamination and ranges to root disease control and prevention strategies in the physical sciences."

The findings are published in the journal Experiments in Fluids.

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