Tiny droplets linger in the air for minutes in the aftermath of swirling tornadoes of fragmented mucus. This is the latest portrait painted by a team of MIT researchers who use high-speed imaging to study the fluid dynamics of sneezes, with the ever-clearer picture of these infectious sprays revealing more about the role they play in spreading disease.
For almost a decade, the Borouiba research group at MIT has sought to better understand the fluid dynamics of disease transmission, and in the last few years this has led them to uncover some intriguing mechanical workings of our sneezes. In 2014, the team discovered that sneezes set invisible gas clouds in motion that stealthily carry small droplets up to 200 times farther than previously thought.
Earlier this year, the researchers ran an experiment that placed human subjects against a black backdrop, among other settings. They set up a pair of high-speed monochrome cameras and focused on the mouths of the subjects, before tickling their noses to trigger the fiery nose explosions.
They found that, rather than the common perception of sneezes as a neat spray of uniform droplets, the event first launches a wide sheet of fluid into the air that then balloons and bursts into thin filaments. Only after that, are individual droplets formed that either fall to the ground or gather into the aforementioned floating gas clouds.
Led by Professor Lydia Borouiba, the team continues to probe sneeze clouds for clues on disease transmission. Borouiba tells us that they used high-speed cameras and various optical techniques for their latest experiment, which featured several volunteers who agreed to fire off a few nasal rockets in the name of science. And the new captures have revealed a few new tidbits about the composition of a sneeze, suggesting they are more complex than we might have thought.
The researchers say they feature many different kinds of movements, among which are swirls and vortexes. There is also a wider range of droplet sizes than expected, ranging from some relatively large ones to some very small. And the environment in which your sneeze is unleashed can have a big influence on the shape it takes, with air movement, humidity and temperature all factors in its size, form and duration.
But the researchers were most surprised by the discovery that under the right conditions, the tiniest droplets can remain airborne for several minutes while at the same time drifting several feet. They say that this means a single sneeze in a room could potentially infect every person in that room.
The end game here is to learn more about how sneezes behave so that action can be taken to reduce the risks of disease transmission in places like hospitals. As the researchers work towards this goal, they recommend sneezing into your elbow rather than your hands, something we're sure you'll agree to do after watching the slo-mo sneeze video above.
The research was published in The New England Journal of Medicine.
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