• Image by Allan Foster / CC BY-NC-ND (Flickr)
High-speed imaging of sneezes reveals a disgusting sight - but how best to prevent the droplets from going everywhere?
By
Signe Dean

15 Feb 2016 - 3:56 PM  UPDATED 21 Jun 2016 - 10:37 AM

It’s worse than we thought. When you sneeze, you don’t just produce a spray mist of potentially infectious saliva droplets. Instead, you launch a wide sheet of fluid that starts off ballooning, then bursts like a bubble, and finally disperses into a spray - much like the dynamics of tossing paint into the air.

Researchers at MIT captured over 100 high-speed videos of people sneezing to determine this pattern, and published their results last week in the peer-reviewed journal Experiments in Fluids.

“It’s important to understand how the process of fluid breakup, or fluid fragmentation, happens,” says lead author of the study, Lydia Bourouiba. “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?”

Top and side views of the rapid fragmentation process of mucosalivary fluid occurring during a healthy sneeze, captured at 6,000 to 8,000 frames per second. Image from “Visualization of sneeze ejecta: steps of fluid fragmentation leading to respiratory droplets.”

Scientists at MIT's Fluid Dynamics of Disease Transmission Laboratory hope that understanding the dynamics of infectious droplets can help map infections as they spread through the environment.

Back in 2014 these MIT researchers also demonstrated that coughs and sneezes produce not just infectious droplets, but whole clouds of gas. These sneeze clouds can travel from five to 200 times farther than they would have if the droplets were simply a disconnected group.

As these gas clouds are highly capable of remaining airborne, it means there’s high potential for indoor ventilation systems to spread the disease.

Do cover up, please

All this disgusting footage means that covering your mouth as you sneeze is vital for limiting the spread of nasties - but which is the best way to do it?

Most people instinctively just use their hands, which is a terrible idea. All that fluid - a nice mixture of saliva, mucus, and germs - ends up on your hands, and will transfer to the next surface you touch, where it can live for at least a few hours. Furthermore, the hands usually don’t cover all of the droplet cloud, and the potential for spreading disease is still high.

NSW Ministry of Health advises that you should use a tissue to cover your nose and mouth when coughing or sneezing - and importantly, throw that tissue out afterwards. This advice is echoed by health departments worldwide. If you don’t have a tissue or paper towel handy, it’s best to sneeze into the crook of your elbow.

According to a non-scientific test done by Mythbusters back in 2010, sneezing into your elbow can effectively prevent the fluids from spreading, whereas you could still sneeze through a tissue or hanky and end up with gunk all over your hands.

So, whatever you do, cover up that sneeze. And it remains crucial to wash your hands afterwards - and maybe wash your shirt if you have a cold and sneeze a whole bunch into your elbow.

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