Sneezing is your nose’s way of ejecting any irritants or foreign bodies that have snuck inside it; unfortunately, if you happen to be nearby anyone as you eject the sticky mass out of your nasal cavities, they may get infected with your germs. As it turns out, scientists know very little about how the ejected phlegm behaves as it rockets forwards. But a team of researchers from the Massachusetts Institute of Technology (MIT) has now mapped out the sequence of shifting shapes that form during sneezing, as reported by BBC News.
At a recent meeting of the American Physical Society’s Division of Fluid Dynamics in Boston, Dr Lydia Bourouiba announced that the morphology of the blobs of snot that are launched out of your nose is actually quite complex. This was revealed after using cameras to track how these pathogen-carrying clumps traveled through the air. Sneezing is a highly effective transmitter of diseases, after all – from the common cold virus to measles or SARS.
The clouds of sneeze droplets had been studied using a similar technique before, but the initial stage of sneezing and particle ejection was poorly described. “The part that is still a big unknown is: how are these drops actually formed and what is their size distribution? What I wanted to do was go upstream and look at the mouth, at what is coming out,” Bourouiba told BBC News.
For this new study, due to be published in the journal Experiments in Fluids, two healthy people were induced to sneeze through a little nasal tickling, and their nasal ejections were recorded in two-dimensions on a high-speed camera. They were prompted to sneeze about 50 times each day.
Initially, it was thought that the disintegration of the blobs of phlegm and saliva mostly occurred in the respiratory tract, but as their initial results showed, the break up continued long after the material rapidly exited the nose. Although the pattern and evolution of shapes vary, the generalized process involves a sheet of interconnected droplets turning into bag-shaped bursts, before ligaments stream off these shapes and destabilize into individual droplets.
Combining its experimental data with several computer simulations of sneezing, the team found that sneezes can spread material up to a distance of 7.9 meters (26 feet). Until now, most researchers assumed the larger droplets traveled farther, as they were likely to have more momentum. However, the reality is quite different: the smaller droplets are light enough to be suspended in the sneeze cloud, allowing them to stay airborne for longer than expected.
Image credit: After the initial jet of saliva and phlegm, a cloud of suspended droplets then drifts across the room, marked here by the change in the direction of travel. Bourouiba et al./MIT
Sneezing is, of course, highly variable: some attempt to capture their sneeze, some sneeze repeatedly, and others fire their droplets across the room. Nevertheless, this study is the first to accurately map the spread of a variety of sneezes across a room in such immaculate detail.