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Knowledge

High-speed filming shows that a single sneeze spreads complex micro-droplets that can cloud an entire room.

Sneezing is a normal defence mechanism.

A forceful sneeze involves the coordinate contraction of many muscles to expel the air forcefully, along with mucus and saliva in the nasal passages. This produces a fine spray of particles that differ in size.

A team at MIT have been studying sneeze droplet dynamics for many years. They assumed that droplets leave the mouth fully formed, and that larger and heavier droplets would travel further.

It turns out that sneezing is much more complex.  High speed filming recorded sneeze droplets exiting the mouth and nose as a ‘high’ propulsion sneeze cloud’.

This showed the sneeze initially leaving the mouth as a sheet of liquid that then bursts into filaments before finally breaking apart into droplets.  These droplets only form when the sneeze cloud is clear from the body.

The size of the particles formed varies from person to person. It’s not just the force of the sneeze that dictates the size of the droplets, but also the complex make up of mucus and saliva in the ejected sneeze cloud.

Implications

This research highlights the wide variation of droplet sizes generated by sneezes. Some people studied were super-spreaders and within a few minutes the droplets had spread across an entire small room and reached the height of air ducts.

There was no simple relationship between the force of the sneeze and how far the droplets spread.

Limiting the spread of droplets is an important way to limit transmission because diseases such as the flu and measles are spread through droplets that are either transmitted by contact with surfaces or the air into the body.

So this year, make sure you cover your mouth and nose before you sneeze. If someone is sneezing around you, they could be a ‘super sneezer’ so take precautions.

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