ANATOMY OF A SNEEZE

A-choo! The distance those nasty germs can travel is nothing to sneeze at.

Simultaneously expressing itself as a solid, a liquid and a gas, the common sneeze is one of nature’s grossest miracles. Researcher Lydia Bourouiba has a different name for sneezes, though: violent expiratory events. That’s also the title of a recent study in which her team analysed sneezes, millisecond by millisecond, with a high-speed camera and sophisticated computer models. What did they find? There’s more to a sneeze than what you see in your hanky – and that could influence our understanding of the way diseases spread. Here’s a closer look at what scientists see when you say achoo!

1 Like a blast of birdshot, the initial ‘jet phase’ of a sneeze lasts only milliseconds but can send an estimated 40,000 droplets of various sizes scattering outward as fast as a car on a highway.

2 The largest droplets (illustrated in green) rocket out of the sneezer’s mouth and rapidly plummet under their own weight within a few seconds. Average distance travelled: one to two metres.

3 In the ‘puff phase’ of a sneeze (illustrated in red), a turbulent cloud of warm, moist air swirls through the air, carrying the sneeze droplets with it.

4 The cloud grows and slows as it pulls in air from the environment, carrying the smallest droplets up to eight metres from their point of origin.

5 Buoyed by the cloud, small droplets can easily stay airborne long enough to reach overhead vents (and thus anywhere in a building). It’s a big problem. But there’s a solution an arm’s length away: cover sneezes with a sleeve or tissue, wash your hands regularly, and keep those germs to yourself.