ANATOMY OF A SNEEZE

Reader's Digest Asia Pacific - - Contents - BRAN­DON SPECKTOR

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.

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