「くしゃみは時速160km」は盛りすぎ？ 実測で分かった本当の速さと、止められない理由

Some books say a sneeze travels at over 160 kilometers per hour. But scientists who measured the air from real sneezes found much slower speeds. In one study, the fastest air they could see moved at about 16 kilometers per hour, like a bicycle.

However, small drops from a sneeze can ride in a cloud of warm air and go several meters. So please cover your mouth when you sneeze.

You may have heard that a sneeze shoots out air at more than 160 kilometers per hour. However, measurements of the air do not support this claim. In 2013, researchers filmed six people sneezing with a special camera that shows air movement. The fastest speed they could see was about 4.5 meters per second, or about 16 kilometers per hour. Other estimates for the air are higher, but none reach 160.

On the other hand, a 2014 study at MIT found that tiny droplets travel inside a warm, moist cloud of breath, so they can spread several meters. A sneeze is a reflex controlled by the brain, so it is very hard to stop once it starts.

You will often hear that a sneeze leaves the nose at over 160 kilometers per hour. Photos from the 1940s did show droplets flying at up to 46 meters per second, but droplets and air do not always move at the same speed.

Air is invisible, so researchers film sneezes with imaging techniques that reveal differences in air temperature and density. In a 2013 study, a team recorded six volunteers and estimated a maximum visible speed of about 4.5 meters per second, roughly 16 kilometers per hour. That may be too low.

MIT researcher Bourouiba has suggested that exhaled air can reach 10 to 30 meters per second. Even that is well below the popular figure. Distance matters more than speed. In 2014, Bourouiba and colleagues showed that small droplets ride inside a warm, moist cloud of exhaled gas.

The cloud carries them much farther than single droplets could travel, sometimes several meters. A sneeze is also a reflex controlled by the brainstem, so it is hard to stop. Holding one in by blocking both nose and mouth is a bad idea. In one rare case from 2018, it tore a man's throat.