A sudden gale, from inside
Why Do You Cough?
A cough is a pressure explosion: seal the airway, squeeze hard, then let go all at once.
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Step 1 of 5
Your airway is lined with sensors.
Nerve endings all the way down the windpipe fire at dust, smoke, food that went the wrong way, or the mucus of an infection. Any of them can trigger a cough.
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Step 2 of 5
The first move is to shut the door.
Your vocal cords slam together and seal the airway. Nothing can move in or out, which is what makes the next step possible.
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Step 3 of 5
Then the pressure is built up behind it.
Your diaphragm and the muscles between your ribs push hard against the closed seal, raising the pressure in your chest far above the air outside.
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Step 4 of 5
Opening the seal releases it all at once.
The cords fly apart and the stored pressure escapes through a narrowed windpipe. The air leaves at up to 80 kilometres an hour, scraping the walls as it goes.
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Step 5 of 5
Suppressing one is why illness spreads.
The same blast that clears your airway sprays droplets several metres. That is the cough doing its job for you and against everyone nearby.
The noise is not the air. It is the walls of the windpipe and the vocal cords vibrating as the blast tears past them.
The short version
A cough seals the airway, builds up pressure behind it, and releases it in a blast fast enough to scrape the tube clear.
Try it yourself
Try to cough with your mouth wide open and your throat relaxed. You cannot — without the seal there is no pressure to release.
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