A muscle misfiring
What Causes Hiccups?
A hiccup is your breathing muscle jerking while the throat snaps shut on the incoming air.
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Step 1 of 5
A muscle under your lungs does your breathing.
The diaphragm pulls down to draw air in and relaxes to let it out. Normally it moves smoothly and you never notice.
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Step 2 of 5
A hiccup is that muscle jerking.
An irritated nerve makes it contract sharply and out of turn, pulling in a sudden unplanned gulp of air.
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Step 3 of 5
The sound comes from the throat.
About 35 milliseconds later the vocal cords snap shut on the incoming air. That abrupt stop makes the noise — not the muscle itself.
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Step 4 of 5
Almost anything can set it off.
Eating fast, fizzy drinks, a sudden temperature change or excitement all irritate the nerves running to the diaphragm.
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Step 5 of 5
The remedies all target the same nerves.
Holding your breath, drinking cold water and swallowing hard all change nerve signalling or carbon dioxide levels enough to break the cycle.
Babies hiccup in the womb, long before they breathe air. Nobody is quite sure what it is for.
The short version
A hiccup is the diaphragm jerking involuntarily while the vocal cords snap shut on the incoming air.
Try it yourself
Next time you hiccup, hold your breath and count to twenty. Rising carbon dioxide often stops the cycle.
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