Under your lungs is a big dome-shaped muscle, the diaphragm, that pulls down to breathe you in. A hiccup is that muscle twitching by accident: it yanks down and sucks in a sudden gulp of air. A split second later the flaps at the top of your windpipe snap shut on the rushing air, and that's the 'hic!'. Hold your breath in the simulator and watch CO₂ build up until the twitching calms down.
Most people think a hiccup is just a funny kind of breath. In fact it is two events bolted together: the diaphragm misfiring to yank in air, then the glottis slamming shut about 35 milliseconds later, which makes it an interruption, not a breath at all.
What's actually happening
Breathing is supposed to be the smoothest thing your body does — the diaphragm, a broad dome of muscle slung beneath your lungs, drops to pull air in and relaxes to let it out, on and on, all day, without a thought. A hiccup is that smooth machine briefly losing its grip. The diaphragm gives a single sharp, involuntary yank downward, far harder and faster than any normal breath, and a slug of air rushes in through your windpipe in a fraction of a second.
The sound is the punchline, and it comes from a door slamming. About 35 thousandths of a second after the spasm yanks the air in, the glottis, the gap between your vocal cords at the top of the windpipe, snaps shut on that fast-moving column of air. The sudden stop is the "hic". So a hiccup is really two events bolted together: a muscle misfiring, then a valve slamming on the result. That is why a hiccup feels like a jolt rather than a breath; it is an interruption, not a part of breathing at all.
Why we have hiccups at all is genuinely unsettled, and the best guesses point backward in time. One idea notes that the nerve path is suspiciously like the gill-clearing reflex of tadpoles and lungfish — animals that gulp, then seal the airway so water does not follow air into the lungs. We may be running a leftover version of that ancient gulp. Whatever the origin, the folk cures all converge on one trick: hold your breath, breathe into a bag, or sip slowly, and you let carbon dioxide build up in your blood. Rising CO₂ seems to quiet the misfiring reflex, which is why the oldest remedy in the book actually has a mechanism behind it.
Holding your breath cures hiccups for a real reason: rising blood CO₂ quiets the misfiring diaphragm reflex.
- 1Next time you hiccup, take a slow deep breath and hold it for as long as is comfortable — you are letting carbon dioxide rise in your blood.
- 2If that fails, sip cold water steadily without pausing, or breathe gently in and out of a small paper bag for a few breaths.
- 3Each trick nudges CO₂ up or distracts the reflex arc. Note which works for you — the same remedy rarely works for everyone, which is half the mystery.
Common questions
Holding your breath, breathing into a bag or sipping slowly all let carbon dioxide build up in your blood. Rising CO₂ seems to quiet the misfiring reflex, which is why the oldest folk remedy actually has a mechanism behind it.
It is genuinely unsettled, but the nerve path resembles the gill-clearing reflex of tadpoles and lungfish, which gulp then seal the airway. We may be running a leftover version of that ancient gulp.
Yes. Foetuses hiccup in the womb, sometimes for many minutes a day, which is part of why some scientists suspect hiccups are an ancient reflex left over from before we breathed air.