The ongoing mystery of hiccups

Sierra Pisenti knows hiccups.

She really, really wishes she didn’t. Hers are loud and painful, can last for hours, and have shown up more than a dozen times a month since she was a tiny baby. A bad bout feels like being punched in the chest. “It’s a nightmare,” says Pisenti, a stay-at-home mom from California.

Your hiccups probably aren’t as bad as Pisenti’s, but you likely recognize the dreaded sensation: a tightening in your chest, the characteristic “hic”—and the desperation to make them end. And you probably have the same question as her:

“How is it possible that there isn't a solution?”

Hiccups have roots deep in our evolutionary history. Yet after millions of years, tens of thousands of years of human problem-solving, and decades of modern medicine, their origin and purpose is still largely opaque.

“Things like this, that are considered obvious or very simple, are often overlooked by many doctors,” says Mark Fox, a gastroenterologist at University Hospital in Zurich, Switzerland. “Swallowing, eating, drinking, what happens in normal life—none of this stuff will kill you if it doesn’t work well. But it will ruin your life!”

Slowly, researchers are chipping away at two halves of the hiccups equation: first, why they exist in the first place. And second, how on Earth can we get rid of them? 

Do we hiccup because we were once fish?

Hiccups are a simple reflex, like jerking when a doctor taps your knee, and they are ubiquitous among mammals, from domestic dogs to horses to rabbits.

They’re controlled by a reflex "arc," which carries nerve signals from the diaphragm to the brain and back again, over and over. First, something triggers the diaphragm—the sheet of muscle at the base of your lungs—to contract. It moves downward as it flexes, making space for your lungs to expand, just like a normal in-breath. But in the middle of the breath, the reflex tells your epiglottis—the little flap at the top of your throat that keeps food out of your windpipe—to snap shut. That’s the “hic” noise, and the cycle repeats until something interrupts the arc.

The initial trigger often originates from the phrenic or vagus nerves, which developed in our water-dwelling, gill-breathing fish and amphibian ancestors. The common culprit is the phrenic nerve, a long, inefficiently shaped cord that winds down the chest to the diaphragm. Its first appeared in mammals’ fishy antecedents—but theirs was short. It went straight to the gills, right next to the brain, instead of the far-off diaphragm. In modern mammals, there’s altogether too much nerve to get tickled and triggered.

The hiccup itself might have been useful when fish evolved into amphibians that lived partly on land. They needed to switch breathing systems: gills underwater, lungs in air. The “hic” closing the ancestral epiglottis let them send water into their mouth and then to the gills without filling their lungs.

It’s a good reminder that evolution doesn’t make things perfect—it uses what it’s got at hand, says Howes.

Or maybe we hiccup because we were once babies

But given we no longer breathe underwater, why hasn’t the reflex disappeared?

Because there may be other advantages, says Dan Howes, an emergency doctor with a longstanding interest in hiccups at Queens University in Ontario, Canada. One thing (almost) all baby mammals do is suckle milk. Babies hiccup much more often than adults. As they drink milk, they also suck in extra air; maybe, Howes suggests, hiccups help clear that air from the stomach reflexively—like a self-initiated burp.

There’s some evidence that after burping, babies can take in up to 20 or 30 percent more milk, a meaningful bump in calories and “a fairly significant survival advantage,” he says.

It's not just young infants who hiccup often (up to one percent of the whole day): Fetuses as young as 10 weeks old do, too. And they’re obviously not suckling yet.

Kimberley Whitehead, a researcher at University College London, hypothesized hiccups might help train fetuses’ brains to map out their internal body. “A baby needs to learn ‘Where is my diaphragm; where is this place I can exert control over my breathing,’” she says. Hiccups might help them “practice” breathing so they’re ready to hit the ground running when they’re born.

In one of her studies, she hooked up a suite of babies, some premature and some up to a few months old, to EEG electrodes and watched their brains as they experienced bouts of hiccups. The part of the cortex associated with the thoracic cavity—the central part of the body where our lungs and diaphragm sit—lit up during hiccups. That signaled that the hiccups were triggering activity in the brain, helping babies “map” those muscles onto the brain.

Can someone please just help me get rid of these hiccups already?

About 4,000 people come into U.S. hospitals yearly looking for help with the mostly benign ailment, but everyone deals with them: they’re routinely one of Google’s most searched health questions.

Most cases resolve independently within two days. Longer bouts can be a sign of an underlying problem, such as a brain tumor. Longer-persisting, continuous “intractable hiccups” are also common side effects of chemotherapy treatment or steroids; more than 90 percent of cases occur in men over 50. In intractable cases, the best treatment is dealing with the underlying condition.

Doctors have tested a suite of drugs to address hiccups: some relax muscles, possibly calming a spasming diaphragm, or change the reactivity of nerves. But there’s “a lack of good quality evidence to recommend specific treatment,” neuroscientists from Loyola University in Chicago wrote in a 2018 study.

A Japanese research group uses another strategy: making people breathe in high-concentration CO₂. “Put simply, a level of CO₂ retention in the body tricks the brain into thinking it has a life-threatening emergency and makes it forget about the hiccups,” writes Toshiro Obuchi, a thoracic surgeon and hiccups expert at St. Mary’s Hospital in Japan.

But if you can’t fly to Japan to have Dr. Obuchi treat you, those old wives’ tales—like drinking a whole glass of water in one gulp to standing on your head to getting really scared—can actually work, because they share a key principle: interrupting the reflex arc so that nerves and muscles are distracted by something else, says Ali Seifi, a neurointensivist at the University of Texas, San Antonio who became obsessed with finding a cure after seeing a patient wake up with inexplicable hiccups after brain surgery.

Drinking a glass of water in one go, for example, forces your diaphragm muscle to keep creating suction continuously, which occupies the phrenic nerve, interrupting one part of the reflex. A scare forces the vagus nerve, which controls calming responses, into action, interrupting the other part of the reflex.

But Seifi has designed a more consistent tool: a straw called the Hiccaway that forces the drinker to suck very hard—like drinking a thick milkshake. He hypothesizes that the effort engages both nerves, killing their ability to keep hiccups going.

Pisenti, like many long-term hiccup sufferers, hasn't ever been diagnosed with intractable hiccups; medicine doesn't always take the malady seriously. So finding the straw was a revelation. She reaches for it at the first glimmer of hiccups, and while it doesn’t get rid of them forever, it forces them into temporary submission. “It’s a life-changer,” she says.