Why Do We Hiccup? What Causes Hiccups and What Actually Helps

In the middle of an important meeting, in a silent classroom or right after a meal — that uncontrollable “hic”. Hiccups are a reflex almost everyone knows but few of us think about. Scientists understand well how hiccups happen; why they exist is still up for debate.

The anatomy of a hiccup

The star of the show is the diaphragm, a large dome-shaped muscle that separates the chest from the abdomen. Each time we breathe in, it contracts and moves down, expanding the chest so air flows into the lungs.

During a hiccup this regular rhythm is disrupted, and two things happen in very quick succession:

1. The diaphragm contracts suddenly. This is a spasm beyond our control; the muscles between the ribs usually contract at the same moment.
2. Air rushes in. The sudden contraction starts a powerful flow of air towards the lungs.
3. The glottis snaps shut. About 35 milliseconds later, the gap between the vocal cords — the glottis — closes abruptly. The airflow stops and the closing vocal cords make the familiar “hic”.

Hiccups usually repeat between 4 and 60 times a minute, and each person has their own rhythm.

Who is in charge of the reflex?

Hiccups are controlled by a reflex circuit in the brainstem. It has three parts:

• Nerves carrying the signal: especially the vagus nerve and the phrenic nerve. The vagus carries information to the brain from the stomach, oesophagus and throat; the phrenic nerve controls the diaphragm.
• The centre: a “hiccup centre” in the brainstem linked to the regions that regulate breathing.
• The response: commands sent to the diaphragm and larynx.

Stimulating any point along this pathway can set off hiccups — which is why their triggers are so varied.

What triggers hiccups?

The most common causes of short bouts are:

• Eating too fast or too much: a suddenly stretched stomach stimulates the vagus nerve.
• Fizzy drinks: gas in the stomach causes the same stretching.
• Alcohol: it irritates the stomach and affects the nervous system.
• Sudden temperature changes: such as an icy drink straight after very hot soup.
• Swallowing air: chewing gum, smoking or talking while eating quickly.
• Excitement and stress: emotions can affect breathing rhythm.

Why do hiccups exist? Evolutionary theories

Whether hiccups are good for anything is one of science’s curious puzzles, because in adults they seem to have no obvious benefit. But there are clues.

A reflex from the womb

Hiccups appear very early in human development. Babies start hiccupping in the womb towards the end of the first trimester — before regular breathing movements begin. Newborns also hiccup far more often than adults.

Theory 1: clearing air from the stomach

According to a theory proposed by psychologist Daniel Howes in BioEssays in 2012, hiccups are an “air-removal” reflex that evolved in suckling young mammals. Babies swallow air along with milk. The sudden suction in the chest during a hiccup pulls the air bubble from the stomach into the oesophagus, and the burp that follows expels it, making room for more milk.

The theory tries to explain why hiccups seem to be found only in mammals and why they are so frequent in babies.

Theory 2: a trace of gill-breathing ancestors

Another view holds that hiccups are a remnant of an ancient nerve circuit resembling the movement tadpoles use to breathe through their gills. Tadpoles draw water into their mouths and close the glottis so the water goes over the gills rather than into the lungs — a movement strikingly similar to a hiccup.

Theory 3: helping the brain learn to breathe

Research with newborns at University College London showed that each hiccup triggers a distinct wave of electrical activity in the baby’s brain. The researchers suggest these responses may help the infant brain learn to monitor and control the breathing muscles.

None of these theories is settled. Hiccups may simply be a reflex that was once useful and has become unnecessary in adults.

How do you stop hiccups?

There are countless home remedies for hiccups. Most rely on interrupting the reflex circuit somehow. Scientific evidence is mostly limited, but it is possible to see why some might work:

A 2021 study tested a device that makes you drink water forcefully through a special narrow straw. The method stimulates the diaphragm through strong suction and the vagus nerve through swallowing at the same time. Most participants reported that it stopped their hiccups. However, the study had no control group, so the results need confirming by further research.

There is no reliable evidence that a sudden fright works. A shock disrupts your breathing rhythm, so it may occasionally seem to work by coincidence.

When to see a doctor

Almost all hiccups are harmless and pass on their own within minutes. You should see a doctor if:

• hiccups last more than 48 hours;
• they make eating, sleeping or breathing difficult;
• they come with chest pain, abdominal pain or vomiting.

Long-lasting hiccups can signal an underlying problem such as acid reflux, irritated nerves, kidney problems, certain medicines or disorders of the nervous system. In that case, treatment targets the underlying cause.

The record: 68 years of hiccups

The longest recorded bout belongs to American Charles Osborne, who started hiccupping in 1922 and stopped only in 1990 — about 68 years later. In that time he married, had children and tried to lead a normal life. Thankfully, cases like his are extremely rare.

In short

A hiccup is a reflex in which the diaphragm contracts involuntarily and the glottis then snaps shut. A stretched stomach, fizzy drinks, alcohol and excitement can trigger it. Its evolutionary purpose is still debated: it may help babies clear air from the stomach, or it may be a remnant of a very old nerve circuit. Most hiccups stop within minutes — but persistent hiccups are always worth checking with a doctor.