What causes hiccups?
You get hiccups when your diaphragm suddenly contracts on its own and your glottis snaps shut about 35 milliseconds later: that is what makes the “hic” (Howes, 2012). The reflex often starts with an overfull stomach and runs through the vagus and phrenic nerves.
Simplified diagram, not to scale. Dotted curves are estimates based on published timings and frequencies; the percentages in the notes are measured.
What causes hiccups?
The torso seen from the front, greatly simplified. Choose a situation, then tap a label on the drawing to learn what it is.
Sources: reflex, nerves, 35 ms delay, 4 to 60 hics a minute and effect of CO2 (Howes, BioEssays, 2012); length and frequency of bouts (Alvarez et al., JAMA Netw Open, 2021); fetus (Pillai and James, Arch Dis Child, 1990); babies (Brouillette et al., J Pediatr, 1980; Whitehead et al., Clin Neurophysiol, 2019); tricks (NHS, 2023). Drawing not to scale; the hic is shown in slow motion.
Keyboard: 1 to 3 situations, Space pause, L slow motion, R restart, ← → previous or next step.
Frequently asked questions about hiccups
How do you stop hiccups?
No method is well proven to stop hiccups, but most of the time they stop on their own within a few minutes (NHS; Moretto, 2013). The most common tricks are holding your breath, breathing into a paper bag, sipping ice-cold water, swallowing a little sugar or biting into a lemon (NHS). Holding your breath raises carbon dioxide, and breathing air richer in carbon dioxide reduces hiccups (Howes, 2012). A tool that makes you suck hard and then swallow stopped them in nearly 92% of cases according to 249 users, but the study had no comparison group (Alvarez, 2021).
How long does a bout of hiccups last?
A bout of hiccups usually lasts a few minutes: among 249 people surveyed, 65.9% had bouts shorter than 2 hours (Alvarez, 2021). In the same survey, 5.4% had already had a bout lasting 48 hours or more. Doctors call hiccups persistent after 48 hours, and intractable after one month (Moretto, 2013).
Why do hiccups make a “hic” sound?
The “hic” sound comes from the glottis, the opening between the vocal cords, which snaps shut about 35 milliseconds after the diaphragm contracts (Howes, 2012). The diaphragm starts to pull air in, then the glottis stops it dead: that jolt is what you hear. Hiccups come back 4 to 60 times a minute (Howes, 2012).
Are hiccups normal in babies?
Yes, hiccups are very common and normal in babies: in 20 newborns, they took up 2.5% of the time, in bouts lasting 8.4 minutes on average (Brouillette, 1980). They even start before birth, from about 9 weeks of pregnancy (Whitehead, 2019), and they are the fetus’s most frequent diaphragm movement before 26 weeks (Pillai, 1990). One unproven idea is that they help the baby’s brain learn to sense its own breathing (Whitehead, 2019). If your baby seems to have trouble feeding or breathing, it is best to talk to a doctor.
When should you see a doctor about hiccups?
See a doctor if hiccups last more than 48 hours, come back very often, stop you from eating, drinking or sleeping, or come with pain or trouble swallowing or breathing (NHS). Hiccups that last that long can be a sign of another condition, such as reflux, a side effect of some medicines or a nervous system disorder (Steger, 2015). The doctor then looks for the cause, rather than treating the hiccups alone.
True or false?
Holding your breath can calm hiccups.
True. Holding your breath raises carbon dioxide in the blood, and breathing air richer in carbon dioxide reduces hiccups (Howes, 2012). But this trick has never been compared in a proper trial, and no method is well proven (Moretto, 2013).
Hiccups only start after birth.
False. Hiccups appear from about 9 weeks of pregnancy (Whitehead, 2019). Before 26 weeks, they are even the fetus’s most frequent diaphragm movement (Pillai, 1990).
Hiccups lasting more than 48 hours are never a concern.
False. After 48 hours, hiccups are called persistent: they can be a sign of another condition and deserve medical advice (Moretto, 2013; NHS).
This page as text
The same information as the charts, to read without animation: for each chart, the values at the main moments, then the notes with their level of evidence.
What happens during a single hiccup?
The diaphragm jerks, air rushes in, then the glottis shuts about 35 milliseconds later: that is the “hic”. Only this delay is measured; the curves are estimates.
| Milliseconds, weeks of pregnancy or minutes | Diaphragm contraction (dotted) | Air coming in (dotted) | Glottis closed (dotted) | What happens |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | The start of the hiccup |
| 100 ms | 89 | 0 | 100 | after the start of the hiccup |
| 200 ms | 47 | 0 | 100 | after the start of the hiccup |
| 300 ms | 14 | 0 | 40 | after the start of the hiccup |
| 400 ms | 3 | 0 | 0 | after the start of the hiccup |
| 500 ms | 0 | 0 | 0 | after the start of the hiccup |
Key points
- The diaphragm suddenly contracts (Until 40 ms, Shown in humans)
A hiccup is a sudden, involuntary contraction of the diaphragm, often with the muscles between the ribs. Air is pulled quickly toward the lungs. Source: Howes, "Hiccups: a new explanation for the mysterious reflex", BioEssays, 2012 - The glottis shuts 35 milliseconds later (From 25 to 150 ms, Shown in humans)
About 35 milliseconds after the contraction starts, the glottis, the opening between the vocal cords, snaps shut. The incoming air is stopped: that jolt makes the “hic”. Source: Howes, "Hiccups: a new explanation for the mysterious reflex", BioEssays, 2012 - A reflex with one center and two nerves (Throughout the hiccup, Shown in humans)
The signal travels up the vagus nerve, the phrenic nerve and nerves of the chest, passes through a center in the brainstem, then comes back down to the diaphragm, the muscles between the ribs and the glottis. Source: Howes, "Hiccups: a new explanation for the mysterious reflex", BioEssays, 2012 - Often just one side (Throughout the hiccup, Shown in humans)
Most often, it is mainly the left half of the diaphragm that contracts. Source: Howes, "Hiccups: a new explanation for the mysterious reflex", BioEssays, 2012 - What is it for? (Throughout the hiccup, Hypothesis)
Hiccups do not help you breathe: the glottis shuts too early. One idea: they may have evolved to push swallowed air out of the stomach, which would help small nursing mammals drink more milk. Source: Howes, "Hiccups: a new explanation for the mysterious reflex", BioEssays, 2012 - Estimated curves (Throughout the hiccup, Hypothesis)
Only the 35-millisecond delay between the contraction and the closing of the glottis is measured. The shape and length of the curves are estimates.
Why do babies get hiccups so often?
Hiccups start before birth, around 9 weeks of pregnancy, and stay common in newborns: about 2.5% of their time. Percentages measured; curves estimated.
| Milliseconds, weeks of pregnancy or minutes | Hiccups (dotted) | Breathing movements (dotted) | What happens |
|---|---|---|---|
| 8 wk | 0 | 0 | 8 weeks of pregnancy |
| 16 wk | 92 | 14 | 16 weeks of pregnancy |
| 24 wk | 88 | 27 | 24 weeks of pregnancy |
| 32 wk | 38 | 88 | 32 weeks of pregnancy |
| Birth | 30 | 100 | (40 weeks) |
| +8 wk | 22 | 100 | 8 weeks after birth |
| +16 wk | 15 | 100 | 16 weeks after birth |
Key points
- From 9 weeks of pregnancy (Until 16 weeks of pregnancy, Shown in humans)
The fetus gets hiccups very early, from about 9 weeks, before it has regular breathing movements. Source: Whitehead et al., "Event-related potentials following contraction of respiratory muscles in pre-term and full-term infants", Clin Neurophysiol, 2019 - The most frequent movement before 26 weeks (Until 27 weeks of pregnancy, Shown in humans)
In 45 fetuses followed by ultrasound, hiccups were the most frequent diaphragm movement before 26 weeks. They dropped sharply around 24 to 26 weeks, then breathing movements increased, especially from 26 to 32 weeks. Source: Pillai and James, "Hiccups and breathing in human fetuses", Arch Dis Child, 1990 - About 1% of the day (From 30 weeks of pregnancy to 2 weeks after birth, Shown in humans)
In 13 babies born between 30 and 42 weeks, hiccups took up about 1% of the time, in episodes of about 8 minutes. The brain responded to each hiccup. Source: Whitehead et al., "Event-related potentials following contraction of respiratory muscles in pre-term and full-term infants", Clin Neurophysiol, 2019 - Newborns: 2.5% of the time (From birth, Shown in humans)
In 20 babies, hiccup episodes lasted 8.4 minutes on average and took up 2.5% of the time. Source: Brouillette et al., "Hiccups in infants: characteristics and effects on ventilation", J Pediatr, 1980 - What are a baby’s hiccups for? (Throughout, Hypothesis)
Two unproven ideas: each hiccup may help the brain learn to sense the breathing muscles (Whitehead, 2019); or it may be a reflex that helps push out air swallowed while nursing (Howes, 2012). Source: Whitehead et al., "Event-related potentials following contraction of respiratory muscles in pre-term and full-term infants", Clin Neurophysiol, 2019 - Estimated curves (Throughout, Hypothesis)
The percentages in the notes are measured; the shape of the curves links these measurements and remains an estimate.
How long do hiccups last, and what stops them?
Most bouts last less than 2 hours and stop on their own. The well-known tricks have barely been tested. Estimated curves.
| Milliseconds, weeks of pregnancy or minutes | Hiccups per minute, doing nothing (dotted) | Hiccups per minute, if a trick works (dotted) | What happens |
|---|---|---|---|
| Start | 70 | 70 | The start of the bout |
| 20 min | 65 | 0 | after the start of the bout |
| 40 min | 43 | 0 | after the start of the bout |
| 60 min | 24 | 0 | after the start of the bout |
| 80 min | 10 | 0 | after the start of the bout |
| 100 min | 4 | 0 | after the start of the bout |
| 120 min | 2 | 0 | after the start of the bout |
Key points
- 4 to 60 hiccups per minute (Until 20 min, Shown in humans)
During a bout, hiccups come back at a fairly steady pace, 4 to 60 per minute depending on the person. Source: Howes, "Hiccups: a new explanation for the mysterious reflex", BioEssays, 2012 - Usually less than 2 hours (Throughout the bout, Shown in humans)
Among 249 people, 65.9% usually had bouts shorter than 2 hours. Only 5.4% had ever had a bout of 48 hours or more. Source: Alvarez et al., "Evaluation of the Forced Inspiratory Suction and Swallow Tool to Stop Hiccups", JAMA Netw Open, 2021 - CO2 slows hiccups down (Until 30 min, Shown in humans)
Breathing air richer in carbon dioxide (CO2) reduces hiccups. Holding your breath or breathing into a paper bag are based on this idea. Source: Howes, "Hiccups: a new explanation for the mysterious reflex", BioEssays, 2012 - Suck hard, then swallow (From 5 to 20 min, Shown in humans)
A tool that makes you suck hard before swallowing stopped hiccups in nearly 92% of cases, according to 249 users. But the study had no comparison group and the tool’s inventor was one of the authors. Source: Alvarez et al., "Evaluation of the Forced Inspiratory Suction and Swallow Tool to Stop Hiccups", JAMA Netw Open, 2021 - Old home remedies (Throughout the bout, Hypothesis)
Ice water, sugar, holding your breath, knees to chest: they may help, without solid proof. They stimulate the throat or the vagus nerve, or raise CO2. Source: NHS, "Hiccups", 2023 - More than 48 hours: see a doctor (After 60 min, Shown in humans)
After 48 hours, hiccups are called persistent. They can reveal another condition: the doctor looks for the cause. Prescription medicines exist, but trials are few. Source: Steger, Schneemann and Fox, "Systemic review: the pathogenesis and pharmacological treatment of hiccups", Aliment Pharmacol Ther, 2015 - Estimated curves (Throughout the bout, Hypothesis)
Only the numbers in the notes are measured; both curves are estimates, on a relative scale.
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