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Why Do We Get Hiccups? Theories About Their Purpose in Babies and Adults

Category: The Body

Hiccups start with a sudden spasm of the diaphragm, the muscle between your chest and belly. Immediately after, the glottis in your throat snaps shut, making the "hic" sound [1]. From the contraction of the muscle to the closing of the glottis, it takes about 35 milliseconds, or 0.035 seconds [2]. It is strange because hiccups can start before a baby is even born. They are said to appear before the reflexes for swallowing or breathing [2]. If hiccups seem to have no use, why do they still happen? This article looks at three ideas researchers have proposed, along with how our brains react to them.

1. Why Do Hiccups Happen Before Birth?

Hiccups begin when the diaphragm contracts suddenly. Then, the vocal cords close quickly, creating the sound [1]. Common triggers include a full stomach, alcohol, or spicy food, but often the cause is unclear [1]. The mystery is that in fetuses, hiccups are said to occur before the reflexes to swallow or breathe appear [2]. If they are useless, why are they present so early in development?

2. Tadpole Breathing Theory: Are Hiccups a Leftover from Amphibians?

In 2003, researchers proposed that hiccups might be a leftover from how amphibians like tadpoles breathe [3]. Tadpoles use gills to take oxygen from water. The theory suggests that the nerve pattern for hiccups is similar to the pattern for gill breathing. Supporting this, hiccups involve closing the glottis while inhaling, develop early in life, and are suppressed by carbon dioxide [3]. Why would humans keep this? The same theory suggests the nerve circuit for hiccups may have helped build other circuits for breathing or sucking milk. So, it might not be useless, but a foundation for other important functions. However, this is just a hypothesis, not a proven fact.

3. Burp Reflex Theory: Do Hiccups Help Babies Release Air?

Another idea, proposed in 2012, is that hiccups are an evolved "burp reflex" to help babies release air from their stomachs [2]. Babies swallow air when they drink milk. A reflex to expel this air would be useful. According to this review, newborns spend up to 2.5% of their time hiccuping, which is about 36 minutes a day [2]. This theory and the tadpole theory are presented side-by-side in scientific reviews [2]. Neither is confirmed as the correct answer. Scientists still disagree on why hiccups happen. To understand more, we must look at what happens inside the baby's body.

4. How Hiccups May Help a Baby's Brain Learn

In 2019, a team at University College London studied 13 babies, including some born early and some born on time [4]. They found that every time the diaphragm spasmed during a hiccup, there was a large electrical response in the brain [4]. This means hiccups send strong signals to the brain. Researchers think this might help babies learn how to grasp the movement of their breathing muscles [4]. Since only 13 babies were studied, this is not yet proven. But it shows that hiccups are not just random spasms; they involve the brain. This leads to another question: if hiccups are linked to breathing control, can we stop them?

5. Does Holding Your Breath Really Stop Hiccups?

It is said that hiccups are suppressed when carbon dioxide levels in the blood rise [2]. Holding your breath increases carbon dioxide, which is why some people think it stops hiccups. This idea also connects to the tadpole theory, as gill breathing is also affected by carbon dioxide [3]. However, having a logical reason does not mean it always works. The MSD Manual states that home remedies like holding breath or drinking water quickly are not proven to be better than others [1]. Do not force yourself to hold your breath if it is uncomfortable. This article does not guarantee that any method will stop hiccups.

6. Does the FISST Straw Device Stop Hiccups?

In 2021, researchers reported a device called FISST, a tube that only releases water if you suck hard [5]. The explanation is that hard sucking contracts the diaphragm and closes the epiglottis, stimulating two nerves at once to stop the hiccup [6]. In an online survey of 249 people, about 92% said it stopped their hiccups [5]. However, there was no control group, and the results were self-reported. This is not proof of effectiveness yet. Randomized trials are needed. Most hiccups stop on their own. If they last more than 2 to 3 days, seeing a doctor is recommended [1].

7. What You Can Do When You Get Hiccups

If you get hiccups, do not try to force them to stop. Instead, count how many happen in one minute. Notice how your throat feels when the "hic" sound occurs. If you feel uncomfortable, tell an adult immediately. You can also look at diagrams of the diaphragm in library books about the human body. It is a dome-shaped muscle between the chest and belly. For official information, check the "Hiccups" page in the MSD Manual for causes and when to see a doctor [1].

Sources

  1. MSD Manual Home Edition "Hiccups" https://www.msdmanuals.com/ja-jp/home/03-消化器系の病気/消化器系の病気の症状/しゃっくり (Explains the mechanism, triggers, home remedies, and duration.)
  2. Howes D. (2012) Hiccups: A new explanation for the mysterious reflex. BioEssays https://pmc.ncbi.nlm.nih.gov/articles/PMC3504071 (Discusses the 35ms timing, fetal hiccups, the burp reflex theory, and carbon dioxide.)
  3. Straus C. et al. (2003) A phylogenetic hypothesis for the origin of hiccough. BioEssays https://dc2.philarchive.org/rec/STRAPH (Proposes the theory that hiccups are a remnant of amphibian gill breathing.)
  4. UCL News (2019) Newborn baby hiccups could be key to brain development. https://www.ucl.ac.uk/news/2019/nov/newborn-baby-hiccups-could-be-key-brain-development (Reports on electrical brain responses in newborns during hiccups.)
  5. JAMA Network Open (2021) FISST report. https://pmc.ncbi.nlm.nih.gov/articles/PMC8214157 (Details the survey of 249 people and the 92% success rate, noting limitations.)
  6. UT Health San Antonio news. https://news.uthscsa.edu/team-describes-science-based-hiccups-intervention/ (Explains the physiological mechanism of how the FISST device works.)
  7. Whitehead K. et al. (2019) Hiccups in newborn infants evoke cortical responses. Clinical Neurophysiology. https://www.sciencedirect.com/science/article/pii/S1388245719308588 (The original research paper on brain activity in 13 infants.)