Why do we hiccup, sneeze and yawn? A hiccup makes a quick "hic" sound, a sneeze is a sudden burst of air that rushes out of your nose and mouth, and a yawn is a deep breath in with the mouth wide open, often with the eyes closing and a stretch of the body. Most people get hiccups sometimes, and they go away by themselves in a few minutes. A sneeze is a reflex, which means your body does it on its own: you cannot decide when it happens.

A sneeze starts when something irritates the lining of the nose or throat, and sensory nerves send the alarm. Nerves in the nose send a message to the brainstem, and many muscles then work together to push the air out. In the sneeze reflex, a control area in the medulla at the back of the brain, the sneeze-evoking zone, is the main central hub for signals coming from the trigeminal nerve. A cough and a sneeze are different reflexes: the cough reflex starts in the larynx and lower airways and uses the vagus nerve, while a sneeze starts in the nose, where irritants stimulate the trigeminal nerve. Nose nerve cells called "sneeze neurons" release a messenger called NMB when irritants such as capsaicin or histamine hit them, and in mice, knocking out the NMBR gene or giving NMBR blockers significantly inhibited the sneeze reflex, which helped show how the reflex is wired.

A sneeze has three stages: a big breath in as the diaphragm and rib muscles contract, a squeeze as the soft palate seals the back of the nose, then an explosive breath out as the glottis opens. The three-stage sneeze is run by a group of cells in the ventral medulla, which activates the breathing muscles and soft palate muscles. In a recent research review, the airflow in a sneeze was reported to reach nearly 100 kilometers per hour (about 60 miles per hour), and according to another research review, droplets from a sneeze can travel through the air for 7 to 8 meters and stay suspended for up to 10 minutes. A sneeze can send up to 40,000 tiny droplets out of the nose and mouth.

Some people sneeze when they step from a dim place into bright light, which is called the photic sneeze reflex. As of November 2026, estimates of how many people sneeze in bright light vary: about 25% in a 2025 research paper, one in three at Cleveland Clinic, and 10 to 30 percent in a PBS report. Scientists are not sure how light makes people sneeze. The most popular theory is that signals cross between the optic nerve and the trigeminal nerve, which senses facial feelings like an itchy nose. Photic sneezing has three main theories: the optic-trigeminal summation theory (the optic and trigeminal nerves cross wires in the midbrain), parasympathetic hypersensitivity, and parasympathetic generalization, and a 2025 paper says no solid evidence picks between them. A 2010 Swiss study of 10 photic sneezers found more stimulation of the visual cortex when they were exposed to light than in people without the reflex. Most photic sneeze research is small, and a 2016 Spanish study found thicker nerves in the cornea of people who sneeze at light, but all 13 people studied were from one family.

Your diaphragm is a muscle under your lungs that helps you breathe, and in a hiccup it jerks, or spasms, and you cannot stop it. Hiccups are a reflex: the diaphragm contracts suddenly, which causes a sudden intake of breath that is cut off when the glottis (the gap between the vocal cords) closes. In a hiccup, the diaphragm jerks so air rushes in fast, and then the vocal cords snap shut, which makes the "hic" sound. The vagus and phrenic nerves supply the diaphragm muscle, and irritation of these nerves is one cause of long-lasting hiccups. Eating too much or too fast, fizzy drinks and getting very excited can start hiccups, and most often they come from a stretched, full stomach.

Charles Osborne of Iowa hiccuped nonstop for about 68 years, from 1922 to 1990, the longest attack of hiccups confirmed by Guinness World Records as of November 2026. His hiccups began in 1922 after an accident while he was handling a hog on a farm. He lived a fairly normal life despite the hiccups: he married twice, had eight children and sold farm machinery. Osborne averaged 20 to 40 hiccups a minute and hiccuped an estimated 430 million times in all, though the total is an estimate, not a count. For reasons unknown, his hiccups suddenly stopped in 1990. If hiccups last longer than 48 hours (two days), a grown-up should take the person to a doctor.

Unborn babies hiccup too. A study that recorded 45 low-risk fetuses found that hiccups were the main diaphragm movement before 26 weeks of pregnancy. Fetal hiccups decrease as pregnancy goes on: in the 45-fetus study there was a pronounced drop between 24 and 26 weeks, from fewer episodes rather than shorter ones. Another theory says hiccups might stop babies from breathing in fluid in the womb, or train the breathing muscles for after birth. One theory says our hiccup reflex may come from our amphibian ancestors: tadpoles have a hiccup reflex that helps keep their lungs safe while they switch from breathing underwater. Yawning-like behavior has been seen in almost all vertebrates, which suggests that reflex, too, is very old.

People try many folk remedies for hiccups, such as holding their breath, sipping ice-cold water or swallowing a little sugar, and these are things people try, not proven cures. Britannica says they aim to interrupt the rhythm of the diaphragm spasms, and holding your breath for as long as possible is the most common one. One idea about why drinking through a paper towel is a folk cure is that sucking hard pulls the diaphragm down and may break the cycle of spasms, but this is one doctor's theory, not proven. The NHS says there is no evidence that home hiccup tricks work for everyone, though many people find them helpful, and a science article for children reports a big study that found none of them actually work.

A yawn lasts about four to seven seconds, and adults yawn about eight to nine times a day on average. Yawning is started in the brain by the hypothalamus and brainstem, with chemical messengers called neurotransmitters. In rodents, stimulating a region of the hypothalamus that contains oxytocin neurons causes yawning behavior, and one brain-scan study of people prone to contagious yawning found activity in the ventromedial prefrontal cortex, a region linked to decision-making. During a yawn the throat widens to three or four times its normal size, and the ears may pop as the eustachian tubes open. Muscles in the ear called the tensor tympani are activated, which may reset the range of movement and sensitivity of the eardrum and so help us monitor the world after we may have tuned out.

Fetal yawns were recorded with 4D ultrasound between 11 and 20 weeks of pregnancy, so yawning appears long before birth. Newborns and infants yawn often, which may be linked to their frequent switches between sleeping and waking. Contagious yawning does not fully show up in children until about age four or five. Other animals yawn too, including cats, dogs, birds and fish, and chimpanzees, our closest living relatives, yawn on their own and also catch yawns from each other.

The ancient Greek physician Hippocrates suggested that yawning removed bad air from the lungs and brought in good air; modern research has largely debunked this idea. Scientists used to think yawns bring in more oxygen, but studies did not support that idea, and a fetus gets its oxygen from the blood through the umbilical cord, yet it still yawns, which is one reason researchers doubt the oxygen idea. Three main theories try to explain yawning: it wakes up the brain, it cools the brain, or it sends a message to others. The arousal theory says yawning helps wake the brain up, because yawns are most common when people are drowsy or bored.

One idea, the brain-cooling theory, says a yawn pulls in cool air that cools the blood going to the brain. The idea has critics: a Swinburne University analysis says the research behind it shows yawning rises when brain and body temperature rise, but not that yawning cools anything. In a 2007 study led by psychology professor Andrew Gallup, people who were warmed yawned more at pictures of yawning, and people in a cooler place or with cold packs on their foreheads yawned less. In 2014, researchers from the University of Vienna measured contagious yawning outdoors in Vienna in summer and winter and compared it with an earlier Arizona study: people in Vienna yawned more in summer, and people in Arizona yawned more in winter. The Vienna team found that contagious yawning was limited to an optimal range of temperatures around 20 degrees C (68 F), and it faded when it was about 37 C (99 F) in Arizona summer or near freezing in Vienna winter.

The communication theory says a yawn may tell the people around you that you are bored or stressed, or that the place is not right, which could be why yawns spread. One evolutionary idea is the sentry-duty theory: social animals that share the job of keeping watch may use yawning or stretching to signal that someone is getting less alert and a new watcher is needed. The authors of the Vienna study suggest that contagious yawning spreading through a group could help the whole group stay alert. We are much more likely to catch a yawn from a close loved one than from a stranger.

Nobody knows for sure why we hiccup, and hiccups have no obvious purpose. One idea is that they did something useful in our distant relatives and never left us. Nobody knows for certain why we yawn, either: a Swinburne University article says we do not have evidence that points to the exact purpose of yawning, even though many triggers and the mechanism are well known. Researchers think contagious yawning is related to empathy, our ability to understand and share the feelings of another, but the idea is still being tested.

Words to know

• reflex: automatic body action
• medulla: lower brainstem
• photic: about light
• glottis: throat gap
• hypothalamus: brain region
• empathy: sharing feelings