I find yawning a little insulting to our ideas about self-control. You can be sitting there trying to look interested, competent and reasonably well rested, and your face decides to open as far as it can in front of everybody. Then, occasionally, somebody else's face joins in. An ordinary breath doesn't usually start recruiting people across the room, which makes this particular behavior considerably stranger than it first appears.
The question that interests me is why we have a yawn at all. We do it so often that it seems like something science should've explained by now, somewhere between figuring out digestion and sending equipment to Mars. Instead, there are experiments involving oxygen, rats with temperature probes, people watching videos of other people yawning, and MRI scans of what happens inside the head and neck. An awful lot of equipment has been pointed at an action we mostly try to hide behind a hand.
A yawn has a recognizable sequence
A human yawn usually involves a widening jaw, a long inward breath and a return toward ordinary breathing. The eyes may close, and the rest of the body sometimes joins in with a stretch. It takes a sequence of movements to produce the familiar event. Opening your mouth for the dentist and taking a deep breath can involve some of the same parts without being a yawn.
There's also a useful distinction between spontaneous yawning and contagious yawning. One can turn up without another yawner setting it off; the other is prompted by encountering someone else's yawn, as in the video experiments discussed below. Those questions overlap, but explaining why a movement spreads doesn't automatically explain why the movement exists. I think that's partly why the subject can get confusing so quickly. We ask one small question and accidentally bring several others along.
The extra-oxygen explanation didn't hold up
The familiar explanation is that yawning delivers extra oxygen when the brain needs it. Robert Provine and colleagues tested that idea in experiments published in 1987, comparing ordinary air with oxygen-rich or carbon-dioxide-rich gas mixtures in college-age participants. The altered gases didn't significantly change yawning as predicted. Exercise that doubled breathing rate didn't change yawning either, which argues against the idea that its main job is correcting those respiratory gases.
That's the sort of explanation I can see myself accepting without questioning it. A big breath looks as though it ought to be solving a need for air, and the story is easy to repeat. The experiment separates two things that appear to belong together: how much someone is breathing and whether they're yawning. A yawn includes a breath, but that doesn't tell us what sets the entire action in motion.
Being sleepy is still part of the story
Yawning and sleepiness certainly haven't parted ways. In a 2007 study, people who complained of excessive sleepiness were monitored while trying to stay awake in a darkened room. Yawns occurred during increased drowsiness, but the researchers didn't find a measurable rise in brain arousal afterward. A behavior appearing when we're struggling to stay awake doesn't prove it successfully wakes us up. Unfortunately, a dramatic opening of the mouth isn't a particularly reliable substitute for sleep.
Could yawning help cool the brain?
One proposed function is temperature regulation. The idea is that the movements and circulation changes surrounding a yawn could help manage heat around the brain. It's an interesting possibility, especially because it gives researchers something physical to measure. It also needs to stay a hypothesis with supporting experiments, rather than becoming a claim that every yawn means your brain was overheating.
In a 2010 rat study, researchers used probes to record brain temperature around yawns and stretches. Temperatures rose before those behaviors and fell afterward. Four rats contributed yawning data, so this was a small, preliminary study of an association. The pattern supports a possible thermal role, but it can't establish the purpose of every human yawn. I find the result fascinating without needing to turn my jaw into a thermostat.
There have been human experiments too. In a 2007 study, breathing through the nose and cooling the forehead reduced contagious yawning while participants watched yawning videos. The researchers interpreted those results as support for cooling. Measuring how often someone yawns under those conditions is still different from directly measuring what a particular yawn does to their brain temperature. That gap is useful to remember when a promising explanation starts sounding completely settled.
Researchers have now watched fluid move during a yawn
A 2026 MRI study added a detail I hadn't expected to find in an article about yawning. Scientists compared normal breathing, deep mouth breaths, yawns and stifled yawns in healthy adults. Both deep breaths and yawns increased movement of cerebrospinal fluid and blood flowing through veins compared with normal breathing, but the patterns differed. During yawns, cerebrospinal fluid and venous blood more often moved together toward the body during inhalation.
The study also found a distinct increase in blood entering through the internal carotid artery during part of the yawn. Those observations give researchers new ways to investigate circulation and possible heat exchange. They don't show that yawning cleans the brain, prevents a disease or makes someone think more clearly. What I like about the finding is how much movement is hidden inside an apparently simple action. From outside, we see a mouth open; inside, several things are changing together.
The urge can be harder to stop than the expression
The motor system is involved in contagious yawning too. In a 2017 experiment with 36 adults, researchers measured excitability and inhibition in the primary motor cortex using transcranial magnetic stimulation. Those measures predicted differences in how susceptible people were to contagious yawning. The motor cortex helps produce movement, and its readiness to respond appears to be an important piece of this particular behavior.
Being told to resist yawning increased the urge and changed whether participants produced full or stifled yawns, without changing their underlying susceptibility in that experiment. I find that especially funny because it separates looking composed from actually feeling composed. Your face may manage a smaller version of the event while the urge carries on. It also explains why telling a room full of people to stop yawning would be an entertainingly poor approach to making a meeting feel lively.
Catching a yawn doesn't tell us how much someone cares
The empathy explanation is appealing because contagious yawning looks social. One person does something, another responds, and it feels reasonable to connect that exchange with an emotional bond. There is research behind the idea. In a 2011 observational study, yawning spread more readily between relatives and friends than between acquaintances and strangers. That's an interesting relationship between social closeness and a visible response.
It doesn't give us a simple empathy meter, though. In a 2014 study of 328 people, participants watched a three-minute yawning video and completed questionnaires and other measures. Once age was taken into account, empathy scores didn't explain who caught the yawns. Age itself explained only a small share of the variation, leaving most of the differences unresolved. Some people were consistently more susceptible than others across testing sessions, and some didn't feel an urge at all.
I can understand wanting a small, visible sign that somebody feels connected to you. People are complicated, and a jaw opening on cue would be a very convienient shortcut through all that uncertainty. These findings don't give us that shortcut. Someone can watch a yawn without catching it, and we still haven't learned whether they listen carefully, remember what matters to another person or show up when they're needed. Those seem like much more useful things to notice.
The autism claim needs particular care
Some early accounts turned differences in contagious yawning among autistic children into a story about empathy. A 2009 experiment shows why the setup matters. Researchers presented yawning and control videos to 31 autistic children and 31 non-autistic children, with instructions to look at the eyes. Under those conditions, both groups yawned equally frequently in response to the yawning clips.
That result doesn't describe every autistic person or turn eye contact into a prescription. It shows that a reported difference can change with the way a task directs attention. Reducing a person's emotional life to whether they copied a facial movement loses an enormous amount, and it gives the movement a job the evidence doesn't support. A yawn response can't carry all the meaning people sometimes try to put into it.
A pleasurable stretch isn't proof of a nervous system reset
A yawn can feel satisfying, especially when a stretch comes with it. That subjective feeling doesn't establish a switch into one particular nervous system state. In a study published in 2012, researchers recorded several physiological measures around human yawns and found increases in heart rate and other changes during or immediately afterward. The details varied between their two studies. The event didn't reduce neatly to a heart slowing down and the whole body entering calm.
I'd be happy to enjoy a good stretch without requiring it to demonstrate trauma release, emotional healing or a reset of the vagus nerve. The experiments discussed here measured movements, responses to videos or physiological changes. They didn't establish voluntary yawning as a treatment for anxiety or grief. Feeling better after a moment is a real experience someone can describe; deciding which mechanism caused it is a separate question.
Dogs can catch yawns, but the love test still doesn't work
Dogs make the subject particularly tempting to romanticize. A person yawns, a dog yawns, and it's easy to see an affectionate little exchange taking place. Researchers have tested whether dogs respond differently to different people, including whether familiarity matters. It's a lovely question, but the results haven't supported the simple claim that a dog yawning after you demonstrates how deeply it loves you.
A 2020 analysis revisited six dog studies and found support for contagious yawning itself, but no evidence of the predicted familiarity or gender biases. In a further experiment, dogs also didn't yawn more after a person who had behaved helpfully than after one who hadn't. That challenges the empathy explanation while leaving the cross-species response interesting. We can be fond of an animal without making every shared movement a test it has to pass.
The movement appears before birth
One of the oddest details is that yawn-like movements can be studied in the womb. In a 2012 study, researchers followed 15 fetuses with ultrasound at about 24, 28, 32 and 36 weeks of pregnancy. They distinguished yawns from other mouth openings by looking at how long the mouth took to open and close. A still image at the widest point wasn't enough to separate them, which is a rather good reminder of how much information a photograph leaves out.
The researchers observed developmental changes in how often the movements appeared. That doesn't tell us a fetus is bored, sleepy in the adult sense or reacting to another person's yawn. It places the movement much earlier in life than a social explanation alone might suggest. Before any awkward meeting or attempt to stay awake for a film, parts of this familiar sequence are already appearing.
One ordinary yawn and a change worth noticing
For most of us, the familiar context is still tiredness or sleepiness. MedlinePlus notes that unusual, unexplained excessive yawning, particularly with marked daytime sleepiness, is something to discuss with a healthcare professional. Medicines can sometimes contribute too, so a persistent change deserves a look at the context rather than a self-diagnosis from a list of possible causes. It isn't a reason to treat an ordinary yawn as a medical event.
I also think we should allow ourselves to be tired without turning the feeling into a secret message. If someone yawns after a long or emotional day, we don't need to decide that their body has proved a particular healing process is complete. They might simply need some rest. There's kindness in accepting that fairly ordinary possibility, even if it doesn't make such an elaborate explanation.
I keep thinking about the unanswered part
We can measure the movement, change the conditions around it and watch how another person responds. We can record blood flow during it and distinguish a full yawn from a stifled one. Yet explaining why this particular sequence exists, and how its possible functions fit together, remains a live scientific question. I love that something this familiar can still make people build experiments around it.
There's a nice awkwardness to the whole subject too. A yawn can make a person look completely uninterested while the question behind it is actually fascinating, which seems rather unfair to anyone giving a presentation about yawning. If one slipped out while you were reading, you don't have to assign it a profound meaning. And if none did, your jaw has declined to participate, leaving all those questions for the rest of us.
Sources and further reading
Provine, Tate and Geldmacher (1987), oxygen, carbon dioxide and exercise
Shoup-Knox et al. (2010), brain temperature around yawns in rats
Gallup and Gallup (2007), nasal breathing and forehead cooling experiments
Martinac et al. (2026), MRI observations of yawning and fluid movement
Norscia and Palagi (2011), social closeness and yawn contagion
Bartholomew and Cirulli (2014), individual differences and empathy measures
Senju et al. (2009), attention and contagious yawning in autistic children
Corey et al. (2012), physiological changes around human yawns
Neilands et al. (2020), dog yawn contagion, reanalysis and experiment
Reissland, Francis and Mason (2012), fetal yawns and mouth openings
