You’re sitting in a long meeting, trying to concentrate, when someone across the room opens their mouth in a long yawn. Within seconds, you feel that irresistible urge rising — and, before you even realize it, you’re yawning too. It’s automatic, involuntary, and often embarrassing. But why does this happen?
Yawning is one of the most universal behaviors in the animal kingdom. Fish yawn. Birds yawn. Dogs, cats, chimpanzees, and even human fetuses in the womb — they all yawn. And yet, for centuries, science struggled to precisely explain what this simple and common reflex is for. Today, researchers have much more robust answers, and they are surprisingly fascinating.
In this article, we’ll dive into the physiology of yawning, explore the most accepted theories about its function, understand why it “spreads” when we see another person yawning, and discover what science still hasn’t fully explained about this seemingly mundane act.
What happens in your body when you yawn
Yawning — technically called oscitation — is a coordinated motor sequence involving several muscle groups at once. When we yawn, we open our jaw to the maximum, contract muscles in the neck and trunk, sometimes stretch our arms (which, along with the yawn, is called pandiculation), and breathe deeply. All of this in about 5 to 7 seconds.
During this process, the eyes close partially or completely, the eardrum membrane stretches, and the pharynx dilates. The heart may accelerate slightly. It’s a physiological event far more complex than it appears.
The reflex is controlled by deep areas of the brain, especially the hypothalamus and the brainstem — regions linked to automatic functions and the regulation of wakefulness. Neurotransmitters like dopamine, serotonin, nitric oxide, and hormones like ACTH (involved in the stress response) are associated with triggering yawning.
Why do we yawn? The main theories
For a long time, the most popular explanation was simple: we yawn because we need more oxygen. According to this theory, when the air is “stale” or when we’re drowsy and breathe more shallowly, yawning would be a way to inhale more O₂ at once.
The problem is that this hypothesis was tested and largely disproven. Studies conducted in the 1980s and 1990s showed that increasing or decreasing the levels of oxygen and carbon dioxide in the air that volunteers breathed did not alter how frequently they yawned. If it were just a matter of oxygenation, manipulating these gases should have changed everything — and it didn’t.
So, why do we yawn?
Brain cooling theory
One of the best-supported hypotheses today is that yawning serves to cool the brain. Research conducted by psychologist Andrew Gallup, especially from the 2000s onward, suggested that inhaling cool air and stretching the jaw muscles increases blood flow to the skull, functioning as a thermoregulation mechanism.
In Gallup and colleagues’ experiments, people yawned more when there was a greater temperature difference between the head and the environment. When temperatures were very high or very low, yawning decreased — suggesting it would be more effective within an intermediate range.
Arousal state regulation
Another widely accepted theory is that yawning functions as a state-transition mechanism. We yawn a lot when we’re waking up, when we’re about to fall asleep, when we’re bored, or when we need to concentrate on something new. This suggests it may help the brain shift “modes” — from drowsy to alert, or vice versa.
This theory also explains why athletes yawn before competitions and why musicians yawn backstage before going on stage: it would be a way for the nervous system to “calibrate” itself for a demanding task.
Social and evolutionary communication
There are those who argue that, over the course of evolution, yawning acquired a role in social signaling. In groups of animals, synchronized yawning could coordinate collective sleep and wake cycles — a way for the entire group to “agree” on when to rest or prepare for activity.
This leads us directly to the phenomenon of contagious yawning.
Why is yawning contagious?
This is, perhaps, the most intriguing aspect of yawning. Seeing someone yawn, hearing a yawn, reading about yawns — as you’re probably feeling right now — can trigger the reflex in another person. It’s estimated that contagious yawning affects between 40% and 60% of adults in trigger situations, although exact numbers vary between studies.
The role of empathy
Research points to a strong connection between contagious yawning and the capacity for empathy — the ability to recognize and share the emotional states of others.
Studies with children showed that contagious yawning begins to appear around 4 to 5 years of age, which is exactly when children develop what psychologists call “theory of mind” — the ability to understand that other people have thoughts and feelings different from their own.
Autistic children, who often experience difficulties with empathy and theory of mind, tend to be less susceptible to contagious yawning. This finding was observed in studies published by researchers like Molly Helt and collaborators and raised the hypothesis that susceptibility to contagious yawning may be an indirect marker of social and empathic abilities.
Mirror neurons
A popular neurological explanation involves the so-called mirror neurons — brain cells that activate both when we perform an action and when we observe another person performing the same action. These neurons were originally identified in monkeys and later found in functional evidence in humans.
The idea is that, when we see someone yawning, our brain “simulates” that action internally, and this may be enough to trigger the reflex. However, it’s important to note that the direct link between mirror neurons and contagious yawning is still debated in the scientific community — it’s a plausible hypothesis, but not definitively proven.
It also happens in animals
Dogs yawn in response to human yawning, and studies have shown that they are more susceptible to yawning from their owners than from strangers — which reinforces the idea that the phenomenon is linked to emotional and social bonds, not just mechanical imitation.
When excessive yawning may signal something more
For most people, we yawn several times a day without any special clinical significance. But frequent and excessive yawning, especially when there’s no apparent drowsiness, can, in some cases, be associated with medical conditions.
Situations that may increase yawning:
- Sleep deprivation
- Certain medications (such as anticonvulsants and antidepressants)
- Problems with body temperature regulation
- Neurological conditions such as epilepsy, multiple sclerosis, and, in some clinical reports, brain tumors
- Anxiety and chronic stress
It’s important to emphasize: this article is for general informational purposes. Any concern about excessive yawning or associated symptoms should be evaluated by a doctor or healthcare professional. Yawning by itself is rarely an isolated symptom of serious illnesses, but when accompanied by other signs, it deserves attention.
Fun facts about yawning
- Fetuses yawn: ultrasounds show babies yawning in the womb from around 11 weeks of gestation — long before they could feel sleepiness or boredom, suggesting yawning has a neurological developmental function.
- Fish and reptiles yawn: the reflex is so evolutionarily ancient that it’s present in cold-blooded vertebrates, which don’t have the same sleep regulation mechanisms as mammals.
- The “longest” yawn lasts around 10 seconds, although this varies individually.
- Just thinking about yawning is enough: simply reading the word “yawn” or a text describing the act can be sufficient to trigger the reflex in susceptible people.
- In Brazil, it’s popularly said that we yawn when someone is “missing” us. Of course, this is just folklore — but it’s an example of how yawning is embedded in culture.
What science still doesn’t know
Despite decades of research, yawning still holds mysteries. There is no definitive consensus on what its primary function is — brain cooling, state transition, social communication? Perhaps it’s all of these at once, with different weights in each context.
It’s also not completely clear why some people are much more susceptible to contagious yawning than others, nor why the simple image or description of the act is enough to trigger the reflex. These are active fields of research in behavioral neuroscience.
What science is making increasingly clear is that yawning — far from being a sign of laziness or disrespect — is a sophisticated reflex with deep roots in the evolution of vertebrates and unexpected connections to empathy and social cognition.
Conclusion
Yawning is much more than an inconvenient gesture in meetings or a way to make your sleepiness clear. It’s a physiological phenomenon with millions of years of evolutionary history, linked to brain regulation, states of attention, and, surprisingly, to our capacity to connect with others.
The next time you yawn — and you’ve probably yawned a few times while reading this text — remember: your brain is doing something much more interesting than simply “asking for air.” It’s regulating itself, synchronizing, perhaps even empathizing.
And if you want to continue on the theme of well-being and energy throughout the day, it’s worth checking out our content about foods that increase energy and vitality throughout the day — after all, what you eat also has a lot to do with how many times you yawn throughout the hours.
