Why Do We Yawn and Why Is It Contagious?

And there’s more: why does someone else’s yawn — or even just reading about it — make us yawn too? This “contagious” characteristic of yawning reveals something profound about how the human brain functions in society. Let’s explore all of this.

What Exactly Is a Yawn?

From a physiological standpoint, yawning — technically called pandiculation when accompanied by stretching — is an involuntary reflex that involves prolonged opening of the mouth, a deep inhalation of air, followed by a shorter exhalation. The process lasts, on average, from 4 to 7 seconds and is accompanied by contractions of the jaw, throat, and chest muscles.

The reflex is controlled by deep structures of the brain, especially the hypothalamus — a region that regulates basic functions such as sleep, body temperature, hunger, and emotions. Neurotransmitters like dopamine, serotonin, and nitric oxide have been identified as participants in the process, indicating that yawning is connected to much more complex systems than simply “needing air”.

Theories on Why We Yawn

For centuries, the most popular explanation was that we yawn because the brain is lacking oxygen. The logic seemed obvious: when we are bored or tired, we breathe more slowly, CO₂ increases in the blood, and yawning would be a way to “ventilate” the system.

The problem? This theory was tested and largely discarded. Studies conducted in the 1980s and 1990s — particularly the work of researcher Robert Provine from the University of Maryland (USA), who became a world reference in the study of yawning — demonstrated that increasing the concentration of oxygen or CO₂ in the air participants breathed did not alter the frequency of yawns. In other words, lack of oxygen does not explain the phenomenon.

So, what does explain it? The most accepted hypotheses currently by the scientific community are:

• Brain Temperature Regulation: One of the most robust theories, developed and defended especially by researcher Andrew Gallup from Princeton University (USA), suggests that yawning functions as a brain cooling mechanism. Opening the mouth and inhaling fresh air would increase blood flow and lower the temperature of the cerebral cortex, improving its functioning. Studies with rats and humans have shown that the frequency of yawns increases when the ambient temperature is closer to body temperature — and decreases when the environment is cooler.
  • Transition of Alert States: Yawning seems to occur more frequently at moments of state change — upon waking, falling asleep, before a stressful situation or effort. This suggests it may function as a neurological “reset”, preparing the brain for a new phase of activity.
    • Ear Lubrication: The contraction of muscles during yawning opens the Eustachian tubes (the channels that connect the throat to the middle ear), which can balance pressure in the ears — hence yawning is common during airplane takeoffs and landings.
      • Muscle Stretching: Pandiculation — yawning with stretching — may serve to activate muscles and joints that have been immobile for long periods, functioning as a kind of “passive warm-up” for the body.

        It is important to highlight that these are scientific hypotheses in development, and none of them is universally accepted as a definitive explanation. Yawning likely fulfills more than one function at the same time.

        Why Is Yawning Contagious?

        Here is the part that really intrigues researchers. Contagious yawning — the one that occurs when we see, hear, or even think about someone yawning — is a documented phenomenon in humans and some other animals, such as chimpanzees, baboons, domestic dogs, and even wolves.

        The main current theory links contagious yawning to empathy and social processing of the brain. Neuroimaging studies (which photograph the brain in activity) have identified that during contagious yawning, regions associated with empathy and social cognition are activated — especially the inferior frontal gyrus and parts of the mirror neuron system.

        Mirror neurons are brain cells that fire both when we perform an action and when we observe someone performing the same action. They are considered fundamental for imitation, social learning, and empathy. Contagious yawning would be, in this view, a primitive and automatic form of social synchronization — a sign of belonging to the group.

        Some data that reinforce this connection:

        • Children with autism, who often have difficulties in social processing and empathy, tend to yawn less in response to someone else’s yawn than neurotypical children — although they yawn normally for other reasons.
        • Contagious yawning seems to be stronger among emotionally close people: a study published in the journal PLOS ONE in 2011, conducted by Italian researchers, showed that the phenomenon is more frequent among family members and close friends than among strangers.
        • Contagious yawning develops in children around 4 to 5 years of age, coinciding with the period when the ability to recognize and share others’ emotions matures.
          

          When Yawning Can Signal Something More

          In the vast majority of cases, yawning is absolutely normal and healthy. However, excessive and frequent yawning — unrelated to sleep or boredom — can, in some cases, be a symptom of conditions that deserve medical attention.

          Among the situations that health professionals may investigate are:

          • Sleep disorders, such as obstructive sleep apnea
          • Problems with body temperature regulation
          • Neurological conditions, such as epilepsy or brainstem injuries
          • Side effects of certain medications, especially antidepressants that act on serotonin
          • Hypoglycemia (drop in blood sugar level)

            Attention: this article is for general informational purposes. Any concern related to the frequency or intensity of yawns should be evaluated by a healthcare professional, who can analyze the history and individual conditions of each person.

            Curiosities You Probably Didn’t Know

            • Octopuses yawn. Researchers have recorded the behavior in cephalopods (mollusks like octopuses and squids), which further broadens the idea that yawning is a very ancient evolutionary reflex.
            • Yawning while reading about yawns is as real as yawning when seeing someone yawn. Studies confirm that even the mental representation of yawning — text, audio, image — is enough to trigger the contagious reflex.
            • The average duration of a human yawn is 6 seconds, but it can vary greatly from person to person and situation to situation.
            • Yawning at work is not necessarily laziness. It may be a sign that the brain is trying to stay alert in a monotonous situation — a kind of attempt at self-regulation.
              

              Yawning Throughout History and Culture

              Historically, yawning has been interpreted in very different ways by different cultures. In Greco-Roman antiquity, it was believed that yawning was dangerous — the soul could escape through the open mouth, and covering the mouth was an act of protection, not politeness. Some cultures associated yawning with bad omens or the entry of spirits.

              In the contemporary world, yawning in public is still seen as impolite in many Western cultures — hence the gesture of covering the mouth, which remains a social norm even when the original explanation has been forgotten. In some East Asian cultures, yawning in public is viewed with less social stigma.

              This cultural variation shows how a purely biological reflex can be deeply shaped by social norms — and how humans are, at the same time, animals and cultural beings.

              Conclusion: A Simple Reflex, a Window to the Brain

              

              Yawning is one of those phenomena that seem trivial on the surface, but when examined closely, reveal the extraordinary complexity of the human organism. It involves temperature regulation, the neuroscience of empathy, evolutionary biology, and cultural norms — all in a gesture lasting a few seconds.

              Science has not yet exhausted the answers. And perhaps it is exactly this that makes yawning so fascinating: it reminds us that there is much to discover about behaviors we consider too obvious to question. The next time you yawn — or make someone next to you yawn — know that your brain is executing a program with millions of years of evolutionary history.

              If you are curious about other topics that science studies in surprising ways, it’s worth checking out Top Documentaries to Learn From: The Best Picks Right Now, where we gather productions that turn everyday life into learning.