All vertebrates yawn, or engage in a behavior that closely resembles yawning. Social baboons yawn, as do more solitary orangutans. Parakeets, penguins, and crocodiles also yawn—and the first jawed fish likely did too. Until recently, the reason for yawning was unclear, and it remains a topic of debate among researchers. However, this widespread behavior offers a clue to its true purpose—and it’s probably not what you think.
“When I ask audiences why they believe we yawn, most people say it’s related to breathing or respiration, and that it might boost oxygen in the blood,” explains Andrew Gallup, a behavioral biology professor at Johns Hopkins University. “That makes sense because yawning involves a deep breath. But what many don’t realize is that this idea has been tested and proven wrong.”
To check if yawning increases oxygen or removes carbon dioxide, studies in the 1980s adjusted the levels of these gases in the air volunteers breathed. They found that while these changes affected other breathing processes, they didn’t change how often people yawned. Additionally, there’s no clear difference in yawning between people with breathing-related illnesses and others, which wouldn’t be the case if yawning were tied to respiration.
This is where Gallup entered the field. “While working on my honors thesis, my advisor suggested studying yawning since no one knew why we do it,” he recalls. “That intrigued me—we knew it had to serve some physiological function. So I looked at the physical action: opening the jaw wide, taking a deep breath, then closing the jaw and exhaling quickly. It struck me that this might have important effects on blood flow in the skull.”
In fact, research supports this: medical reviews indicate that yawning boosts arterial blood flow to the head and improves venous return, the rate at which blood flows back to the heart.
“We can compare the jaw opening to a localized stretch, like stretching muscles elsewhere in the body,” Gallup says. “Just as stretching aids circulation in limbs, yawning seems to do the same for the skull.”
From there, Gallup and his team developed the theory that yawning helps regulate temperature in and around the skull. Brain temperature depends on three factors: the rate of arterial blood flow to the brain, the temperature of that blood, and the heat generated by brain activity. Yawning may influence the first two. When you yawn, the deep breath moves across the moist surfaces of your mouth, tongue, and nasal passages, similar to air flowing over a car radiator, carrying heat away through evaporation and convection.
Studies support this: ambient temperature affects how often we yawn. Yawning increases when it’s slightly too warm (as the radiator effect cools the brain) but decreases when it’s very hot (since other cooling methods like sweating take over) or when it’s colder.Contagious, isn’t it? A Turkish fox. Photograph: Anadolu/Getty Images
This may also explain why some medical conditions are linked to frequent yawning: either the conditions or the medications used to treat them can raise brain or body temperature. The idea that yawning relates to brain activity is supported by animal studies—mammals and birds with more brain neurons tend to yawn longer, regardless of their brain size.
That doesn’t mean other theories are completely ruled out. The most evidence-backed one is the “arousal change” theory: yawning helps the brain shift between states, like from sleep to wakefulness or boredom to alertness. Dr. Olivier Walusinski, a medical historian who has written extensively on the topic, suggests, “Yawning might help the brain switch from its default mode—used for daydreaming and recalling memories—to the attentional network that prepares the body for action. One way it could do this is by aiding the flow of cerebrospinal fluid, which surrounds and protects the brain and spinal cord.”
It’s possible this function evolved first, with temperature regulation emerging as a helpful side effect. Future studies on a wider range of animals may provide more evidence. The two explanations could also be connected: changes in mental state likely involve shifts in brain activity and temperature, increasing the need for blood flow and cooling. This would explain why yawning occurs when you’re bored—your brain might be ramping up activity to find a more engaging situation, raising its circulatory demands.
But what about contagious yawning? We’ve all experienced one person yawning, triggering others to do the same, even on screen. Some researchers think this contagious behavior strengthens group bonds, as it’s a genuine signal of tiredness, boredom, or alertness. However, since many solitary animals yawn regularly, it’s probably not yawning’s main purpose.
Gallup notes, “Contagious yawning might not have a specific function and could just be a byproduct of complex social cognition in highly social species.” In simpler terms, animals, including humans, have mirror neurons that activate both when performing an action and when observing others do it. Seeing someone yawn might trigger your mirror neurons, making you yawn too. Contagious yawning could also help synchronize group behavior, aligning everyone’s state from relaxed to active, as suggested by the arousal change theory.
A 2021 study on lions found that yawning can spread other behaviors—if one lion yawns and then starts walking, others may follow. Contagious yawning might also boost group alertness; if one baboon yawns, the whole troop could become more vigilant. Conversely, it might help calm the group before sleep.
So, in short: yawning is likely beneficial and helps your brain work better. And if you’ve been yawning to get a five-year-old to sleep, keep it up—it might actually be working.
Frequently Asked Questions
Of course Here is a list of helpful and concise FAQs about yawning designed to address common assumptions and provide clear accurate answers
General Beginner Questions
Q Why do we yawn I thought it was just because were tired or bored
A While tiredness and boredom can trigger yawning the leading theory is that it helps cool down your brain A cool brain operates more efficiently so a yawn is like a radiator for your head
Q Is yawning really contagious
A Yes it is highly contagious Seeing hearing or even thinking about someone else yawning can trigger your own This is linked to empathy and social bonding
Q Whats the purpose of a yawn
A The main purposes are thought to be regulating brain temperature and increasing alertness The big inhale cools the brain while the stretch of jaw muscles increases blood flow helping you become more focused
Q Do we yawn because our body needs more oxygen
A This is a very common belief but scientific studies have largely debunked it People dont yawn more in lowoxygen environments and breathing more oxygen doesnt reduce yawning
Deeper Advanced Questions
Q How does yawning cool the brain
A When you take a deep cool breath during a yawn it changes the temperature of the blood flowing to your brain The stretching of your jaw also increases blood flow in the area helping to dissipate heat
Q Why is yawning contagious Whats happening in the brain
A Contagious yawning is linked to the mirror neuron system in your brain which is involved in empathy and understanding others actions Its a subconscious form of social connection
Q Are there people who dont find yawning contagious
A Yes Young children and individuals on the autism spectrum or with schizophrenia are less likely to experience contagious yawning which supports the theory linking it to empathy and social processing
Q Can yawning be a sign of a medical problem
A In rare cases excessive yawning can be a symptom of an underlying condition such as a sleep disorder a brain condition or issues with body temperature regulation If its extreme and persistent its worth mentioning to a doctor
Practical
