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Why Do We Yawn and Why Is It So Contagious? · So That's Why

• 0:04
  Jen Oliver: Welcome to the So that's Why Podcast where we unpack the
• 0:07
  science behind everyday questions.
• 0:09
  I'm Jen.
• 0:10
  Chris Smith: I'm Chris.
• 0:11
  Matt Edmundson: And I'm Matt.
• 0:13
  Jen Oliver: Right, so picture the scene.
• 0:15
  You're in a meeting, it's not a terrible meeting, and you're not even that tired.
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  And then someone across the table yawns and within about five seconds,
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  you feel it creeping up on you.
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  Your jaw stretches, your eyes are watering.
• 0:31
  Why do we yawn and why on earth is it so contagious?
• 0:34
  Matt Edmundson: Yeah.
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  And hands up, how many people listening to this are yawning now?
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  Right.
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  Why does, uh, trying hard not to yawn somehow make the
• 0:44
  whole thing 10 times worse.
• 0:46
  Yeah, right.
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  I wouldn't spend an entire presentation basically vibrating
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  with some kind of suppressed yawns.
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  Jaws clenched my eye streaming.
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  Uh, whilst all trying to look completely engaged.
• 0:57
  Chris Smith: Yeah, we've all been there and the science
• 1:00
  here is genuinely fascinating.
• 1:02
  I know I always say that, but this really is genuinely fascinating this time.
• 1:05
  Jen Oliver: It is
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  Chris Smith: absolutely because what most people think is happening when
• 1:10
  they yawn is almost entirely wrong.
• 1:13
  Jen Oliver: So by the end of this episode, you'll understand why
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  yawning has very little to do with boredom and everything to do with
• 1:20
  what's happening inside your brain.
• 1:22
  Though that doesn't make it any less awkward when it happens, mid
• 1:26
  cent, mid-sentence in a meeting
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  Matt Edmundson: and the actual reason turns out to be, uh, something most
• 1:32
  people would never guess, which is exactly the kind of thing, uh, we, we
• 1:38
  just want to tell somebody out, tell somebody else about right immediately.
• 1:42
  Jen Oliver: Okay, so let's start with what actually happens during
• 1:45
  a yarn, because it's more complex than just opening your mouth wide.
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  So everyone is familiar with the process, aren't we?
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  You know, your jaw drops, your mouth opens wide.
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  You take in a long, slow breath.
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  Your ear drum stretch, your eyes might close.
• 2:00
  You might tear up who's yawning yet.
• 2:03
  Yeah.
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  And often there's a whole body stretch reflex accompanying it.
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  You know, it's actually got a technical term.
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  That whole full sequence is called pandiculation.
• 2:14
  Matt Edmundson: pandiculation.
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  Such a good word, isn't it?
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  I didn't even know my eardrums could stretch.
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  And now I'm learning about pandiculation.
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  Uh, I'm gonna try and work that into a conversation, uh, at least
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  once this week and see if anyone is.
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  Chris Smith: Yep.
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  Good luck with that.
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  Um, what's particularly interesting.
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  Is that it's, um, semi involuntary.
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  So it is triggered by your nervous system and once it kind of begins, you
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  genuinely can't stop it midway through.
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  And researchers have identified that at least seven distinct, um,
• 2:45
  physiological steps are in that sequence.
• 2:47
  Matt Edmundson: Seven, seven coordinated steps to open your mouth.
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  Uh, the question is my body massively over complicating basic tasks here?
• 2:56
  Jen Oliver: Yeah.
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  Right.
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  But you know what?
• 2:59
  It has it, there's a formal study of yawning and it even has its own name.
• 3:04
  Matt Edmundson: Drum roll.
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  Jen Oliver: Cosmology.
• 3:07
  Matt Edmundson: Cosmology,
• 3:08
  Jen Oliver: yeah.
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  Because you, I'm a Cosmologist Doctor of Yawning doesn't sound quite as good
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  as Doctor of Cosmology does it, but it's a legitimate scientific field,
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  which gives you a sense that researchers in this field take this rather more
• 3:23
  seriously than the rest of us do.
• 3:25
  Chris Smith: They certainly do, and the most persistent misconception
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  with yawning is the oxygen theory.
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  So the idea that we yawn because our blood levels drop or the carbon dioxide
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  level in the blood builds up and that that big hail inhale is kind of corrected it.
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  That explanation has been comprehensively disapproved.
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  Jen Oliver: So there was a key study published in the Journal for re
• 3:48
  physiology and behavior and researchers.
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  They manipulated the oxygen and carbon dioxide content of the air
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  that participants were breathing in, and they measured whether it
• 4:00
  changed the yawning frequency.
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  And guess what?
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  It didn't at all.
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  Matt Edmundson: It did not.
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  No.
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  Uh, so the oxygen explanation then is completely wrong, and
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  yet it's probably the most common answer I would've given anyway.
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  And it's a great example, I suppose, of effect that survives purely on confidence.
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  Mm-hmm.
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  Chris Smith: And so if it's not oxygen, you're probably wondering.
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  What is actually going on?
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  And now the, um, the leading theory is that it centers on
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  brain temperature regulation.
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  So your bo your brain operates best within a very narrow temperature window,
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  and yawning appears to be one of its mechanisms for staying within that range.
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  Jen Oliver: Yeah, and there's a researcher at Princeton University
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  and he published work showing that when people held warm packs to their
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  foreheads, the number of times that they yawned it significantly increased.
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  But when they held cool packs to their heads.
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  That number drops dramatically, even below baseline.
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  Chris Smith: Yeah.
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  And the mechanism of this is pretty elegant.
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  So that deep inhale during a yarn draws cooler air across the palate,
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  which sits directly beneath the brain while the stretching of the jaw
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  muscles increases local blood flow.
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  And both of these effects work together to cool the tissue around the.
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  Matt Edmundson: So it's basically a built-in cooling fan, like
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  a car radiator for the brain.
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  Um, so I'm gonna be thinking about that every time I yawn them.
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  Jen Oliver: It also explains something that you may or may not know depending
• 5:26
  upon your background, but athletes often yawn in the changing room just
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  before they compete, and that that's their brains are ramping up, getting
• 5:34
  focused and anticipating the physical demands that are about to happen.
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  And their body is already one step ahead by triggering that cooling.
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  Chris Smith: Yeah.
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  So from the athletes to the rest of us, I mean, I'm not saying we're
• 5:47
  not all athletes, of course, um, there's also consistent evidence of
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  increased yawning during transitions between sleep and wakefulness.
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  So both times are when the brain's temperature and alertness.
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  Um, levels are changing quickly, so yawning seems to be your, the
• 6:05
  wave of your brain recalibrating.
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  Matt Edmundson: Okay, so the big morning yawn and stretch isn't just a cliche.
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  Um, it's your brain requesting a recalibration before it actually
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  has, before it actually has to think properly, I suppose.
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  That's quite relatable, isn't it?
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  Jen Oliver: Mm-hmm.
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  And did you know it actually starts remarkably early.
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  So ultrasound imaging shows yawns in fetuses of around 11 weeks gestation.
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  At that point, their lungs aren't even functional, so
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  it can't be about breathing.
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  Instead, it's thought to help jaw muscle development and
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  regulate brain fluid dynamics.
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  From a really early stage.
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  Matt Edmundson: That's really cool.
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  That's really amazing, isn't it?
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  Baby is doing biology homework in the womb.
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  I just, that is amazing.
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  Yeah.
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  Chris Smith: And um, it's a good reminder that yawning is doing
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  something genuinely fundamental.
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  It's not just kind of filling time during a slow afternoon.
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  Jen Oliver: Okay, so let's get to the part everyone wants to know
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  about contagious yawning, and fair warning, even talking about yawning
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  in a studio is probably triggering some of you listening to us right now.
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  Matt Edmundson: Mm-hmm.
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  Chris Smith: I know.
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  I'm totally stifling the yawning.
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  Stop, stop, stop.
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  I
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  Matt Edmundson: like how you said fair warning.
• 7:14
  Well hard way through the podcast.
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  Chris Smith: Um, so contagious.
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  Yawning is really well documented and remarkably widespread.
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  So it's been, um, observed in humans, of course, but also chimpanzees,
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  wolves, dogs even parakeets.
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  So yawning clearly goes beyond a simple involuntary reflex in humans.
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  Matt Edmundson: I love that.
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  A parakeet, yawning, catching yawns from each other.
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  Uh, that's like, well, let's just say that's probably the most
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  unexpected fact I've heard today.
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  Jen Oliver: They are.
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  And what's really interesting is that in social animals contagious yawning, it
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  seems to have like a synchronizing effect.
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  So it helps align the alertness or the brain state of everyone in the group.
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  Chris Smith: Yeah.
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  And in humans, um, contagious yawning is thought to involve mirror neuron systems.
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  So it's the same neural circuitry that underlies empathy.
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  And social imitation.
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  So when you hear, hear, see, or even read about someone yawning, part of
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  your brain simulates the experience, which then triggers the reflex itself.
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  Jen Oliver: I can feel my jaw out.
• 8:18
  Matt Edmundson: Don't start yawning.
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  'cause uh, you can't actually watch among yarn without feeling it.
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  No.
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  Can you, and I'm, you're gonna set us all off and apparently, like you say,
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  you can't even read the word yawn.
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  Uh, without your jaw starting to get its own ideas.
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  Uh, and like you guys, now I'm just fighting a yawn.
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  Just, just take the camera off me is probably the best way.
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  Jen Oliver: But you know, the research actually supports that experience.
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  So one study in a psychology journal, it looked at whether people's
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  susceptibility to contagious warning was linked to their empathy scores.
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  So they found a positive connection.
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  The more empathetic people said they were.
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  The more likely they were to catch a yawn.
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  Chris Smith: They did.
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  And it was so interesting, but it's worth, uh, being a bit careful with
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  the link because on the flip side, a Duke University study with over
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  300 participants found that while age and time of the day had stronger
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  effects on contagious yawning than expected, the empathy correlation
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  was less consistent than earlier, smaller studies have suggested.
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  So it's a bit of a mixed bag of results so far.
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  Jen Oliver: So the empathy link may be real, but more modest
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  than the headlines made it sound.
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  Which is a pattern that comes up regularly, doesn't it?
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  When smaller psychology findings get replicated at a larger scale.
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  Matt Edmundson: Okay, so translation, then you can reliably tell, uh, sorry.
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  You can't, uh, reliably tell anything meaningful about someone based on
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  whether they yawned back at you.
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  Chris Smith: Well.
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  You say that there's some really interesting research
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  on exactly that front.
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  So a study published in 2015 looked at individuals with higher
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  psychopathic traits and found they are significantly less susceptible
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  to contagious yawning than those without their psychopathic traits.
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  Jen Oliver: And that finding was followed up by even more research, which found
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  that people scoring higher on psychopathy measures, they showed reduced contagious
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  warning even after controlling for variables like sleep quality or age.
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  Matt Edmundson: So basically, if you are completely unmoved while everyone
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  around you is your, and either.
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  You've slept brilliantly or you might wanna take yourself off and
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  have a quiet word with yourself.
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  Chris Smith: So to be clear, as a total disclaimer, not catching a yawn doesn't
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  diagnose anything, and it doesn't make you a psychopath, and there is significant
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  individual variation regardless.
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  But what this thing does do is add another data point to a growing
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  body of research, linking certain social reflex responses to empathy.
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  Jen Oliver: And there's also something interesting about why we suppress yawning
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  in social situations because there's actually no biological benefit to it.
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  You know, fighting a yawn gives you jaw tension without giving
• 10:58
  you any of the cooling effect,
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  Matt Edmundson: which makes a lot of sense if you've.
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  Been in the meetings where I've, you know, sat and you can't yawn.
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  Uh, you spend so much of your energy not doing it, don't you?
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  Mm. Um, and that you've actually got nothing left to focus on the meeting with,
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  Chris Smith: which is exactly it.
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  So, most of what's, um, socially uncomfortable about
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  yawning is purely the context.
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  So, in a meeting, it can read.
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  Being disengaged, but as Jen said, in a sports changing room
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  before a match, it apparently reads as like, focus, preparation.
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  So the biology is identical in both cases,
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  Matt Edmundson: which means the only thing that actually changed
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  is the room you walked into.
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  Uh, in those two things, your brain is doing exactly the same
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  thing in both places, completely indifferent to how it looks.
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  Jen Oliver: But I think it is also worth covering when yawning becomes
• 11:52
  a signal worth paying attention to.
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  You know, occasional yawning is completely normal.
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  I saw that yawn, Chris
• 12:00
  Chris Smith: Yawn,
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  Matt Edmundson: but.
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  Jen Oliver: We're
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  Matt Edmundson: obviously not psychopaths.
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  That's the main
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  Jen Oliver: thing.
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  No, that's good.
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  Occasional yawning, like I said, is completely normal, but excessive yawning,
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  particularly when it's unprompted by tiredness or boredom, that can
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  sometimes be associated with conditions like migraines, epilepsy, or in rare
• 12:20
  cases, cardiac or neurological events.
• 12:22
  Chris Smith: That's it.
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  And the mechanism.
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  There involves the thermo regulatory and autonomic nervous system disruption
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  that accompanies those conditions.
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  It's the brain triggering its temperature management responses more
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  frequently as a result of a kind of broader, uh, physiological stress.
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  Matt Edmundson: So excessive out of the, out of nowhere yawning
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  is genuinely worth mentioning to your doctor, is what we're saying.
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  Uh, which is one of those things, I don't know, maybe you wanna
• 12:48
  bring up at the next appointment.
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  Jen Oliver: Exactly.
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  It's not something to catastrophize over.
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  But it's a reminder that yawning is a genuine physiological signal rather
• 12:58
  than just an embarrassing habit.
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  Matt Edmundson: I guess it's a bit like how your body
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  uses pain as a signal, right?
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  Mm-hmm.
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  Um, you don't ignore it entirely, uh, but you also don't panic every time
• 13:08
  your knee aches after a long walk.
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  Chris Smith: Yeah, it's a good way to put it.
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  So context is everything, and most of the time yawning is just
• 13:14
  your brain quietly going about its business, which is the much more
• 13:17
  likely explanation when it happens and there's something more serious.
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  Matt Edmundson: So when you put all of that together, it's actually
• 13:23
  a pretty different picture of yarning than most people start with.
• 13:27
  Certainly I did.
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  It's your brain doing active housekeeping, regulating temperature.
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  It's managing state transitions and potentially synchronizing
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  with the people around you.
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  Uh, it's not a sign of laziness or rudeness, even if those
• 13:42
  things can sometimes trigger it.
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  Chris Smith: Yep.
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  And that reframe is pretty useful to be fair because I think most people spend a
• 13:48
  lot of energy feeling embarrassed about something that their brain is just kind of
• 13:52
  quietly getting on with in the background.
• 13:54
  Jen Oliver: Yeah.
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  And you know, like everything, the more you understand what's driving
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  it, the less it feels like something happening to you and more like
• 14:02
  something your body's doing for you.
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  You know, and the sleep connection surprise surprise is worth flagging too.
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  You know, sleep deprivation that increases your infrequency, which ties directly into
• 14:14
  what we've covered in previous episodes on sleep quality and cognitive performance.
• 14:18
  You know, well-Rested Brains works so much better.
• 14:21
  Matt Edmundson: Have we talked about a sleep before in this podcast?
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  I
• 14:24
  Jen Oliver: don't know.
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  We might have of,
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  Matt Edmundson: might have figured that.
• 14:25
  Um, but if you find yourself yawning more than usual and nothing else
• 14:30
  has changed, uh, it's worth asking whether your sleep has taken a bit of
• 14:34
  a hit, um, not as something to stress about, just as useful information
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  your body is handing over to you.
• 14:40
  Chris Smith: Yeah, and that's, um, probably the most practical takeaway of
• 14:43
  all of this, like yawning is a readout.
• 14:45
  It's telling you something about your brain state and how well rested you are.
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  And most of the time it's completely benign.
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  But it is worth noticing to keeping an eye on.
• 14:54
  Matt Edmundson: So next time you're in a meeting, right,
• 14:56
  and you feel you are building.
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  You're not being rude, which is a wonderful thing.
• 15:00
  You are performing precision brain cooling.
• 15:04
  That's a much better way to look at it.
• 15:05
  Mm-hmm.
• 15:06
  Um, and it should be maybe something we should be allowed to say out loud.
• 15:09
  Chris Smith: Absolutely.
• 15:10
  And it really is that fundamental.
• 15:11
  So yawning is one of the most observed behaviors across vertebrates existed.
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  Fish in reptiles, in birds, in mammals.
• 15:19
  We talked about parakeets.
• 15:20
  Um, that tells you it's solving a genuinely important problem, not just
• 15:24
  a quirk of, you know, human biology.
• 15:26
  Okay,
• 15:26
  Jen Oliver: so that's why we yawn and why it's contagious.
• 15:30
  Yawning mainly helps regulate brain temperature.
• 15:33
  Your nervous system brings in cooler air across the palette and boost blood flow
• 15:38
  to keep the brain working at its best.
• 15:41
  Contagious, yawning taps into the same brain networks that handle empathy
• 15:45
  and imitation, which is why just seeing, hearing, or even thinking
• 15:49
  about a yarn can set you off on one.
• 15:52
  Chris Smith: And it starts in the womb.
• 15:53
  It works across different species and it has nothing to do with
• 15:57
  oxygen levels, despite that being the explanation that most of us
• 16:01
  have carried for our entire lives.
• 16:02
  Jen Oliver: Mm-hmm.
• 16:03
  Matt Edmundson: Yeah.
• 16:03
  So your brain is just hot sometimes.
• 16:05
  Um, so it cools itself down, which is very reassuring.
• 16:10
  Jen Oliver: It is indeed.
• 16:12
  You can all yawn now safely.
• 16:14
  So that's it for this week.
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  Make sure you hit that subscribe button.
• 16:17
  We're gonna keep unpacking the science behind everyday questions.
• 16:22
  Tell us in the comments what you'd like us to explore.
• 16:25
  Thanks for geeking out with us.
• 16:26
  But for now, that's it from me.
• 16:28
  Matt Edmundson: That's it from me.
• 16:29
  Chris Smith: And that's it from me.
• 16:30
  Jen Oliver: Bye for now.