Monday, April 1, 2013

Why do we yawn?

Why do we yawn?

baby yawning
Yawning is such a common, everyday phenomenon that we scarcely pay any attention to it. Although most people put it down to tiredness or boredom, the truth is far more complex and mysterious.

Common beliefs about yawning

In 1986, Dr Robert R Provine (a world authority on yawning research) stated “at present, yawning may have the dubious distinction of being the least understood, common human behavior.”1 Over 30 years later, we’re still not that much wiser and this has led to a number of misconceptions and over simplifications. The three most common associations with yawning are:
Yawning is most commonly associated with being tired or sleepy. Scientists have demonstrated that yawning most frequently occurs during the hours before you fall asleep and just after you wake up.2 In a separate study EEG recordings confirmed that a sleepy brain will indeed prompt yawning behaviour.3
As well as sleepiness, yawning seems to be inextricably linked to situations where we feel bored or are lacking stimulus. The boredom hypothesis was demonstrated in an experiment which subjected students to 30 minutes of a television test bar pattern whilst another group watched 30 minutes of music videos.4 The first group yawned on average 70% more, confirming the belief that people yawn more during uninteresting as opposed to more interesting, stimulating events.
3:Oxygen deprivation
There’s a widely held belief that yawning is a mechanism to allow more oxygen into the body and/or expel carbon dioxide. According to this theory, when we get tired we breathe more slowly, reducing the amount of oxygen into the lungs. This causes a carbon dioxide build up in the blood, signalling the brain to take a deep breath, whereby a yawn is produced. Although there’s a certain logic to this assertion, it’s almost certainly a myth. The ‘oxygen/CO2′ theory was tested in 19875 and the results showed that CO2 deprivation did not result in increased yawning, nor did an enriched oxygen supply decrease instances of yawning.
A comprehensive 2010 review by Adrian G Guggisberg supported these findings, stating “…given current evidence, it seems unlikely that yawning has respiratory or circulatory functions.6

Other theories

Yawning cools the brain

One of the more popular theories of recent years has been that yawning is a way to cool down an overheated brain. Two studies support this theory, the first found that applying cold packs to the subjects’ heads practically eliminated contagious yawning.7 The second study8 found that yawning frequency differed from season to season and was more likely to occur when the outside temperature is either equal to or higher than internal body temperature.

Untested theories

Many other theories have been spawned over the years concerning yawning and its’ regulatory function on body physiology. Even Hippocrates, the father of medicine hypothesized about yawning, imagining it as a means of removing bad air from the lungs. Some more recent ideas include:
  • yawning stretches out the lungs and nearby tissues, preventing them from collapsing in a condition known as atelectasis (Cahill, 1978);
  • yawning distributes a chemical called surfactant, a fluid that coats the airways in the lungs and helps to keep them open. (Forrester, 1988);
  • yawning is linked to blood cortisol levels and a number of neurological disorders such as multiple sclerosis and stroke (Thompson Cortisol Hypothesis, 2011)
Although these may be true, none of these propositions have been experimentally tested.

Yawning as a social phenomenon

In recent years, much of the research has moved away from physiological explanations towards the idea that yawning may serve a communicative or sociological purpose. Some have postulated that yawning is a remainder of our distant evolutionary past – a subtle means to coordinate the actions of a social group, similar to the herding behaviour found in flocks of birds. Others hypothesize that yawning may be associated with “mental state attribution”9 ie the ability to see things from someone else’s point of view.
One experiment found that students who scored highly on tests of empathy, yawned more in response to videos of other people yawning. This ‘contagious’ quality of yawning is strongest when people are related or are close friends10 The effect is so powerful it has even been observed across different species. A 2007 study11 showed that 21 out of 29 dogs yawned when shown videos of yawning humans.
Dogs can catch yawns from humans. (CLICK FOR VIDEO)


Sadly there doesn’t seem to be a single ‘unified theory’ about the causes and functions of yawning. While it’s clear that some physiological factors such as sleepiness and boredom play key roles in triggering yawning, recent research into empathy and contagious yawning is starting to unravel the complex social interactions that can cause a chain reaction in humans and other species.
Many questions are yet to be answered. Is yawning just a vestigial remainder from our primitive evolutionary past? Could it be an indicator of vital bodily functions and potential illnesses? Or maybe it’s a subconscious form of communication we have yet to fathom? More research is needed but for now, yawning remains a mystery.
If you want to find out more about the world of yawning, check out the excellent archive at
photo by: twob


  1. Yawning: Effects of stimulus interest. R. R. Provine and H.B.Hammernik. Bulletin of the Psychonomic Society, 24, 437-438.
  2. Yawning: Relation to sleeping and stretching in humans. R. R. Provine, H. B. Hamernik, and B. C. Curchack. Ethology, 76, 152-160.
  3. The functional relationship between yawning and vigilance. Guggisberg AG, Mathis J, Herrmann US, Hess CW. Center of Sleep Medicine, Department of Neurology, Inselspital, University of Berne, CH-3010 Bern, Switzerland. Behav Brain Res. 2007 Apr 16
  4. Yawning as a stereotyped action pattern and releasing stimulus. R. R. Provine. Ethology, 72, 109-122.
  5. Yawning: no effect of 3-5% CO2, 100% O2, and exercise. Provine RR, Tate BC, Geldmacher LL. Department of Psychology, University of Maryland Baltimore County. Behav Neural Biol. 1987 Nov;48
  6. Why do we yawn?Adrian G Guggisberg, Johannes Mathis, Armin Schnider, Christian W Hess University of Geneva, Department of Clinical Neurosciences, Division of Neurorehabilitation. DOI:10.1016/j.neubiorev.2010.03.008
  7. Yawning as a brain cooling mechanism: Nasal breathing and forehead cooling diminish the incidence of contagious yawning. Andrew C. Gallup, Department of Psychology, State University of New York at Albany, Albany, NY 12222 Evolutionary Psychology 5
  8. Contagious yawning and seasonal climate variation. Andrew C. Gallup, Omar Tonsi Eldakar. Department of Biological Sciences, Binghamton University, Binghamton, NY, USA. Center for Insect Science, University of Arizona, Tucson, AZ, USA
  9. Contagious yawning: the role of self-awareness and mental state attribution. Platek SM, Critton SR, Myers TE, Gallup GG. Department of Psychology, State University of New York at Albany, Albany, NY, USA. Brain Res Cogn Brain Res. 2003 Jul
  10. Yawn Contagion and Empathy in Homo sapiens. Norscia I, Palagi E (2011). PLoS ONE 6(12).
  11. Dogs catch human yawns. Ramiro M Joly-Mascheroni, Atsushi Senju, Alex J Shepherd. School of Psychology, Birkbeck, University of London, Malet Street, London

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