We all do it. It’s a force of nature that can be embarrassing at times. If it’s excessive, it can be downright annoying and disrupting. Somehow it seems to be contagious.  I don’t think anybody can get through life without yawning thousands of times.

Just how many times does the average human yawn in a lifetime?

A better question: what exactly is a yawn?

You’d think I would have covered this question before, given the fact I’m a sleep expert and yawning is frequently associated with tiredness. But when I read a funny, brief article about yawning the other day that suggested yawning could signify erotic arousal, I decided to dig a little further into this mystifying world of a mouth wide open for a few seconds.

Technically, a yawn is a reflex of simultaneous inhalation of air and stretching of the eardrums, followed by exhalation of breath.  I know you are glad to have that explained.  But it’s the why that has most people curious, rather than the what.

Is a yawn always linked to exhaustion, fatigue or the need for sleep? Actually, no. Yawing can be connected to any number of conditions and even emotions, including stress, boredom, lack of stimulation (which can be code for boredom), and being overworked (another code for tiredness). I have no idea why yawning can be so “contagious”—watching some yawn (or, for that matter, just hearing someone yawn or even thinking of yawning) can trigger you to yawn as well. Are you yawning yet?

Strangely, we don’t actually know why we yawn. Just as sleep remains much a mystery, so does this universal human behavior. And, actually, most animals yawn. A single yawning shark can set off a yawn reaction in the entire school. A few theories exist, though, to explain human yawning:

  • Do increased amounts of carbon dioxide in the blood induce yawning to bring in oxygen? This theory has been around since Hippocrates, but studies have since shown it to be either incorrect or flawed. Why? Because yawning may, in fact, reduce oxygen intake compared to normal respiration (breathing), not increase it.
  • Is yawning the body’s way of controlling brain temperature? This theory suggests that yawning cools off the brain much like a fan cools the insides of a computer. Reptiles, for instance, might yawn to maintain their body temperature. Since most reptiles rely on ambient temperature to maintain body temperature, yawning might be a means for promoting rapid cooling down. This may also work for animals that don’t sweat. Pigs and dogs may yawn because they don’t sweat. Exposing the mouth and tonsils to the outside air may cool down the head, even if only by a few tenths of a degree.
  • Does yawning satisfy the need to stretch your muscles?
  • Is a yawn associated with nervousness?
  • Do yawns help you to stay alert?  Some studies have suggested that yawning—especially “contagious” yawning—may have developed as a way of keeping a group of animals alert. Anecdotal evidence suggests that yawning helps increase the state of alertness of a person. Paratroopers, for instance, have been noted to yawn in the moments before they exit the aircraft.
  • Is yawning a sign of dominance? Observation of dog and primate behavior has shown that alpha males and alpha females tend to yawn more frequently than do their beta counterparts. Yawning may actually be considered aggressive in certain species, since it is a chance to display lots of pointy teeth!

None of these theories has been definitely proven, and these are just the tip of the theoretical iceberg. Though some scientists are now claiming that yawning is a sign of sexual attraction rather than a desire to sleep, I’m not so sure.

We may never know exactly why we yawn or why dogs, monkeys and all other vertebrates—with the inexplicable exception of the giraffe—do it either. Perhaps giraffes do yawn, and we just haven’t (or can’t!) observe it. And perhaps humans yawn for different reasons at different times. A combination of events might trigger a yawn.

But back to the first question I posed: how many times do we yawn in a lifetime? Answer: approximately 240,000 times!

The concept of the erotic yawn emerged after many sexologists said they were consulted by people who yawned during sex. I’ve heard about excessive yawning during exercise and even during pregnancy, but not during sex.

For fun, you can view some pretty impressive pictures of animals yawning on sites like Google.

Want to know more? Well, if you’re really curious, then I suggest you plan to attend the International Conference on Yawning next year. The inaugural conference was held this year. In the meantime, enjoy your yawns —whatever they may signify. 

Sweet Dreams,

Michael J. Breus, PhD

The Sleep Doctor™


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