For the longest time, the act of yawning puzzled medical researchers. Yawning seems commonplace and insignificant – you feel tired, you yawn. You see somebody else yawn, you yawn. You get bored, you yawn.
The problem researchers faced was how to tie these circumstances together and figure out a definitive biological purpose for yawning. When they did, they discovered that every yawn actually helps the brain function better and remain more alert. Here’s the surprising research.
Researchers in Switzerland found that yawning forms part of what’s called the “thermoregulatory” system of the brain. It’s controlled by a part of the brain called the hypothalamus, which regulates body temperature.1 So, say researchers, a basic function of yawning is to lower the temperature of brain tissue.
Your Brain’s Air Conditioner
One of the first clues about the brain-cooling function of yawns was the fact that in spring, as temperatures warm, people tend to yawn more. But then, as the body adjusts to the warmer temperatures, our yawning rate goes down.
Another clue is the discovery that brain tissue is consistently warmer than the blood flowing through the body. And when you yawn, as the muscles of the jaw open your mouth and contract, extra amounts of cooling blood course through your head – like the coolant that flows through a car engine to keep it from over-heating.
Plus, your sinuses also flex during a yawn. That allows for more cooling through the thin walls of the sinus as extra, cooler air, enters your head.2 So, in the same way that a cool breeze blowing across your face when you’re tired can help you stay more awake when you’re fatigued, the cooling action of a yawn, through a similar effect, can also boost your alertness.
Along with its cooling action, researchers in Switzerland say that a yawn and the muscular contractions that go with it also boost circulation of the cerebrospinal fluid. That increased flow helps to clear the brain of natural chemicals such as adenosine (a neurotransmitter) and prostaglandin D(2) (a hormone), that are linked to sleepiness.3
Catching a Case of the Yawns
As you’ve probably noticed, the act of yawning is contagious. If you see somebody else yawn, you’re more likely to yawn. However, research in Italy demonstrates that not all yawns are equally contagious. Perhaps not surprisingly, the yawns of your closest family and friends are more catching than the yawns of strangers.4
Along with that, men’s yawns elicit the yawns of other people more than female yawns, while women are generally more likely to start yawning when other people yawn than men are.
Researchers have also found that the bigger your brain, the longer your yawns. More brain tissue means you have more brain cells that need cooling – kind of like the way a large limo or SUV needs a bigger cooling system than a tiny Smartcar.
Interestingly, this also holds true for animals. A study on dogs shows that dogs with bigger heads and brains yawn for longer periods of time than small dogs with smaller heads.
One final yawning tip: If you’re in an important meeting and you’re trying to fend off the impolite urge to yawn, make sure to keep breathing through your nose. Air taken in through your nostrils and sinuses will cool your brain more than air that enters through your mouth and may make it easier to resist a yawn.6