The surprising details behind yawning
I recently realized that in all my years of writing about sleep, I don’t think I’ve ever written about yawning. It’s time to fix that!
We all yawn, and we all see other people yawn everyday—your child at the breakfast table, your co-worker at a meeting, your partner at the end of the day while you’re doing the dishes together. But most people rarely give yawning much thought, other than it is embarrassing and annoying. When was the last time you thought about what that yawn means, or why it’s happening?
Yawning gets a bad rap. It’s an act that is often considered rude. That’s why your co-worker in that meeting tries to stifle her yawn, and why you might feel a flash of irritation when your spouse yawns in the middle of your run-down of your day, while you’re doing the dishes together. Though yawning can indicate boredom, there’s good reason to give your partner a break on this one. There are many reasons we yawn—and it’s really beyond our control. There’s a lot more to yawning than most of us know, so let’s take a closer look.
What is a yawn?
At a basic physiological level, a yawn is a big intake of air to the lungs. The mouth and jaw open wide. Through the mouth and nose, there’s a deep inhale followed by a slow exhale. Sometimes, people close their eyes when they yawn. Often, people stretch their arms or legs while yawning. We yawn most frequently in the first hour or so after waking, and the last hour or so before we go to sleep.
It may often be socially inconvenient, but yawning feels relaxing and even soothing. We have the ability to yawn throughout our entire lives, from infanthood to old age. Babies in utero even yawn. We’re not the only species that yawn. Nearly all vertebrates, from fish to reptiles to primates, exhibit yawning.
Yawning is an involuntary act—we don’t decide whether to yawn, we just yawn. As we all know, stopping a yawn is tough to do, even when a yawn is embarrassing or socially awkward.
What causes yawning?
Most people think of yawning almost exclusively as a sign of sleepiness and boredom. Sometimes, sleepiness and boredom are why we yawn. But as scientists have turned more attention to yawning, we’ve discovered that there are many other possible reasons for this common behavior.
Cooling the brain. There’s been a lot of recent interest in this theory of yawning, which suggests that yawning is a way the body regulates brain temperature. Regulating brain temperature keeps the brain working effectively, and lowering brain temperature helps stimulate alertness, supporting attentiveness, vigilance and other cognitive functions. Temperature regulation might be why we yawn most often first thing in the morning and at the end of the day. Temperature changes in the body are an important part of transitioning between sleep and wakefulness.
Research shows brain temperature does fall after yawning—and that yawning happens less often in colder temperatures than warmer ones. (So, less yawning on a chilly winter day than a steamy summer one.) Yawning triggers blood flow to the brain and its surrounding areas of the head, neck, and face, which pulls heat from the skull.
Do your eyes ever tear up when you yawn? It’s a common reaction, and scientists think it may be related to the cooling effect of yawning on the brain.
Transitioning through different states of energy and alertness. Our bodies change states of energy, vigilance, and alertness throughout the day, according to a number of factors, including:
• Time of day
• Activity and exertion
• Amount and quality of sleep
• Shifting hormones
• External circumstances and environment
Yawning may be a way the body both signals and influences transitions from one state to another. For example:
• A yawn in the morning may be a sign of transition from sleep to wakeful attentiveness, and a yawn at night may mark the body’s transition back to sleep.
• A yawn in the midst of a tedious or repetitive activity may indicate the brain transitioning to a lower level of attentiveness and may also be the brain’s attempt to boost alertness and engagement.
• Yawning after exercise or physical exertion is pretty common. That post-exercise yawn may be a way the body redirects blood flow to the brain from its major muscle groups—and it may also be a way the body cools the brain after heating up through exertion.
• Have you ever found yourself yawning before a stressful event—a job interview, a solo in your choir, a first date? There’s a relationship between yawning and stress that scientists don’t yet fully understand. Yawning may be a signal of a shift from a relaxed state to an anxious, vigilant one.
Social messaging. Yawning is an ancient behavior among humans, other mammals, and most vertebrates. Yawning has long been considered by many scientists to be a form of communication that evolved before humans had spoken language. We may yawn to signal tiredness, boredom, stress, hunger, or any number of messages.
Why is yawning contagious?
You’ve probably has the experience of yawning after seeing someone else do it, or having someone yawn in response to you. Maybe you’ve yawned while reading this article. (I will admit, I did when I was writing it!) Yawning is contagious, and we’re highly suggestible to yawning.
Yawning is believed to be a sign of empathy among humans. Empathy—the ability to recognize, understand, and share the feelings of others—is an important part of our social interactions. Just as we’re apt to laugh when we see others laughing, or show concern and fear when we see others upset or afraid, we respond with a yawn when we see others yawning—especially people we feel close to. Research shows we’re more likely to experience contagious yawning with our families and our friends, compared to strangers. Even though yawning happens in utero, contagious yawning doesn’t start until around the age of 5—another sign this phenomenon is linked to our ability to empathize, which develops in early childhood. There’s also evidence that contagious yawning is less likely to take place in people who have conditions that affect social interactions, including schizophrenia and autism spectrum disorder.
We’re not the only species to experience contagious yawning. Chimpanzees and other primates—highly social mammals—yawn contagiously as well. Domestic dogs also exhibit contagious yawning. Dog owners, do you feel like your pup is part of the family? Science suggests that our dogs yawn contagiously in response to human yawns.
Why you should pay attention to yawning
Most of the time, yawning is part of the body’s normal functioning. There are health conditions for which excessive yawning is a symptom, including:
• Stress and anxiety
• Head trauma
• Multiple sclerosis
• Sleep disorders, including sleep apnea and insomnia
• Side effects from SSRI medications used to treat depression
• Reaction of the vagus nerve, which may be a sign of heart problems or other conditions
If you experience excessive yawning, don’t ignore it. Speak with your physician or seek medical attention promptly.
Want to stop yawning?
Looking for some help avoiding those embarrassing yawns that happen at the worst times? Follow these tips, and remember the key is to keep things cool:
Don’t let your environment get too warm. Yawning is about cooling things down internally—specifically the brain. Spending time in a warm environment will make you more likely to yawn.
Drink some ice water. Worried about yawning in the middle of a meeting? Keep a cold drink within arm’s reach and take a sip if you feel a yawn coming on.
Use a cold compress on your forehead. Scientists have found that cooling the forehead can lower brain temperature and stop excessive yawning.
There’s a lot more to learn about yawning, and it seems likely that yawning serves more than one purpose. Yawning seems likely to have a brain cooling function, and a social function as well—albeit one that’s less useful than it might have been for our ancient ancestors!
Michael J. Breus, PhD
The Sleep Doctor™