Yawning

Why do we yawn?

Researchers debate the purpose of yawning, and there’s no clear consensus. Currently, there are three main theories:

• To “wake up” your brain: The arousal hypothesis states that yawning activates your brain. This theory is tied to the fact that tiredness and boredom tend to trigger yawning the most. Boredom happens when the main source of stimulation in your environment is no longer able to keep your attention. This triggers drowsiness by stimulating your body’s sleep-signaling system. Researchers think that at this moment, your body must make an effort to maintain contact with your external environment. So, your body uses yawning to keep yourself awake. When you yawn, your heart rate increases. This may help you stay alert. Several of your facial muscles tense and stretch during a yawn, which may also help wake you up.
• To cool down your brain: The brain-cooling hypothesis suggests that brain temperature decreases with yawning due to the intake of excess air and changes in facial blood flow. Studies in both animals and humans show that yawning occurs before, during and after instances of abnormal thermoregulation, like heat stress and hyperthermia (high body temperature).
• To relate to others: The communication hypothesis is based on the contagiousness of yawning. Researchers who support this theory think that yawning functions as a communication or group synchronization function. They think it might serve to signal boredom or feelings of stress to others around you. Most researchers think social interaction is a minor function of yawning that coexists with a more significant function.

For several years, the main theory was that yawning brings in more oxygen — mainly for your brain. More recently, researchers discarded this theory, as studies revealed that a controlled lack of oxygen doesn’t result in more yawning than usual. In addition, this theory doesn’t explain why a fetus yawns, as a fetus gets oxygen through blood via its umbilical cord.

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For the time being, yawning remains a mystery. This is because yawning has complex mechanical, biological, neurological and behavioral influences. It’s hard to know where one influence ends and the next begins. In addition, researchers haven’t studied yawning nearly as much as other human behaviors and functions.

What triggers yawning

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Evidence suggests that tiredness is the most common trigger of yawning. Other triggers include:

• Waking up. It’s common to stretch and yawn at the same time when you wake up.
• Boredom.
• Certain stressful events. For example, athletes tend to yawn before a game.
• Imitating a yawn (which triggers a “real” yawn).
• Hunger.
• Seeing or hearing a yawn.
• Reading or thinking about yawning.

Why are yawns contagious?

In humans and certain social animals, seeing or hearing another yawn can trigger yawning. Researchers call this contagious yawning. And it’s usually difficult to suppress. Once again, researchers don’t know for sure why this happens. But they think it’s related to empathy — our ability to understand and share the feelings of another.

Studies show that the susceptibility to contagious yawning correlates with empathic skills in neurotypical people. In other words, the more empathic a person is, the more likely they are to experience contagious yawning. In addition, several studies have revealed that the susceptibility to contagious yawning decreases in neurodivergent people who have difficulty with social interactions. This typically includes people with autism spectrum disorder.

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Research also shows that we’re much more likely to have contagious yawning when we see or hear a close loved one yawn as opposed to a stranger. This also suggests a strong empathetic influence.

Contagious yawning may fit into what psychologists call mirroring (limbic synchrony) — subconsciously copying the body language, behavior, speech and facial expressions of people we’re emotionally close to. Psychologists think it’s a nonverbal way to show empathy.

How do we yawn?

Yawning involves a complex coordination of several muscles in your chest, throat and face. Physical steps of yawning include:

1. Your diaphragm (a muscular structure that helps you breathe) and rib muscles (intercostal muscles) contract. This causes you to breathe in air.
2. Your lower jaw (mandible) opens, making a “gaping” of your mouth. It’s possible to yawn without completely opening your mouth. But these yawns aren’t usually as “full” or satisfying.
3. The tip of your tongue retracts and moves downward. In addition, your larynx (voice box) and a bone in your neck above your larynx (hyoid bone) significantly move downward with the help of certain contracting muscles.
4. After this, the rate at which you’re breathing in air accelerates. Your soft palate (the back of the roof of your mouth) and part of your pharynx rise. This is when you may hear an inhaling sound. Your ears may also pop due to the opening of your eustachian tubes.
5. At this point, your pharynx’s diameter has increased three to four times its normal size. And your hyoid bone is as close to your lower jaw as it can be.
6. Peak forces of certain muscles cause your jaw and pharyngeal muscles to stretch as much as possible. This is when you may stretch other muscles in your body, like your arms. This is also known as the stretch-yawning syndrome or pandiculation. You might also make a facial grimace, have closed eyes and/or have watery eyes.
7. After this most intense point (climax) of the yawn, your muscle tension releases, and you exhale. Many people let out a sound or vocalization at this point. You may also feel a rewarding sensation.

Scientists think neurotransmitters in your hypothalamus (a part of your brain) play a role in kicking off the yawning process. Yawns are also associated with increased levels of neurotransmitters, neuropeptide proteins and certain hormones.

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