Few bodily quirks are more relatable than a yawn. We yawn after waking up, near bedtime, during a slow meeting or simply when we watch someone else do it. Most of the time, yawning accompanies an ordinary shift in alertness or signals that we need better sleep. But an unexpected string of yawns can also be puzzling or even alarming, especially when you know you're well-rested.
Yawning is “a complex reflex,” and the purpose or cause isn’t always clear, explains Panagis Galiatsatos, a pulmonologist at Johns Hopkins Medicine and author of "Medicine for the Greater Good."
Here’s why we yawn, its most common causes and when the reflex means you might want to schedule an appointment with a doctor or sleep specialist.
Why do we yawn?
Yawning is an involuntary reflex
in which your mouth opens wide, your jaw and throat stretch, and a deep inhalation is followed by a shorter exhalation, says Galiatsatos. He explains that the reflex engages “the muscles of the mouth, jaw and throat” along with the lungs, and happens to just about everyone.
It also happens more often throughout the day than many of us realize. Adrian Guggisberg, a clinical neuroscientist and head of neurorehabilitation at Geneva University Hospitals in Switzerland, notes that adults average roughly 10 to 20 yawns a day, though individual patterns vary considerably. “There is no strict ‘normal’ number,” he says.
Despite being so common, “there does not appear to be a ‘yawning center’ in the brain,” says Michael Brenner, a sleep medicine specialist and associate professor of head and neck surgery at the University of Michigan. Instead, he explains that networks in the brainstem and hypothalamus that help regulate sleep, wakefulness and body temperature all appear to be involved, alongside several brain chemicals that influence the reflex.
While yawning’s most common triggers are widely understood, doctors are less certain about what purpose the reflex serves. Many people assume yawning is meant to make us feel more awake or sleepy, depending on when we do it. But Guggisberg explains that across his research, while sleep pressure does increase the likelihood of spontaneous yawns, “yawning did actually not make the brain measurably more alert afterwards.”
Other experiments have found that people do not yawn more when oxygen levels are reduced or carbon-dioxide levels are increased, undermining the long-standing idea that yawning is a reflex designed to bring in more oxygen or clear excess carbon dioxide.
What causes yawning? Is it normal to yawn but not be tired?
Sleepiness remains the most common reason we yawn, as the reflex frequently occurs when we are transitioning between sleep and wakefulness or when poor-quality sleep leaves us less rested than we realize. “Fatigue is only one trigger,” Brenner says. He explains that yawning can also become more frequent during moments of boredom, prolonged concentration and even during ordinary shifts between different levels of alertness.
Seeing or hearing someone yawn can also trigger an automatic copied response. Meilan Han, a pulmonologist and chief of pulmonary and critical care medicine at the University of Michigan Health, explains that this form of contagious yawning appears to involve brain networks associated with “social behavior and empathy.”
Hunger may also trigger yawning, though scientists don’t know precisely why. Stress, anxiety and anticipation are common culprits as well, notes Brenner, as “yawning is well documented before performances, competitions, exams and other tense moments.” Though the connection is not fully understood, he notes that “animal studies trace this to stress-related pathways running from the amygdala to the hypothalamus.” In such situations, “yawning could be the body’s way of calming us down, though we are not certain,” Galiatsatos says.
Medications also deserve attention, adds Guggisberg, particularly when frequent yawning begins even though the medication does not make you feel sleepy. As examples, Brenner says yawning has been linked to taking certain antidepressants - especially selective serotonin reuptake inhibitors - as well as opioids, Parkinson’s medications, benzodiazepines, and drugs used to induce anesthesia.
“There is also a theory that yawning helps regulate brain temperature,” says Han, as some research has found that the reflex becomes more frequent as body or brain temperature rises. The theory suggests that the deep inhalation, facial stretching and changes in blood flow associated with a yawn may help cool the brain, but the evidence is not conclusive.
When is yawning a warning?
Yawning by itself usually isn’t a reason to worry. Brenner says concern increases when frequent yawning occurs alongside excessive daytime sleepiness, loud snoring, witnessed pauses in breathing or sleep that leaves you feeling unrefreshed.
Those clues may warrant an evaluation for a sleep disorder such as obstructive sleep apnea or narcolepsy, notes Han. A doctor or sleep specialist can review your sleep habits, assess your symptoms and recommend testing or treatment when appropriate, she adds.
You should also contact a clinician if your yawning “is accompanied by neurological symptoms such as a sudden weakness or numbness on one side, trouble speaking or swallowing, double vision, unsteadiness, confusion or fainting spells,” says Brenner. Such symptoms often require emergency evaluation because they can indicate a stroke. Yawning accompanied by chest pain, shortness of breath or lightheadedness also warrants prompt medical attention.
But most bouts of yawning, stresses Guggisberg, "are completely normal.”
This article originally appeared on USA TODAY: Can’t stop yawning? Here’s when it could signal a problem
