Why Do We Yawn?

We’ve all yawned at various points in our lives — when we’re up past our bedtimes, zoning out in a lecture hall or on the plane to help clear our ears. But while yawning has long been associated with drowsiness or boredom, it’s not a reflex that’s been extensively studied.

In fact, according to a 2022 review, there is still no consensus on the primary function of yawning (1), though different hypotheses abound. There are, however, all kinds of theories, ranging from a brain-cooling mechanism to a way of jump-starting alertness. We spoke with Dr. Laura Purdy, a board-certified family medicine physician, and Dr. Kevin Huffman, a board-certified bariatric physician, for a little insight into why we yawn, including a look at the most popular theories.

Note: The content on Sleepopolis is meant to be informative in nature, but it shouldn’t be taken as medical advice, and it shouldn’t take the place of medical advice and supervision from a trained professional. If you feel you may be suffering from any sleep disorder or medical condition, please see your healthcare provider immediately.

Long Story Short

There are many theories about why we yawn, but at this time, there is no general consensus on its function.
Yawning often occurs during the transition between being awake and being asleep, which is why it’s often associated with sleepiness or boredom.
Yawning may be a way to increase oxygen to the brain as a method of increasing alertness.
Excessive yawning can also be associated with certain neurological disorders.

Sleepiness and Boredom

While yawning often happens when we’re waking up or nodding off, it may be associated with drowsiness and boredom in another way, too. “Yawning may act as a mechanism to increase oxygen intake during times of fatigue or boredom, helping to keep us awake and maintain cognitive function,” Huffman tells Sleepopolis.

In that case, instead of signaling that we’re drowsy or not engaged with whatever’s happening around us, yawning could be the brain’s way of jump-starting our system. “This theory is saying you yawn when you’re feeling sleepy and need to increase alertness or ‘wake up’ the brain,” explains Purdy.

As a Social Reaction

If you’ve ever yawned after seeing or hearing someone else do it, or even reading about it (in which case, it may have just happened!), you’re familiar with the idea of contagious yawning. According to research, it’s a well-documented phenomenon in humans, chimpanzees and, interestingly, dogs (2). Unfortunately, the “why” is still pretty unclear.

One theory is that contagious yawning is a kind of empathetic social behavior that serves as a sort of communication signal, similar to laughter. According to some research, the part of the brain associated with contagious yawning is also related to social understanding and social processing. Some studies found that those with higher empathy scores, which is determined by measuring facial expressions, gestures, and vocal responses to certain situations, are more likely to experience contagious yawning (2). One study also found that women were more susceptible (3).

To Cool Down the Brain

Yawning as a brain-cooling mechanism is another theory. The thought is that a reflexive yawn could be the brain’s way of bringing cool air into our system, which lowers the temperature of the blood flowing to the brain. “This cooling effect may enhance mental alertness and overall performance,” says Huffman.

More research is warranted, but some experts support this theory. Yawning is more likely when it’s hot outside, which is when the brain might benefit from a rush of cooling air. It could actually heat up the brain if the air temperature is warmer than your blood. So, when it is hot outside, yawns should happen less often since other cooling mechanisms, such as sweating, kick in (4).

Other Theories on Why We Yawn

Some theories about why we yawn overlap with others, like those relating to lung stretching and increased oxygen to the brain. “One theory is that when you yawn, you’re stretching the lungs and their tissues,” says Purdy. “This allows your body to also flex its muscles and joints. It may also increase blood flow toward your face and brain, which in turn increases alertness.”

Huffman adds that yawning could also play a role in resetting our respiratory systems. “When we’re tired, our breathing rate naturally slows down, and yawning provides a way to stretch and exercise the muscles involved in breathing,” he says. “This helps improve ventilation and boosts oxygen levels in the body.”

Is There Such Thing as Too Much Yawning?

According to Huffman, there’s no universal definition for the limit of yawning frequency. Adults tend to yawn about nine times per day, and it’s not uncommon to yawn two or three times in a row (1). Excessive yawning, however, can be cause for concern. “It may indicate underlying issues such as neurological conditions,” Huffman explains. These include:

Parkinson’s disease, epilepsy, and multiple sclerosis. Because these are conditions that affect the brain, they may trigger excessive yawning, which is described as more than three yawns in a 15-minute period without appropriate stimuli (5).
Stroke.

“It’s important to note that not all instances of excessive yawning are worrisome, as some individuals naturally have a higher baseline frequency,” says Huffman. “However, if someone experiences a sudden and unexplained increase in yawning frequency, especially without feeling tired, it would be advisable to consult with a healthcare professional for a thorough evaluation.”

That’s especially true if excessive yawning is becoming disruptive to your daily life, it interferes with your concentration, or you’re also experiencing other symptoms, like sudden changes to your alertness.

FAQs

Why do we stretch when we yawn?

Researchers don’t yet understand why we often stretch when we yawn. “One prevailing theory suggests that stretching helps increase blood flow to the brain and body, aiding in the process of becoming alert,” Huffman tells Sleepopolis. “It may also assist in redistributing cerebrospinal fluid, which plays a role in maintaining brain function.”

Is yawning contagious?

Research suggests that yawning is contagious in humans, primates and even dogs. It’s a well-documented phenomenon, but we have yet to determine why. (6) One theory is that contagious yawning is empathetic social behavior that operates as a kind of communication signal, similar to laughter.

The Last Word From Sleepopolis

While researchers continue to learn more about why we yawn, it’s clear that this reflex serves a greater purpose than just stretching our jaw and making our eyes water — even if we don’t quite understand it just yet. While a yawn may seem like a small thing, Huffman says its role in maintaining our physiological equilibrium shouldn’t be underestimated. “Without the ability to yawn, our bodies might struggle to regulate temperature and alertness, leading to increased fatigue, reduced cognitive function, and an overall decline in physical and mental performance,” he adds. Still, if you’re concerned that you’re yawning too much, make sure to speak with your doctor.

Sources

Purdy, Laura. Personal interview. September 2024.

Huffman, Kevin. Personal interview. September 2024.

Doelman CJ, Rijken JA. Yawning and airway physiology: a scoping review and novel hypothesis. Sleep Breath. 2022 Dec;26(4):1561-1572. doi: 10.1007/s11325-022-02565-7. Epub 2022 Feb 5. PMID: 35122606; PMCID: PMC9663362.
Franzen, A., Mader, S., & Winter, F. (2018). Contagious yawning, empathy, and their relation to prosocial behavior. Journal of Experimental Psychology: General, 147(12), 1950–1958. https://doi.org/10.1037/xge0000422
Chan MHM, Tseng CH. Yawning Detection Sensitivity and Yawning Contagion. Iperception. 2017 Aug 25;8(4):2041669517726797. doi: 10.1177/2041669517726797. Erratum in: Iperception. 2018 Feb 12;9(1):2041669518760868. PMID: 28890778; PMCID: PMC5574488.
Massen JJ, Dusch K, Eldakar OT, Gallup AC. A thermal window for yawning in humans: yawning as a brain cooling mechanism. Physiol Behav. 2014 May 10;130:145-8. doi: 10.1016/j.physbeh.2014.03.032. Epub 2014 Apr 12. PMID: 24721675
Teive HAG, Munhoz RP, Camargo CHF, Walusinski O. Yawning in neurology: a review. Arq Neuropsiquiatr. 2018 Jul;76(7):473-480. doi: 10.1590/0004-282X20180057. PMID: 30066799.
Gallup AC, Wozny S. Interspecific Contagious Yawning in Humans. Animals (Basel). 2022;12(15):1908. Published 2022 Jul 27. doi:10.3390/ani12151908