Everybody yawns, including adults, babies, and even animals. Scientists have proposed several hypotheses for what exactly causes this phenomenon.
Most people associate yawning with being tired or bored. Studies of other mammals, such as sea lions, have shown that they also yawn more frequently when they are resting or sleepy. Recent research suggests yawning may serve important physiological or social functions beyond simply showing that we are tired.
Why Do We Yawn?
Scientists have yet to reach a consensus on why we yawn. Some scientists argue that yawning serves a physiological function, such as helping the brain wake up or cool down. Others argue that yawning serves a psychosocial function, in enabling people to communicate that they are sleepy, bored, or stressed.
Theory #1: Yawning Wakes Up the Brain During Times of Boredom or Tiredness
One theory holds that yawning may help keep the brain awake during boring or passive activities.
The act of yawning forces the muscles in the face and neck to move. Researchers believe this movement may stimulate the carotid artery, leading to an increase in heart rate and the release of wake-promoting hormones. Experts theorize that yawning may also directly influence brain activity by prompting movements of brain fluid away from a resting network and into a more active state.
The electrical conductance of the skin also increases when yawning, similar to the effects of caffeine. Since caffeine promotes wakefulness, researchers surmise that the similar physiological response may indicate that both serve the same function.
Adding further evidence to this theory are the types of activities during which yawning is more likely to occur. For example, people are more likely to yawn when they are engaged in a more passive activity, like driving, watching television, or listening to a lecture. When they are doing something more active, such as cooking or talking, they are less likely to yawn.
Theory #2: Yawning Helps the Brain Cool Down
Yawning may aid in brain thermoregulation, or the process by which the brain maintains its core temperature. During a yawn, the facial muscles move and contract, increasing blood flow to the face where heat can dissipate more easily. Some people’s eyes tear up when they yawn, which may also release heat. Likewise, taking a deep breath of fresh air may help send cooler blood to the brain.
Although more research is needed, preliminary studies of humans and animals have provided evidence for the thermoregulation theory. For example, a study of parakeets found that they yawned more when the ambient temperature increased, especially as it neared their body temperature. In a study of humans, researchers placed either a warm pack or an ice pack on participants’ foreheads while they watched videos of people yawning. Those with a warm pack yawned more in response to the videos, while those with the ice pack yawned less.
Manipulating neck temperature was also shown to influence yawning in another study. Participants placed a warm, cool, or room-temperature pack against the carotid artery in the neck. They held it in place for five minutes, before removing it and watching a video of people yawning. Those who had the warm pack yawned 3 times more often than those with the cool pack.
Studies of seasonal changes in environmental temperature also provide support for the thermoregulation theory of yawning. For example, one study asked participants to self-report how many times they yawned during the winter and during the summer. The researchers found that participants were significantly more likely to report yawning during the warmer summer months. This correlation held up after taking other variables into consideration, such as humidity or sleep.
People with certain conditions that increase core body temperature — such as multiple sclerosis, anxiety, or stroke — may find yawning temporarily relieves their symptoms. These conditions often cause excessive yawning, which may be a natural response to overheating.
Theory #3: Contagious Yawning Is Linked to Empathy Skills
Most people agree that yawning is contagious. When people see or hear other people yawn, they tend to yawn themselves. Even reading or thinking about yawning can prompt a yawn.
The contagiousness of yawning suggests it may be an empathetic response that helps humans and other mammals communicate. Brain imaging reveals that the parts of the brain associated with empathy and social behavior show a spike in activity when a person watches someone yawn.
Research suggests that the closer someone feels to another person, the more likely they are to yawn when that person yawns. In other words, a person is more likely to yawn after seeing a friend or family member yawn than an acquaintance or stranger. While humans yawn as infants, they do not become susceptible to contagious yawning until they are around 4 to 5 years old, when they have developed the mental pathways to understand how other people are feeling.
According to some studies, contagious yawning relates to higher empathy scores. Conversely, disorders such as schizophrenia or autism spectrum disorder that interfere with social abilities also seem to reduce contagious yawning. People who score higher on selfishness, callousness, and other antisocial personality traits are also less likely to yawn in response to others’ yawns, although tiredness still seems to play a larger role.
The empathy theory of yawning has been studied in the animal world as well. Like humans, dogs only demonstrate contagious yawning once they have reached a stage of development where they can notice others and recognize their emotional state, around 7 months of age. However, unlike humans, how emotionally close a dog is with the yawning person does not affect their likelihood of yawning. This finding has led some researchers to question the theory that yawning is linked to empathy.
Other Theories About Why We Yawn
Yawning helps open your eustachian tubes, which connect your throat to your ear. This action can help relieve the uncomfortable pressure buildup that occurs when the ear does not have time to equalize, such as when a plane is landing. That said, since swallowing achieves the same purpose, scientists do not believe this is the primary reason we yawn.
An older theory posited that people yawn when they are not receiving enough oxygen to their brain. The idea was that yawning helped bring in fresh oxygen to the brain whenever there was more carbon dioxide than oxygen in the blood. Studies have shown that yawning does not increase when people breathe in more carbon dioxide, so scientists have moved away from this theory.
How Much Yawning Is Too Much?
There is no official consensus on how much yawning is too much, though some experts consider it abnormal to yawn more than three times within a 15-minute period if there is no obvious cause. The average person yawns up to 28 times per day, usually after waking up and before going to bed. Yawning in the absence of tiredness, boredom, contagion, or other typical cues is also considered abnormal and may indicate an underlying disorder.
Excessive yawning may be caused by damage to the parts of the brain involved in yawning. Too much yawning can be a sign of neurological conditions such as:
- Parkinson’s disease
- Multiple sclerosis
- Brain tumor or swelling
In rare cases, yawning can also be caused by certain drugs, including antidepressants, opioids, dopaminergic drugs, and benzodiazepines. People with sleep disorders like insomnia or obstructive sleep apnea are also more likely to experience excessive yawning.
When to Talk to Your Doctor About Yawning
It is common to yawn after seeing someone else yawn, or when you are feeling tired, bored, hungry, or stressed. If you are yawning more than usual and you are not sure why, talk to your doctor. You should also consult your doctor if you are yawning a lot due to sleeping poorly or feeling sleepy during the day. Your doctor will ask questions and order tests if appropriate to understand what is causing your yawning, and recommend next steps you can take.
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