The Science of Yawning: Why Do We Yawn and What Does It Mean?

One of the most infectious responses that we emulate from other people (other than laughing) is yawning. Did you let out a yawn while reading this sentence? You just exhibited an uncontrollable and pretty common human behavioural response! 

What is yawning?

Yawning is the involuntary action that makes our jaw go wide and the exhalation of the deep breath we take in while our mouth is open. Yawns are more likely to occur in moments of tediousness or drowsiness. If you see, hear, think about, or even read about it, it will trigger an urge to yawn.

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Evolutionary perspective

• Charles Darwin noted in 1838 that yawning is an early and universal behaviour. He observed that watching a dog, a horse, and a man yawn made him feel that all animals are built on the same structure.
• In some early vertebrates, yawning could have been one of the ways the body prepares for any kind of physical labour. This could explain the evolution of yawns as a way of stimulating muscle function and being ready for physical exertion.

Why do we yawn?

Remaining as one of the most unresolved mysteries of human life for many centuries and even in the current era, yawning continues to elude researchers from figuring out the exact reasoning behind it. Let’s dive into the various theories related to yawning:

1. Breathing Regulation

An old and popular theory suggests yawning can increase oxygen intake and in turn expel carbon dioxide build-up. This hypothesis suggests that it helps to regulate oxygen levels in the body, especially when drained or bored. As the research has not been consistent in showing the link between yawning and oxygen levels, this idea is fairly controversial.

2. States of Awareness

Another theory says that yawning is a mechanism that aids the brain in switching between different states of awareness. For example, it might transition from boredom to alertness or to exhaustion, and signal the brain to nudge the body towards sleep or vigilance based on requirement. These transition signals could prepare the brain for any change happening in the surrounding environment and respond to external stimuli accordingly. When we yawn, blood flow to the brain increases, helping regulate our state of alertness for the next action.

3. Thermoregulation

Just like how sweating cools the body, yawning can reduce the brain’s temperature and also improve cognitive functions. This theory is reinforced by the fact that people yawn more when they’re exhausted or in warm settings.

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Neurochemical Regulation

Yawning is a behaviour linked with the balance of neurochemicals that modulate various parts of the brain and regulate different body processes, including muscle relaxation, pain, pleasure and sleep. The major neurotransmitters that are connected to yawning are dopamine, serotonin, acetylcholine, oxytocin, endorphins, etc.

• For example, dopamine is a neurotransmitter that plays a major role in initiating yawning. When dopamine levels drop, there may be increased yawning, and when the levels rise, the tendency to yawn is reduced.
• Selective serotonin reuptake inhibitors (SSRIs) are psychiatric drugs used to treat depression and mood regulation by increasing serotonin levels, and this drug might affect the frequency of yawns.
• Oxytocin known as the love hormone stimulates social connection, love and relaxation. Its role in social bonding could be associated with contagious yawning, where people yawn when they see or hear others yawn. 
• The neurochemical endorphins generally associated with stress relief and pain relief when we eat, exercise or do other pleasurable activities can also influence yawning to manage arousal and stress levels. 
• These hormones and neurotransmitters coordinate in various areas of the brain to govern when and how we yawn.

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Muscle Activation and Circadian Rhythm

When you yawn, you would have noticed how your body muscles stretch along with your jaw, to relieve tension or body pain. Studies state that yawns can promote circulation, relax the facial muscles and increase preparedness, and are similar to stretching before exercise.

Our natural circadian rhythm (the internal clock that controls the activities of the body for the entire day) is closely linked to the frequency of yawns. The distribution of yawns can reveal an individual’s sleep-wake cycle.

When we have jetlag irregular sleep patterns or night shift work, our circadian rhythm is disrupted and this can result in abnormal patterns of yawning. During travel between time zones, we might yawn more as our body has to adjust to a different sleep pattern. This happens because the circadian rhythm and our sleep-wake cycle are affected by travel.

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Social and Emotional Bonding

We are more likely to mirror a yawn from someone we feel emotionally connected to (a friend significant other or family). Mimicking behaviours in both humans and other species are associated with empathy and social bonding. Highly empathetic individuals tend to yawn more when they see others yawning, supporting the theory that yawning has social and emotional functions.

Mental Health 

While yawning is observed as a physical behaviour, it is also connected to mental health especially conditions like anxiety, depression and sleep disorders. For example, people with depression have been observed to yawn excessively suggesting that it could be a symptom of this mental disorder. To cope with the lack of rest and extreme stimulation, yawning might be induced by the brain. 

When we are extremely tired or haven’t been sleeping enough we might yawn frequently as our brain tries to cope with the lack of rest or overstimulation. People who have sleep disorders, like narcolepsy, sleep apnea and insomnia may experience excessive yawning as their sleep is usually disrupted by these disorders. 

The vagus nerve (part of our parasympathetic nervous system) regulates digestion, heart rate and breathing rate. Studies suggest that when the vagus nerve activates, yawning occurs as a response to it due to changes in brain chemistry or factors like stress or trauma.

During somatic therapy or other therapy approaches that help to process trauma, yawning is observed and indicates the release of trauma stored in our body. Yawning could be the physical relief or release that our body needs after processing complex emotions, memories or intense experiences.

Yawning can be a sign of a mental shift when dissociation or disconnect from a person’s body or surroundings occurs. People experiencing dissociation, predominantly those with a history of trauma, may yawn a lot and this could be their body’s attempt to reconnect to themselves. As the act of yawning promotes relaxation, it can balance the effects of stress and anxiety.

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Yawning across species

Have you watched those YouTube videos of cats or dogs that yawn so cutely? We’re not the only ones who yawn and it has been perceived in several other species of the animal kingdom. Some of the research regarding yawning in other species has suggested that:

• Dogs might yawn in some social conditions, as a sign of empathy or stress that they exhibit with their human or dog companions. Research suggests that dogs may observe their owner yawning and follow suit. As dogs tend to mimic the emotional states of their caretakers, it could serve as a bonding function. Too much yawning in dogs can indicate high levels of discomfort pain stress or other underlying health issues.

• Yawning could serve the function of communication among animals that have complex group dynamics such as apes. For example, when a chimpanzee in a group is exhausted or stressed, contagious yawning can occur to signify the need to rest or become more alert. For some specific non-human primates, yawning peaks can occur before and after sleep, during the day. 

• Research done on lions in the Makalali Reserve (South Africa) found that lions yawn when they are lazing around and then rub their heads with each other in an affectionate gesture. Yawns can also be a mode of communication for lions to signify that it’s time to be alert and move. 
• It’s not just the big cats that display this open-mouthed gesture; House cats also do the same. If a cat yawns when you pet it, this could be a sign they feel comfortable and relaxed. On the other hand, cats might yawn when they anticipate something exciting, like playtime, or when they are stressed.

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Did you know?

• Exercising, staying hydrated and having a regular sleep schedule can reduce the frequency of yawning. Despite maintaining your efforts if you find yourself yawning excessively, it might be better to consult a doctor to check for underlying medical conditions.   
• Recent research in psychology and neuroscience suggests that yawns could improve the attentiveness of the person who observes us yawning, and the subsequent contagious yawns can enhance social cohesion or unity. 
• Yawns are universal and are not unique to humans. It has been observed in animals and birds such as cats, dogs, chimpanzees, ostriches, emus, and others.
• Frequent yawning occurring along with other symptoms of trauma, is our body’s effort to cope with emotional and biological stress.
• We are more likely to yawn when we are bored or engaged in activities like passive listening, watching TV, or driving.

How many times did you yawn while reading till here? Even reading about this topic can induce yawns! Just like some of the complexities surrounding the functions of our bodies, the debate about yawning continues to be wide open!