Why does yawning occur and why does it seem contagious?

What is yawning?

Yawning is an involuntary action that involves opening the mouth widely while inhaling.  Yawning causes muscles of the face, head and neck to contract while other muscles stretch and relax.  Yawning can also be accompanied by a whole-of-body stretch involving the trunk and limbs.

Yawning is often associated with the time before going to bed and when waking up; and can occur when feeling bored, tired, stressed or over-worked.  Yawning can also occur when a person sees or hears another person yawning, giving it an “infectious” or “contagious” quality!

Humans however are not the only ones to yawn.  Research shows that animals yawn too, including primates, fish, guinea pigs, snakes, dogs, cats and birds!  Studies show that a dog watching its owner yawn can trigger the dog to yawn too!

So why do humans and animals yawn?

What causes yawning?

Despite our curiosity as to the cause of yawning, the precise answer remains somewhat elusive.  Over the years studies have attempted to explain this phenomenon with some interesting findings, which are outlined below:

1. Is yawning caused by a need for more oxygen?  It was once thought that yawning occurred for the purpose of inhaling more oxygen however the results of a study published in 1987 cast doubt over that theory.  That study found that people who inhaled more oxygen (to increase their blood oxygen levels) did not yawn less!
2. Is yawning caused by a need to exhale more carbon dioxide?  It was also thought that yawning may occur for the purpose of exhaling more carbon dioxide however the 1987 study mentioned above tested that theory too and found that inhaling more carbon dioxide (to increase blood carbon dioxide levels) did not increase yawning (as one might have expected).  So, if yawning is not principally about inhaling more oxygen or exhaling more carbon dioxide, what else could explain this phenomenon?
3. Is yawning designed to cool down the brain?   More recent studies published in 2011 and 2014 have revealed that when we are tired or have not had enough sleep, our brain temperature increases.  It was found that yawning has a cooling effect on the body and brain and may play a role in the body's thermoregulatory mechanisms to improve mental alertness and mental efficiency.  The studies also found that yawning was less likely to occur when the surrounding air temperature was higher than a person’s internal temperature (i.e. greater than 37 degrees Celsius) presumably because the external air would not have a cooling effect on the brain; and a person was less likely to yawn in extremely cold conditions because it may not be necessary or could have adverse effects.
4. Is yawning a way of stimulating the brain?  Yawning increases the heart rate, which typically increases cardiac output, which may improve blood flow and glucose supply to the brain, which is vital for brain function.  You can detect this increase in heart rate by monitoring your pulse rate when yawning.  Try it.  Yawning also involves contracting and stretching muscles of the face, head and neck.  Try that as well.   Contracting and stretching muscles helps improve lymph flow, especially if circulation is sluggish.  Yawning can also be accompanied by a whole-of-body stretch involving the trunk and limbs.   Doesn’t a yawn feel so much more satisfying when you yawn and stretch the whole body at the same time?  Give it a go!   Could yawning (with or without a whole-of-body stretch) form part of a reflex mechanism to give a little boost to our circulation, enhancing blood and lymph flow (in addition to cooling the brain)?  We may have to await further research for a definitive answer on this but in the meantime, here are some other interesting points about the things that can influence our tendency to yawn...

Other yawning influences and associations

• Chemicals in the brain such as endorphins, serotonin, glutamic acid, dopamine and nitric oxide can influence the frequency of yawning.  For example, it has been observed that “feel good” endorphins decrease yawning.
• Some medications can influence the frequency of yawning for example it has been observed that selective serotonin reuptake inhibitors (SSRIs) increase yawning.  SSRIs are typically used in the treatment of depression and anxiety.
• Yawning can also help stabilize pressure on either side of the ear drums.  When flying (e.g. in an aeroplane), do you sometimes open your mouth to help relieve pressure in the ears?  Yawning has a similar effect!

The reason why we yawn may not come down to one single factor but may occur for different reasons depending on the circumstances.  Next time you yawn, you might like to cast your mind back to these possible explanations and consider which one seems plausible in the circumstances.  As a general guide, if it is close to bedtime and you are yawning, you might like to take that as a cue to close your eyes and go to sleep.  If on the other hand you are yawning and need to stay awake (for whatever reason), perhaps that is a cue, the season and time of day), OR you might consider some time-out for a Yoganap (a restorative yoga class) to rest and rejuvenate your whole being before re-engaging with the world feeling revivified!

What makes yawning “infectious” or “contagious”?

When a person yawns, this can trigger another person to yawn.  This “infectious” or “contagious” quality of yawning seems to have its origin in the fact that humans have the capacity to empathise with (or relate to) one another.  Yawns are most contagious among people who are genetically or emotionally close, although yawning can also be triggered by simply hearing someone else yawn or seeing a picture of someone yawning.  Yawning appears to activate the mirror neurons in the frontal cortex of the brain, which are involved in mimicry or imitating the actions of others.  Therefore when a person sees or hears another person yawning, these neurons are activated and trigger the yawn reflex.  The yawn reflex can also be triggered between species.  For example, the yaw reflex in a dog can be triggered when the dog sees his human “friend” yawn!

This “contagious” yawning phenomenon is not peculiar to humans and their canine friends, but occurs in other species too.  Contagious yawning can influence an entire group or herd of animals, which is thought to communicate a need to sleep or conversely a need to stay "on alert" for predators or prey!

Can yawning be a sign of disease?

If you experience unexplained, excessive yawning and excessive daytime sleepiness, it is recommended that you consult your GP to explore possible medical causes.  For example, excessive yawning and daytime sleepiness can be associated with: 

• Heart conditions e.g. heart attack;
• Brain conditions e.g. brain tumour, stroke;
• Medications e.g. selective serotonin re-uptake inhibitors (SSRIs).

Listed below are questions that you can explore with your GP:

• When did the excessive yawning begin?
• Is it related to use of medicines?
• What medicines are you taking?
• How many times do you yawn per hour or day?
• Is it worse in the morning, after lunch, or during exercise?
• Is it worse in certain areas or certain rooms?
• Does yawning interfere with normal activities?
• Is the increased yawning related to the amount of sleep you get?
• Is it related to activity level?
• Is it related to boredom?
• What helps it?
• Does rest help?
• What other symptoms are present?

If you have any questions about this subject, please ask!  You can email email/tina)(thebreathingclinic.com or call 0488 040 242.