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Don't Know What Causes a Yawn? See What These Theories Have to Say

What Causes a Yawn?
Yawning is a reflex action, which causes us to open our mouth wide and inhale a large amount of air, which is then followed by its exhalation. Though yawning is more commonly associated with boredom, fatigue, sleepiness, overwork or stress, many of us also yawn when we wake up or simply when we see others yawn.
Chandramita Bora
Last Updated: Apr 9, 2018
Did You Know?
We start yawning even before our birth. Fetuses have been found to yawn frequently during the second and third trimester of pregnancy.
What causes a yawn is still a mystery. Though there are a number of different theories for explaining the possible reasons behind yawning, the scientific community is yet to arrive at a consensus. Many are of the opinion that yawning may be triggered by the interplay of multiple factors, and not by a single factor.
Possible Reasons Behind Yawning
Theory 1
The first theory about yawning is that it is induced when the concentration of oxygen in the blood and lungs decreases, while that of carbon dioxide increases. A yawn can help the body to take in more air, for which yawning was believed to indicate that the body is not getting enough oxygen.
However, a study conducted by Robert Provine, a developmental neuroscientist and Professor of Psychology at the University of Maryland, Baltimore County, found that neither increasing the concentration of oxygen, nor reducing the amount of carbon dioxide in the subject's environment stopped yawning.
Theory 2
Another supposition about yawning is that it is caused by a desire to stretch, as the very act of yawning involves stretching of several overused muscles of the body, such as the muscles used for breathing, swallowing, and speaking. So, yawning may help us stay alert, especially after relaxing for a period of time. This may be the case when we yawn after waking up, or simply when we are bored.
Theory 3
A recent theory has suggested that yawning may be a mechanism that helps cool down the brain. A study conducted in 2007 observed that people tend to yawn in situations, where the brain is likely to be warmer. This may explain why people tend to yawn more when they are tired or when they have not had enough sleep, as both conditions have been found to increase the temperature of the brain. A similar hypothesis is that yawning helps regulate the body temperature.
Theory 4
When we feel sleepy or tired, our breathing slows down, which hinders the supply of blood to the brain. Yawning allows us to inhale a lot of air, which improves blood circulation to the brain and reduces brain temperature. As the brain's temperature reduces, we can think more clearly and thus, yawning can help us stay alert.
It has also been observed in a study conducted by the State University of New York, that yawning reduces when the surrounding temperature is more than the normal body temperature.
The hypothesis that yawning has a cooling effect on the brain is supported by another experiment, which showed that nasal breathing can help reduce yawning, as against mouth breathing. This is because, when we breathe through the nose, oxygen can reach the brain faster, as compared to mouth breathing.
Theory 5
Some people believe that a yawn helps stabilize the pressure on either side of the eardrums. When we yawn, our mouth opens wide and the eardrums get stretched. This facilitates the release of excess pressure from the eardrums. This is the reason why, yawning is believed to be induced when the pressure inside our eardrums increases.
Theory 6
Another assumption regarding yawning is that it is caused by some chemicals found in the brain, like serotonin, dopamine, glutamine, glutamic acid, and nitric oxide. These chemicals are also responsible for affecting emotions, mood, appetite, and certain other phenomena. Activation of these chemicals in the brain is found to increase the frequency of yawns, while some other chemicals, such as opioid neurotransmitters, e.g., endorphins, can reduce yawning.
Theory 7
Yawning is believed to be induced when the level of glucose supplied to the brain decreases, as in the state of hunger.
Young couple yawning
Is Yawning Contagious?
A yawn is contagious, in the sense that it can easily spread to the person who is observing the other person yawning. Besides observing, even reading or thinking about it is also found to stimulate yawning in many individuals.
~ Some are of the opinion that contagious yawning may be caused by mirror neurons present in the frontal cortex of the brain, which imitates the action of others. These neurons get activated when exposed to a stimulus or action, performed by another individual, usually from the same species.
~ Contagious yawning is considered to be a herd instinct used to communicate tiredness and time to sleep, to other members of a group. It is believed that yawning could be a mechanism to signal other members of a group to stay alert, while contagious yawning could be a instinctual reaction to this, which eventually triggers a chain of yawning to establish group alertness.
~ One supposition is that the contagious yawn is a way of showing empathy to other members of a group. This may help explain why contagious yawning is observed within the members of the same species.
Yawning in Animals
~ Most of the vertebrates, including mammals and even birds yawn. It has been widely observed among primates, who use it as a threat gesture, by revealing their canine teeth. This is known as 'display yawning', in which case, the animal that yawns keeps its eyes open, in an attempt to see the effect of the yawning on others. Further, studies carried out in two species of primates, stump-tailed macaques and chimpanzees, have observed that both the species exhibit contagious yawning.
~ One theory is that yawning increases the hearing ability, by stretching the eardrums. This helps sleeping animals listen even the quieter sounds and thereby detect an approaching predator.
Interesting Beliefs
~ To the ancient Greeks and Mayans, yawning was a sign, which indicated that the soul of the person yawning was trying to run away from the body.
~ A common belief is that one should always cover the mouth while yawning, otherwise the soul may escape from the body. This belief may have originated to discourage public yawning, and also to maintain public health, as yawning might facilitate the spread of diseases
So, contrary to the popular belief that yawning indicates sleepiness, this natural process can actually help us stay alert by arousing the brain. However, excessive yawning can be associated with certain health problems as well. Hence, if you are experiencing excessive yawning, then consult a doctor and get the cause diagnosed.

Disclaimer: This article is for informative purposes only, and should not be treated as a substitute for professional medical advice.