Why do we yawn? Science gives us the answer

We all know that we yawn when sleepy or tired, but have you ever wondered why we do it? We are going to discover what physiological function yawning fulfills.

Yawning is an involuntary mechanism through which we introduce a more significant amount of air into our lungs. Throughout our lives, we yawn around 250,000 times. There is still no clear and precise explanation for this phenomenon. It seems that the structures that control yawning are found in the brain stem, including the responsible neurotransmitters found in the nucleus of the hypothalamus. The hypothalamus is located in the brain, where we know that the nervous system is also controlled.

Yawning would then seem related to brain processes and structures, but in what way? We’ll attempt to provide an answer to this query in today’s essay by outlining all that is known about yawning and outlining the various hypotheses that have been proposed to comprehend it.


What is yawning?

Although it is commonly thought that yawning is a reflex, yawning is known in etiology as a “fixed pattern of action” this means that it is an instinctive response and not the response to a stimulus. Being a “fixed pattern of fixed action,” you cannot yawn just a little. That is, it has a certain intensity. Although we can indeed stop yawning if someone bothers us or interrupts us.

All yawns look alike. It is easy to recognize when a person is yawning. They open their mouth wide, tilting their head slightly backward, and squint their eyes that turn reddish (tears). In this process, you salivate and “open your ears” (the Eustachian tubes actually open). There are also many more cardiovascular, respiratory and neuromuscular actions that we are not aware of.

Although all yawns are practically the same, they can have different duration. Typically, they last between 8 and 10 seconds, but there can be yawns of three seconds or much more than 10. The intervals between pains (non-pathological) are estimated to be 68 seconds on average, and the frequency does not present any relationship with the duration.

Depending on the moment, we can associate yawning with different non-verbal messages. We yawn when we are tired, but also when we feel anxious, even sometimes when we are hungry or before starting something new. Yawning could be a psychological release after a period or moment of alertness or high stress. It can also express strong and not very acceptable emotions such as boredom, rejection, or anger, which is why we often cover our mouths to hide yawning. This is common in different cultures.

Bears, crocodiles, monkeys, iguanas, birds, turtles, fish, etc., are all animals that have a backbone and can yawn. Apparently, it could have to do with the degree of evolution of the species. Not all mammals yawn the same length.


What is the use of yawning?

We have seen that yawning is an instinctive act present in many species. They are very similar but have minor differences. From these data, several studies have attempted to determine the precise function of yawning.

  1. Oxygenate the blood

Popularly, it is thought that we yawn when there is a lack of oxygen in the blood. Yawning would be the way to bring more oxygen to the blood through breathing. The assumption seems quite reasonable. The more air, the more oxygen. Historically, this has also been the most widely accepted theory for the logic presented. The more cycles of breaths, the more oxygen in the blood and fewer CO₂.

Some studies have tried associating the detection of shortness of breath by the hypothalamus with yawning. However, there are still no conclusive results. Moreover, no relationship between blood oxygen and the number of yawns performed in any of the animals studied has been obtained.


  1. Cool our brain

In 2016, Oneonta University, New York, conducted a study that related the duration of yawns with the brain development of mammals. As we previously discussed, yawns vary in length over time, but why does this seem to be related to the size and density of the brain’s neurons? Yawning would be a process by which we cool the different brain structures. It would be like a ventilation system. When we yawn, we introduce cold air into our noses and mouth. This process can cool the blood by increasing blood flow to the brain.

Differences in yawn duration in animals with larger brains may be due to enhanced cognitive abilities and a more excellent range of behaviors. According to Professor Andrew Gallup, leader of the American study, the duration of yawns has an undeniable relationship with the complexity and size of the brain, the parameter that most influences this being the number of neurons in the mammals studied.

Mice have about 4,500 neurons, and their yawns last about two seconds. Humans have 2.2 times more neurons, and our yawns last 3 times longer, 6 seconds per 10,000 neurons. The most intricate structure is the human brain. It processes all the information from our senses, gives a coordinated response, and simultaneously maintains all our vital functions. Therefore, it shouldn’t get hot. It is not yet known, but it is believed that the consequences of yawning affect all regions and areas of the brain.

As a result of these conclusions, another study carried out at the University of Vienna wanted to relate temperature and yawning to deepen and confirm the theory of refrigeration. These results were compared with those of another study carried out in Arizona. The idea was simple, if yawning serves to cool the brain, there is little point in yawning when the outside temperature is very high.

The results showed temperature differences, showing an increase in summer yawning in Vienna and a decrease in Arizona. Although they may seem opposite initially, Vienna and Arizona have very different summer temperatures. In Vienna, summer temperatures range between 26 and 15 degrees. In Arizona, it can reach 40 degrees. All these results allowed us to establish an optimal temperature of 20 degrees.

Comparing studies from two different cities and varying daylight hours also made it possible to remove these parameters from the causes of yawning. Also, it was concluded that yawning decreases at shallow temperatures since refrigeration is not necessary. Therefore, these studies reinforced the previous ones and the theory of refrigeration. Starting today, look at the duration of your yawns. It could mean that you are more intelligent than average and wasting it. Now, jokes aside, stay yawn longer, brain bigger, and above all, more neurons.


  1. Other theories

In this last section, we show a diversity of theories appearing over time, although most do not present any scientific evidence or have even been discarded due to lack of results. For example, another of the most credible explanations would be that yawning is a mechanism to relieve stress and anxiety. It is true that many times when yawning, we feel a sense of peace and well-being similar to that of stretching. However, no conclusive studies establish a direct correlation between yawning and stress relief.

Other research suggests that yawning was an early communication system between primates and humans before speech appeared. Although some studies show that bonobos and humans share some forms of communication and structures, they are far from proving that yawning was a form of primitive language.

Although we have already said that yawning is a “fixed pattern of action,” some researchers propose that it is a reflex preserved since we are in the womb, although this theory does not explain its function either. Maybe I might not have.

This is suggested by some biologists and students of evolution that yawning is an inheritance of the gills of the first amphibians that left the sea to inhabit the land. This could explain why it is a “fixed pattern of action,” something that does not respond to no stimulus. For this theory, yawning is simply an inheritance and has no function.

Some theories try to establish the relationship between yawning and sexual function, more precisely with erections in men. To speculate, we can name numerous theories that explain the process of yawning, but it seems that today there is a winner. The refrigeration theory has been supported by different studies and presents solid results.

However, it presents only a partial explanation. It may be that yawning has more than one function. For example, we still don’t know why yawns spread. One of the hypotheses would be to make people more attentive and the whole group responds as quickly as possible to an external threat. But researchers agree that we still don’t know why we yawn.