Why do we yawn when we see someone else doing it?

How many times has it happened to you that you see someone yawn and you can’t stop yourself from doing the same. Or you’re in an important meeting and bam! your mouth opens accidentally. And the most disturbing thing is that many times you don’t even feel particularly tired or bored. However, you cannot avoid that gesture in bad taste when done in public, which also tends to stalk us at the least appropriate moment. “Yawning is a stereotyped movement that consists of a deep inhalation with the mouth open, a climax phase in which there is maximum stretching of the muscles of the neck and pharynx and a short exhalation,” clarifies Noelia Valle, professor of Physiology from the Francisco de Vitoria University, before explaining why our body reacts this way.

The act of yawning, which we carry out since we are fetuses, is not exclusive to humans. Mammals do it, but also amphibians, birds, reptiles and even fish. And the moment when our mouths open the most is “the interval between sleep and wakefulness, when hungry and in stressful situations, as happens to some athletes just before a sports competition,” adds the expert.

The myth of oxygenation

So why do we yawn? «Let’s start by dismantling a myth – says Noelia Valle –. We don’t do it to get more oxygen to the brain. This theory was refuted more than 30 years ago when it was shown that breathing high levels of oxygen or carbon dioxide or performing physical exercise did not influence yawning. Furthermore, the oxygenation hypothesis would not explain why the fetus does it. It is true that the maximum stretching of the neck and pharynx muscles that occurs during yawning would help tone these muscles. This seems to make them more efficient at opening the airways, providing a greater amount of oxygen. However, this increase would be a long-term result, not an immediate effect.

Having discarded the theory of brain oxygenation as the main hypothesis of why we yawn, scientists have come to the conclusion that we take this deep breath to keep our head cool. “Like computers, the human brain is very sensitive to temperatures and must remain cool to operate efficiently,” explained the authors of an ambitious study on the causes of yawning, led by the American universities of Maryland and Princeton.

At night and when you wake up

After observing a total of 1,291 yawns from 101 different species of mammals and birds, it was also observed that the greater the size of the brain and the number of neurons, the number of deep inspirations increased. “In other words, larger brains need to yawn more because, by generating more heat, they require more cooling,” experts agree.

At what time of day does our mouth open the most? «Humans yawn more at night – a time when brain temperature is at its maximum – and when we wake up, a time when our head thermometer begins to rise from its lowest point. Yawning contributes to reducing brain temperature, which helps us maintain concentration and attention in order to counteract sleepiness,” argues Noelia Valle.

However, despite what we might think, we open our mouths more in winter than in summer. An experiment conducted in Tucson, Arizona, showed that the number of contagious yawns decreased with heat. When the temperature increased, the study participants yawned more to cool their brains, but this only happened at the beginning of the test, since, after a few minutes, the opposite happened. They inhaled less to avoid precisely the opposite effect. “In conclusion, all this makes us predict that boredom warms up our brain,” warns the expert.