Why We Yawn, Why Is Yawning Contagious?

The most common answer to this question is that yawning increases the oxygen level in the blood with the oxygen-rich air inhaled, thus helping to eliminate drowsiness. But there is no evidence that yawning affects blood and brain oxygen levels.

Recent studies have shown that yawning has a temperature-regulating effect on the brain. According to this view, deep breathing with a yawn—like the radiator in a car—cools the brain. When the temperature of the brain increases, the blood flow in the nasal mucosa accelerates. Yawning air changes the temperature of the blood in the veins as it passes through the nasal and oral cavities, the walls of which are covered with networks of blood vessels directly connected to the forebrain. Thus, it helps to cool the brain. In the research conducted on mice, it was determined that the temperature of the brain increased before yawning, and then the temperature decreased. However, it was understood that the temperature stabilizing effect of stretching is more pronounced at average temperatures (about 20°C) where the ambient temperature is not too hot or too cold.

So why do we usually yawn before going to sleep, after waking up, or when we’re bored? The brain, which weighs 2% of the body weight, is responsible for 20% of the total energy consumption. Sleep and stress are thought to cause changes in brain temperature. For example, it is known that insomnia increases the temperature of the brain. The reason why yawning is associated with sleep and fatigue may be its effects on brain temperature.

Yawning is also contagious. Watching someone else yawn or reading about yawning can trigger yawning. The contagiousness of yawning is thought to be associated with a sense of empathy. Brain imaging studies have shown that during contagious yawning, the region of the brain that evaluates people’s own and other people’s emotions is active. There are also studies that show that the contagiousness of yawning has no apparent connection with empathy. However, the fact that contagious yawning is less common in individuals with autism and schizophrenia who have impaired social communication skills supports the view that the contagious yawning is related to empathy.

Why does yawning trigger others to yawn?

One is that people yawn when other people yawn due to a phenomenon called echopraxia, in which a person sees a certain behavior and, if they’re sensitive to it, will mimic it. This is made possible by mirror neurons in the brain.