It’s most commonly assumed that we yawn when we’re tired, but new research suggests that the familiar breathing episode is linked to thermoregulation, or cooling of the brain.
Previously, some scientists assumed that yawning helped to increase oxygen intake, but other studies have shown that there is no link between yawning and increased blood oxygen levels. Scientists are still unsure as to why we yawn, and have spent considerable time trying to figure it out. Now, researchers have linked yawning not to sleepiness — but rather, to temperature. Researchers from the University of Vienna, the Nova Southeastern University, and SUNY College at Oneonta published the recent study in the journal Physiology & Behavior.
“The underlying mechanism for yawning in humans, both spontaneous and contagious, appears to be involved in brain thermoregulation,” the authors wrote in the abstract. They tested various groups of people both in Vienna and Arizona, reviewing pedestrians who were outdoors in summer and winter months. The authors found that people in Vienna yawned more during the summer than in winter, while Arizona folk yawned more during the winter. They also found that Vienna summers and Arizona winters stayed around 20 degrees Celsius — a certain temperature that appeared to increase contagious yawning. Yawning decreased when the weather made its way up to 37 degrees Celsius in Arizona, or when it got colder in Vienna.
Based on these results, Jorg Massen, lead author of the study, believes that yawning isn’t "necessary" during really hot temperatures or really cold ones, either. So even though some scientists have studied emotional-cognitive variables when it comes to yawning, Massen and his team believe that ultimately it all has to do with temperature, even when you think you're only yawning because they're "contagious" when you see someone else yawn.
Source: Massen, J.J.M., Dusch, K., Eldakar, O.T. & Gallup, A.C. “A thermal window for yawning in humans: Yawning as a Brain Cooling Mechanism.” Physiology & Behavior.