A common belief is that yawning helps to increase the oxygen supply. However, previous research has failed to show an association between it and blood oxygen levels. New research by a team led by psychologist Andrew Gallup of SUNY College at Oneonta now reveals that yawning cools the brain.

To test this, Jorg Massen and Kim Dusch of the University of Vienna measured frequencies of pedestrians outdoors in Vienna, during both the winter and summer months, and then compared these results to an identical study conducted earlier in the arid climate of Arizona. Pedestrians were asked to view a series of images of people yawning, and then they self-reported on their own behavior.

Results showed that in Vienna people yawned more in summer than in winter, whereas in Arizona people yawned more in winter than in summer. It turned out that it was not the seasons themselves, nor the amount of daylight hours experienced, but that contagious yawning was constrained to an optimal thermal zone or range of ambient temperatures around 20 degrees C.

In contrast, it diminished when temperatures were relatively high at around 37 degrees C in the summer of Arizona or low and around freezing in the winter of Vienna. Lead author Massen explains that it is not functional when ambient temperatures are as hot as the body, and may not be necessary or may even have harmful consequences when it is freezing outside.