It is now cool to yawn as has been indicated in a study by Princeton University's Department of Ecology and Evolutionary Biology.

In a landmark discovery, yawning has literally been linked to hot-headedness. The study explains that while yawning frequencies are seasonal, people are less likely to yawn when the heat outdoors exceeds body temperature.

Thus, yawning is a characteristic that is not evoked due to boredom, sleep or fatigue alone. In fact, the study supports the thermoregulatory hypothesis stating that yawning is triggered by increases in brain temperature, and that the physiological consequences of a yawn acts to promote brain cooling.

This report is a first of its kind that shows that yawning frequency varies from season to season. When applied to real-life, the study data is likely to benefit a better understanding of diseases and conditions, such as multiple sclerosis or epilepsy which are frequently accompanied by yawning and thermoregulatory dysfunction.

These results provide additional support to utilize occurrences of yawning as a diagnostic tool for identifying instances of diminished thermoregulation.

Lead author, Andrew Gallup of Princeton University and co-author Omar Eldakar, a post-doctoral fellow in the University of Arizona's Centre for Insect Science noted that yawning could serve as a method for regulating brain temperature.

Published in the journal Frontiers in Evolutionary Neuroscience, the authors concluded that according to the thermoregulatory theory of yawning, warmer temperatures might not provide instant relief for overheated brain, which stays cooler due to the heat exchange occurring when the air is drawn in during a yawn!

Likewise, the researchers inferred that participants were more likely to yawn in the winter, as opposed to the summer when ambient temperatures were equal to or exceeding body temperature.

The cooling effect of yawning is thought to result from enhanced blood flow to the brain caused by stretching of the jaw, as well as counter current heat exchange with the ambient air that accompanies the deep inhalation, noted Gallup .

Gallup and Eldakar conducted field studies to explore the relationship between ambient temperature and yawning frequency. They measured the incidence of yawning among people outdoors during the summer and winter months in Arizona. Summer conditions provided temperatures that matched or slightly exceeded body temperature (an average of 98.6 degrees Fahrenheit) with relatively low humidity, while winter conditions exhibited milder temperatures (71 degrees Fahrenheit on average) and slightly higher humidity.

They then randomly selected 160 pedestrians (80 for each season) and, because yawning is contagious, had them view images of people yawning.

 Our study accordingly showed a higher incidence of yawning across seasons when ambient temperatures were lower, even after statistically controlling for other features such as humidity, time spent outside and the amount of sleep the night before. Nearly half of the people in the winter session yawned, as opposed to less than a quarter of summer participants, the study authors said.

The authors also noted that yawning was related to the length of time a person spent outside exposed to the climate conditions. This was particularly true during the summer when the proportion of individuals yawning dropped significantly as the length of time spent outside increased prior to testing.

Nearly 40 percent of participants yawned within the first five minutes outside, but the percentage of summertime yawners dropped to less than 10 percent thereafter. An inverse effect was observed in the winter, but the proportion of people who yawned increased only slightly for those who spent more than five minutes outdoors.

So, do not forget to yawn next time you are outdoors!