After recording the yawning frequency of 160 people in Tuscon, Ariz., during the winter and summer, Gallup’s team found that participants yawned more during the colder season than in warmer weather, when the heat outdoors was higher than 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 countercurrent heat exchange with the ambient air that accompanies the deep inhalation,” Gallup said in a statement.
The mechanism is determined by the surrounding air temperature, according to Gallup. In higher temperatures, the deep inhalation of air involved in a yawn does not encourage cooling.
Gallup noted that his study, published in this month’s issue of Frontiers in Evolutionary Neuroscience, is the first to report seasonal variation in yawning frequency and has broad implications for better understanding diseases and conditions accompanied by frequent yawning.