A team of international researchers looked at how often people yawned in Vienna, Austria, and Arizona, in the US, during winter and summer.
They found that people in Arizona yawn more in the winter than in the summer; the opposite happened in Vienna, were people yawn more during summer.
The results had nothing to do with the seasons themselves or with other factors, such as stress, boredom or light exposure, these were correlated to an optimal thermal zone (20 to 37 degrees Celsius).
Spontaneous and contagious yawning cools the brains and is not necessary when temperatures are as hot as the body, explained lead researchers Jorg Massen in a news release. He also pointed out that yawning may not be necessary or may even be a bit dangerous when it’s freezing outside.
Every time we yawn our jaw stretches, increasing the blood flow to the brain, and the deep inhalations of fresh air help cool down the brain. Discover more about yawning in this AsapScience video: