Jorg Massen and Kim Dusch conducted the study, which tried to find the range of temperatures that causes yawning frequency to increase or decrease. They conducted identical studies on pedestrians yawning patterns in Vienna, Austria and Arizona in the winter and summer months.
They concluded that people are most likely to yawn at 68 degrees. When it is warmer outside, people are less likely to yawn, because it has little effect on the brain's temperature. In freezing temps, yawning may be unnecessary or even harmful.
Factors like lack of sleep and stress can also contribute to the brain overheating, causing a person to yawn more frequently. Scientists are still searching for the cause of contagious yawning, which happens when a person sees someone yawn and feels the need to yawn, too.
The researchers said they have a strong hypothesis, but it's not definite. Since yawning cools the brain and improves mental efficiency, they think that contagious yawning could be an effort to enhance group vigilance.