Researchers first thought that we yawn to help up our O2 levels, but a new study published in Physiology & Behavior suggests otherwise.

We yawn to cool down our brain, suggest researchers at the University of Austria, Nova Southeastern University and SUNY College at Oneonta. According to these researchers, there ought to be optimal thermal window when yawning is more common. The pattern researchers found was frequency of yawning should increase with rises in ambient temperature – the temperature in a room or the temperature surrounding an object – but as ambient temperature gets close to body temperature, yawning should decrease and decline when ambient temperature falls below a certain point.

If ambient temperatures near body heat, yawning no longer cools the brain. However, yawning in cold temperatures may not be necessary and could even be harmful when outside temperatures are freezing, say the authors.