We yawn for several reasons, with no single definitive explanation, but the most supported theories suggest yawning helps cool the brain and regulate its temperature. This cooling effect happens because yawning opens the jaw and increases blood flow to the brain, while the deep inhaling brings cooler air to the blood vessels in the brain. Yawning may also serve as a way to increase alertness, stretch muscles, and prepare the body for a change in activity, such as waking up or becoming more attentive. Additionally, yawning is believed to have social and empathetic functions, as it is often contagious and may communicate feelings like tiredness or boredom and help synchronize alertness within groups.

Brain Cooling Theory

Yawning is thought to cool the brain when it heats up, by opening the skull muscles and increasing blood flow which brings cooler blood to the brain. The deep breath inhaled during a yawn also pulls cooler air into the lungs and blood vessels near the brain, helping regulate brain temperature and maintain optimal functioning.

Alertness and Physiological Effects

Yawning commonly occurs during tiredness, boredom, or transitions between wakefulness and sleepiness. It can help increase alertness by stretching the lungs and muscles and boosting blood flow to the brain, which may explain the quick rise in heart rate that accompanies yawning.

Social and Empathetic Functions

Yawning may have evolved as a communication signal that indicates tiredness or boredom and might support social bonding by synchronizing group alertness. Contagious yawning is linked to empathy, where seeing others yawn triggers a yawn in oneself, especially among close relations.

Other Aspects

• Yawning starts early in the womb and continues through life.
• It can be triggered by factors like changes in elevation (to equalize ear pressure).
• Excessive yawning can sometimes be a sign of medical conditions affecting the nervous or cardiovascular systems.

In summary, yawning helps keep the brain at an optimal temperature, supports transitions in alertness, and may function as a form of social communication linked to empathy and group cohesion.