Why do we yawn?

While the exact cause of yawning remains debated, the thermoregulation hypothesis holds the most scientific support. Yawning stretches the jaw muscles, increases heart rate by up to 25%, and draws cool air into the sinuses, collectively cooling the brain. Studies show yawning frequency increases in warmer ambient temperatures and decreases in cold environments. Contagious yawning — triggered by seeing, hearing, or even reading about yawning — is linked to empathy circuits in the brain and appears in humans, chimpanzees, and even dogs. Children under 4 and people with certain empathy-related conditions are less susceptible to contagious yawning.