The most common medical problems that are associated with increased yawning are sleep deprivation, insomnia, sleep apnea, narcolepsy, and many medicines that cause sleepiness.

Another theory is that yawning stretches the lungs and lung tissue. Stretching and yawning may be a way to flex muscles and joints, increase heart rate, and feel more awake.

Researchers initially thought that yawning might mean you lack oxygen, but more recent evidence suggests this is untrue.

Yawning may aid in brain thermoregulation, or the process by which the brain maintains its core temperature. During a yawn, the facial muscles move and contract, increasing blood flow to the face where heat can dissipate more easily. Some people's eyes tear up when they yawn, which may also release heat.