While we no longer dismiss yawning as “vulgar”, it is seen as rude and disrespectful because it implies that the yawner is bored and is making no attempt to conceal the fact. Of course, this is not necessarily the case and sometimes overwhelming fatigue can cause a bout of yawning.

Yawning is also pandiculation. The process happens in three stages: contraction, release and then lengthening of the muscles to their natural resting length. It is the release of tension, the sensation of the muscles softening, that feels so good.

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.

It can be for many reasons having to do with your body either needing more oxygen or using it to regulate your internal temperate or pressure in the ears. It also promotes wakefulness and attention, which is why we associate it with being tired or not getting enough sleep.