A yawn is a reflex. There is the simultaneous inhalation of air and the stretching of the eardrums, followed by an exhalation of breath. Many animal species, including birds and fish, experience yawning. Chasmology is the study of yawning.
Yawning is sometimes viewed as disrespectful. Ibn Hajar, an Islamic theologian, mentions that yawning, in addition to its risks of letting demons enter or take hold of one’s body, is unbefitting for humans as it makes them look and sound like dogs by crooking men’s upright posture and making them howl. An open mouth has been associated with letting good immaterial things (such as the soul) escape or letting bad ones (evil spirits) enter, and yawning may have been thought to increase these risks.
Covering the mouth when yawning may have been a way to prevent such transmission. Exorcists believe yawning can indicate that a demon or possessive spirit is leaving its human host during the course of an exorcism. Thus, covering one’s mouth has been conceived as a protective measure against this.
It is commonly associated with tiredness, stress, sleepiness, boredom, or even hunger. In humans, yawning is often triggered by the perception that others are yawning. This “contagious” yawning has also been observed in chimpanzees, dogs, cats, birds, and reptiles and can occur between members of different species.
During a yawn, muscles around the airway are fully stretched, including chewing and swallowing muscles. Due to these strong repositioning muscle movements, the airway (lungs and throat) dilates to three or four times its original size. The tensor tympani muscle in the middle ear contracts, which creates a rumbling noise perceived as coming from within the head; however, the noise is due to mechanical disturbance of the hearing apparatus and is not generated by the motion of air.
Yawning is sometimes accompanied, in humans and other animals, by an instinctive act of stretching several parts of the body including the arms, neck, shoulders, and back. There are many theories on why we yawn.
Here are a few:
- One theory holds that yawning may help keep the brain awake during boring or passive activities. When one’s blood contains increased amounts of carbon dioxide and therefore becomes in need of the influx of oxygen (or expulsion of carbon dioxide) that a yawn can provide. Yawning may reduce oxygen intake compared to normal respiration, however, the frequency of yawning is not decreased by providing more oxygen or reducing carbon dioxide in the air.
- Yawning, especially psychological “contagious” yawning, may have developed as a way of keeping a group of animals alert. If an animal is drowsy or bored, it will be less alert than when fully awake and less prepared to spring into action. “Contagious” yawning could be an instinctual signal between group members to stay alert.
- Nervousness – evidence suggests that yawning helps increase a person’s alertness. Paratroopers have been noted to yawn during the moments before they exit their aircraft and athletes often yawn just before intense exertions.
- Controlling brain temperature – Mammalian brains operate best within a narrow temperature range. The most scientifically backed theory about why we yawn is brain temperature regulation. A study published in the journal Physiology & Behavior looked at the yawning habits of 120 people and found that yawning occurred less during the winter. If the brain’s temperature gets too far outside of the norm, inhaling air can help cool it down.
- To periodically stretch the muscles of the throat, which may be important for efficient vocalization, swallowing, chewing, and also keeping the airway wide.
- Yawning behavior may be altered as a result of medical issues such as diabetes, stroke, or adrenal conditions. Excessive yawning is seen in immunosuppressed patients such as those with multiple sclerosis. A professor of clinical and forensic neuropsychology at Bournemouth University has demonstrated that cortisol levels rise during yawning.
- In animals, yawning can serve as a warning signal. Charles Darwin’s book, The Expression of the Emotions in Man and Animals, mentions that baboons yawn to threaten their enemies, possibly by displaying large canine teeth. Similarly, Siamese fighting fish yawn only when they see a conspecific (same species) or their own mirror-image, and their yawn often accompanies an aggressive attack. Guinea pigs also yawn in a display of dominance or anger, displaying their impressive incisor teeth. This is often accompanied by teeth chattering, purring, and scent marking.
- Yawning helps open your eustachian tubes, which connect your throat to your ear. This action can help relieve the uncomfortable pressure buildup that occurs when the ear does not have time to equalize, such as when a plane is landing. That said, since swallowing achieves the same purpose, scientists do not believe this is the primary reason we yawn.
If I can yawn when I’m at high altitudes it clears the pressure in my ears temporarily.Doyle
The average person yawns up to 28 times per day, usually after waking up and before going to bed. Yawning in the absence of tiredness, boredom, contagion, or other typical cues is also considered abnormal and may indicate an underlying disorder.
- Ibn Ḥajar (February 18, 1372 – February 2, 1449) was a classical Islamic scholar and polymath “whose life work constitutes the final summation of the science of Hadith.” He authored 150 works on hadith, history, biography, tafsir, poetry, and Shafi’i jurisprudence, the most valued of which is his commentary of Sahih al-Bukhari, titled Fath al-Bari.