The Science Behind Hiccups and Yawns



BOTH HICCUPS AND YAWNS can be triggered by the way air enters the body.  Also, both are related to activity of the vagus nerve, which regulates the body’s organs — in particular the heart and blood vessels — and conveys information about them to the central nervous system.

The vagus nerve meanders up the body to affect bodily functions including heart rate, sweating and speech; also the inner portion of the outer ear — creating an ear-throat connection that explains why clearing earwax can cause coughing.  (The vagus nerve comprises more than 80% of the body’s afferent nerves, which affect the subject, as opposed to efferent nerves that allow the subject to effect change.)  Breathing more quickly or slowly can alter vagus nerve activity, which in turn can cause fainting.


Hiccups can erupt when eating too fast causes air to get trapped between pieces of food: the compressed air physically impacts the vagus nerve as it runs up from the diaphragm. Long-term hiccups can be traced to vagus nerve damage or to local irritation, for example, when something in the ear like a hair touches the eardrum.  (The longest attack of hiccups lasted 68 years, estimated at 430 million hiccups, according to Guinness World Records.)

Found only in mammals, hiccups may be an evolutionary remnant of earlier amphibian respiration.  Or because they are more common in infants and become rarer with age, hiccups may have evolved to release air trapped in nursing infants’ stomachs.

Holding the breath or breathing into a paper bag can stop hiccups by raising carbon dioxide levels and inhibiting diaphragmatic activity.  Alternatively, swallowing dry bread or crushed ice can irritate the pharynx, which in turn stimulates the vagus nerve to stop the hiccups.  Folk remedies include drinking a glass of water upside down, gargling, being frightened, eating peanut butter and placing sugar on or under the tongue.

Anecdotal evidence supports applying lidocaine (2-3% is recommended) to the inner ear canal, or squirting vinegar into the nostrils.  Stronger drugs can help with more serious cases.

Birds, fish and snakes, as well as mammals, yawn.  Excessive yawning can be related to the degree that chemicals, such as dopamine and serotonin, are activated in the brain as a result of, for example, intense concentration or creative thinking.  Yawning, which expands the passage from the back of the throat to the eardrums, can also be caused by problems in the heart or blood vessels that stimulate the vagus nerve.

In addition to intense thinking, sleep deprivation, including that due to narcolepsy and hypersomnia, causes brain temperature to rise. Yawns increase blood flow to the brain to move heat away.  Yawns cause the sinuses to act like bellows that cool the brain, according to Gary Hack of the University of Maryland and Andrew Gallup of Princeton University.

With the understanding that yawning is often contagious, the researchers found that subjects who applied cold packs to their heads yawned less often in reaction to others’ yawning, and those who breathed through their noses did not yawn responsively at all —compared to 48% of mouth breathers.

Contagious yawning — also called social yawning — increases around age 4 along with the development of empathy, lessens in old age, and is more common among friends and family members. Men yawn more than women, possibly because women are more “socially aware,” explains psychiatry professor Walter Smitson at the University of Cincinnati.

On the other hand, groups with greater immunity to social yawning include psychopaths and children on the autism spectrum — due both to lack of empathy and to fearlessness, according to Baylor University researchers.  The more coldhearted — on the psychopathy — scale, i.e., the less empathetic — the more immune people were to others’ yawns.   And those who are less fearful — measured as less likely to startle — are less likely to catch yawns.  Physiologically, yawning boosts your blood pressure and heart rate. Paratroopers often yawn just before jumping.

Because yawning is seen as an expression of negative emotions — anger, boredom, disagreement or rejection — and thus ill-mannered, polite yawners cover their mouths with their hands, and people search for ways to catch yawns before the need-to-stifle stage. In anticipation of a potentially yawn-inducing event, the most efficient strategy is to cool the brain: drink or eat something cool, keep the environment cool or apply a cool compress to the head for a minute or two ahead of time.  In the absence of foresight or cooling options, a few deep breaths through the nose, exhaling through the mouth, can help.

Yawns last an average six seconds. The technical name for a yawn is disambigulation; yawning and stretching at the same time is pandiculation, according to Ward Degler in the Zionsville Times Sentinel.  Degler tells about his childhood experiences of trying to hide yawns by pulling his shirt over his face or covering his face with a pillow — about as successful as hiding hiccups.

Although hiccups are unpleasant for the person experiencing them, yawns bother other people more.  Spreading the word about the paratroopers, as well as that yawns indicate serious thinking might someday make them a welcome sign of bravery, intelligence and creativity.

— Mary Carpenter
Mary is the Well-Being editor of MyLittleBird.com. Read more about Mary here.
Her last post was on gadgets that help you relax. 

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