We’ve all experienced that urge to open our mouths wide, take a deep breath, and stretch our facial muscles. But why do we yawn, and what explains the phenomenon of contagious yawning?
Scientifically, yawning is the synchronized motion of the thoracic muscles in the chest, the diaphragm, the larynx in the throat, and the palate in the mouth. This act helps to distribute surfactant, a wetting agent, to cover the alveoli, which are tiny air sacs in the lungs [3]. The brain, particularly the hypothalamus, plays a central role in triggering and regulating yawning. This seemingly simple action, however, sets off a cascade of changes within the body. Yawning increases heart rate, facilitates blood flow, and enhances oxygen intake.
The precise reason for why we yawn is still researched and debated by doctors and scientists. However, the most common explanations revolve around yawning being used as a way to keep us as alert. Yawning is considered a brain cooling mechanism which leads to an increase in peripheral and cerebral blood flow. The rhythmic contraction and relaxation of facial muscles during a yawn enhance blood flow in the face, leading to the dissipation of heat through emissary veins connecting the surface of the head with the internal blood vessels. Furthermore, the act of gaping the mouth and inhaling cool air during a yawn influences the temperature of the blood traveling from the lungs to the brain through convection [2].
Another explanation is drowsiness being a common stimulant for yawning, with boredom leading to drowsiness as the primary source of stimulation diminishes. Studies demonstrate a significant increase in physiological arousal after yawning, shown in increased heart rate and skin conductance levels. This arousal response is likened to the effects observed with caffeine intake, supporting the idea that yawning plays a role in the brain’s arousal reflex. Additionally, the frequency of yawning is noted to be associated with viewing uninteresting stimuli and activities requiring minimal interaction, reinforcing the idea that yawning subserves arousal and higher brain activation [2].
What is known is that yawning is undeniably contagious, with a single person’s yawn capable of inducing yawning in an entire group. People with higher empathy levels are believed to be more susceptible to yawning in response to others as brain imaging studies have revealed that observing someone yawn activates brain areas associated with social functions. Interestingly enough, this phenomenon extends beyond humans, as dogs also yawn when witnessing their owners or strangers yawn, and similar contagious yawning has been observed in various animals [4].
Moreover, when members of a group yawn together, it could help align their mental states, making them more synchronized. This synchronization is believed to serve as a form of collective alertness, helping the group become more aware of external threats more rapidly than if each individual were to respond independently. As a result, the spread of yawning in a group is thought to be a way for individuals to share a collective state of readiness and awareness [4].
Recent research has shed light on the influence of breathing methods and forehead temperature on the contagious nature of yawning. A study exploring these factors found that nasal breathing acted as an antagonist to contagious yawning, significantly reducing its incidence. Participants engaging in other breathing conditions, however, yawned approximately 48% of the time. Moreover, applying a cold pack to the forehead greatly diminishing contagious yawning, while warm and room temperature packs showed no such impact. The combined conditions thought to promote brain cooling, involving nasal breathing and forehead cooling, virtually eliminated contagious yawning, since only one out of 22 participants experienced yawning. These findings highlight the connection between physiological factors, particularly breathing patterns and thermoregulation, and the occurrence of contagious yawning [1].
As research on the science of yawning advances, we can continue to discover more about this seemingly simple act. So the next time you feel that familiar yawn coming on, remember that you’re engaging in a fascinating scientific phenomenon!
References:
- Gallup, A. C., & Gallup, G. G. (2007). Yawning as a brain cooling mechanism: Nasal breathing and forehead cooling diminish the incidence of contagious yawning. Evolutionary Psychology, 5(1), 147470490700500. https://doi.org/10.1177/147470490700500109
- Gupta, S., & Mittal, S. (2013). Yawning and its physiological significance. International Journal of Applied and Basic Medical Research, 3(1), 11–15. https://doi.org/10.4103/2229-516x.112230
- Science Reference Section, Library of Congress. (2019, November 19). Why do we yawn?. The Library of Congress. https://www.loc.gov/everyday-mysteries/biology-and-human-anatomy/item/why-do-we-yawn/#:~:text=A%20yawn%20is%20a%20coordinated,we%20cannot%20yawn%20on%20command.
- Rabin, R. C. (2019, February 22). Why do we yawn?. The New York Times. https://www.nytimes.com/2019/02/22/well/live/why-do-we-yawn.html
