New insights into yawning

A good yawn might do more than you think, say researchers!

Why do we yawn? There are several explanations for this everyday quotidian . 

Yawning is an involuntary reflex triggered by tiredness, boredom, stress, or temperature changes, primarily serving to cool down the brain and increase alertness. It involves deep inhalation to enhance blood flow and improve brain thermoregulation. Yawns are also contagious, often linked to empathy and social bonding.

A simple yawn may feel like the most ordinary of human acts—a reflex triggered by tiredness, boredom, or seeing someone else's mouth stretch wide.

Yawning induces simultaneous outflow of cerebrospinal fluid and venous blood from the skull, a pattern distinct from deep breathing, which causes CSF inflow. This fluid movement may contribute to brain waste clearance and thermoregulation, suggesting a physiological role for yawning beyond social or behavioural triggers. Individual tongue motion during yawning is unique and consistent, resembling a biometric signature.

Now, a new imaging study suggests that yawning may play a subtle but intriguing role in moving fluids in and out of the brain. Although the researchers acknowledge the idea is speculative, they say their work introduces an interesting avenue for understanding the physiological functions of yawning.

Using real-time MRI scans, a research team was able to see what happens inside the head and neck when people yawn, and compare it to the effect of normal and deep breathing.

The results, based on a small-scale group of 22 participants and published in Respiratory Physiology & Neurobiology, showed that yawning triggered a specific maneuver in which cerebrospinal fluid (CSF) and venous blood moved out of the skull together, whereas during deep breathing cerebrospinal fluid flowed into the skull.
Cerebrospinal fluid is a clear liquid that surrounds the brain and spinal cord, filling the space around them like water around a floating object. It is important because it cushions and protects the brain and spinal cord from injury and also helps carry nutrients in and waste products out.

The fact that CSF and venous blood flows away from the skull during yawning, but CSF flows in the opposite direction when deep breathing, was a big surprise to the researchers.

They observed that yawning is a body movement that can influence the flow of fluids around the brain.
There has been speculation that yawning can help clear waste from the brain, but so far there has not been solid proof.

This new research suggests that yawning can play a role in cleaning brain fluid, which would most likely happen close to bedtime.
This finding could be important for further studies into neurodegenerative diseases such as Alzheimer's, Parkinson's and dementia—all of which have been potentially linked to the build-up of waste products in and around the brain that can be a result of impaired CSF flows.

The research team also says the evidence suggests yawning is a way for the body to regulate the temperature in and around the brain.

In humans, the brain tissue can be up to 1°C warmer than the rest of the body, and venous blood leaving the brain is typically about 0.2–0.3°C warmer than the arterial blood entering it.
So when someone yawns, we can now see an increase in the cooler arterial blood flow into the skull, compensating for the coupled outflow of CSF and venous blood, and therefore we can surmise there may be a thermoregulatory process happening there.

We could speculate that perhaps yawning is a way that the brain helps to cool itself down, but again we would need to do more research to state that with certainty, say the researchers.

We do know that a hot brain is not a good thing because there is a risk of cell damage, seizures and cerebral swelling. And there is actually a very narrow band temperature-wise where the brain is steady and balanced, what is known as homeostasis.

That's likely the reason why there are so many mechanisms—such as blood flow and sweating—that help regulate temperatures in the brain.

We don't fully know what the level of contribution yawning may play in that, but this research opens up some interesting avenues for further investigation in that area as well.
The researchers also say they have identified for the first time that people appear to have a unique signature to their individual yawn, which can be identified by the complex way their tongue moves during the action.

Another interesting thing they found is that each person yawns in a unique way—so the tongue motion during the yawn is different between people, but very consistent for each person.
And it's not a simple motion. It's a very complex movement of the tongue during a yawn. It's almost like a fingerprint, so you could possibly identify someone just based on how they yawn.

Adam D. Martinac et al, Biomechanics of contagious yawning: Insights into cranio-cervical fluid dynamics and kinematic consistency, Respiratory Physiology & Neurobiology (2026). DOI: 10.1016/j.resp.2026.104575