For many, shaking one’s head to drain out any water that may have become trapped after that epic cannonball or graceful swan dive is a summertime rite of passage. But new research suggests that the tell-tale nodding can cause brain damage in small children.
A collaborative study conducted by researchers at Cornell University and Virginia Tech found that the damage depends on just how hard a child jerks their head. The findings were presented at the American Physical Society's Division of Fluid Dynamics 72nd Annual Meeting in Seattle over the weekend.
In their abstract, the study authors write that they used glass tubes of varying diameters that were closed on one end to represent the ear canal. They then dropped the tubes onto a spring to mimic how a child might shake their head. This dropping mechanism creates deceleration, which study author Sungwan Jung told IFLScience is "similar to when the head is shaken side to side."
"Our research mainly focuses on the acceleration required to get the water out of the ear lobe. The critical acceleration that we obtained experimentally on glass tubes and 3D printed ear canals was around the range of 10 times the force of gravity for infant ear sizes, which could cause damage to the brain,” said researcher Anuj Baskota in a statement.
This “critical acceleration,” they note, tends to be higher in smaller tubes, suggesting that shaking one's head to drain any trapped water may be “more laborious to children due to their small size of the ear canal” compared to adults.
"From our experiments and theoretical model, we figured out that surface tension of the fluid is one of the crucial factors promoting the water to get stuck in ear canals," said Baskota.
Adults and children alike will often shake their head after coming into contact with water to avoid swimmer’s ear (Otitis externa), an infection in the outer ear canal that results from bacteria growing in the now-moist environment, according to the Mayo Clinic. Swimmer’s ear is characterized by itching in the ear canal and discomfort that worsens over time. It can be particularly painful in young children.
But shaking one’s head isn’t the only solution to drain trapped water and prevent a potential infection.
"Presumably, putting a few drops of a liquid with lower surface tension than water, like alcohol or vinegar, in the ear would reduce the surface tension force allowing the water to flow out," said Baskota.