A Familiar Phenomenon, Unraveled
After a long swim or a relaxing soak in the pool, your fingertips and toes often emerge wrinkled and pruney. But have you ever noticed that these wrinkles form in the same pattern every time? A new study published in the May 2025 issue of the Journal of the Mechanical Behavior of Biomedical Materials reveals why: the folds follow the paths of blood vessels beneath the skin, which remain consistent across repeated exposures to water.
Debunking the Swelling Myth
For years, many assumed that wet skin wrinkles because it absorbs water and swells. However, research from two decades ago overturned this idea, showing that the puckering results from blood vessel constriction. When water seeps into the skin, it dilutes the salt concentration in the tissue. Nerves detect this change and signal the brain, which responds by instructing blood vessels in the fingers and toes to narrow. This pulls the anchored skin inward, creating the characteristic ridges. This evolutionary adaptation enhances grip in wet conditions, much like tread on a tire.
A Curious Question Sparks Discovery
The study began with a simple question posed to Guy German, a biomedical engineer at Binghamton University, New York, during his work with The Conversation. A reader asked, “Do wrinkles form the same way every time?” Intrigued and unsure of the answer, German and his graduate student, Rachel Laytin, designed an experiment to find out.
They recruited three volunteers to submerge their right hands in 40°C water for 30 minutes. After each soak, the team photographed the participants’ pruney fingertips. The process was repeated at least 24 hours later. By overlaying images of the same finger from different days, they found that the wrinkle patterns were nearly identical, with corresponding folds matching in location and shape. Mathematical analysis confirmed the consistency of these patterns.
Wrinkle patterns on a finger pad after two water soaks, with consistent wrinkles in black and inconsistent ones in red (Image Credit: R. Laytin and G. K. German/Journal of the Mechanical Behavior of Biomedical Materials, 2025)
What Drives the Consistency?
The study suggests that the fixed arrangement of blood vessels beneath the skin dictates the wrinkle patterns. Since these vessels remain stable over time, the skin folds along the same paths with each soak. This discovery raises new questions: Do these patterns remain consistent over years or even decades, like fingerprints? If so, could pruney finger patterns serve as a biometric identifier in forensic science?
“I’m fascinated by how a simple question opened up a new avenue of research,” German says. “We’re now curious whether these patterns hold steady over a lifetime, which could have exciting applications.”
Looking Ahead
German’s team plans to investigate whether blood vessel arrangements in fingers remain constant over long periods, such as years or decades. If they do, this could lead to novel uses in biometric identification or forensic analysis. The research also highlights the power of curiosity-driven science, sparked by a reader’s innocent question.
