As summer swimmers plunge into pools and lakes, they often notice a familiar transformation — fingers turning wrinkly after a long soak. But what many may not realize is that these "pruney" patterns form in exactly the same way every time — and that could have important forensic implications, according to new research from Binghamton University, State University of New York.

In a study published in the Journal of the Mechanical Behavior of Biomedical Materials, researchers from the university’s Biological Soft Matter Mechanics Laboratory confirmed that water-induced finger wrinkles are not random. Rather, they are driven by the contraction of blood vessels beneath the skin — not by water absorption, as commonly believed — and they appear in consistent patterns each time a person’s fingers are submerged.

“Blood vessels don’t change their position much — they move around a bit, but in relation to other blood vessels, they’re pretty static,” explained Dr. Guy German, associate professor of biomedical engineering at Binghamton’s Thomas J. Watson College of Engineering and Applied Science. “That means the wrinkles should form in the same manner, and we proved that they do.”

The research was sparked by a curious question from one of German’s students: “Do the wrinkles always form in the same way?” That simple query led to a follow-up investigation by German and graduate student Rachel Laytin. Participants soaked their fingers in water for 30 minutes, had their wrinkles photographed, and then repeated the process after 24 hours. The same raised loops and ridges appeared each time, confirming the hypothesis.

But the study didn’t stop there. The team also discovered that people with median nerve damage — the same nerve affected in carpal tunnel syndrome — do not develop these water wrinkles.

“One of my students mentioned having median nerve damage in his fingers, so we tested him — and no wrinkles formed,” German said.

This insight could have real-world forensic applications. In cases involving drowning or prolonged water exposure, predictable wrinkle patterns could assist in identifying bodies or refining fingerprint techniques. With a father who served as a police officer, German has long been fascinated by forensic science and biometrics.

“Biometrics and fingerprints are built into my brain,” he said. “I always think about this sort of stuff, because it’s fascinating.”

The research opens new doors for understanding how the skin interacts with water and how subtle biological cues might one day assist in criminal investigations or medical diagnoses. German and his team say they’re just getting started.

“I feel like a kid in a candy store,” he said. “There’s so much science here that I don’t know — and that’s exciting.”