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Sometimes it takes a kid to ask a question no one has considered before.

A couple of years ago, ������ý Associate Professor Guy German published research about why human skin wrinkles when you stay in the water too long. Received wisdom held that the water swelled your skin and made your fingers wrinkly, but little to no research had been done to prove that.

What German and his team at the Biological Soft Matter Mechanics Laboratory found is that blood vessels beneath the skin actually contract after prolonged immersion, and that’s where the wrinkles come from.

— a nonprofit news organization that asks academics to share their expertise on current topics — as part of its Curious Kids feature. One of the follow-up questions stumped him, though.

“A student asked, ‘Yeah, but do the wrinkles always form in the same way?’ And I thought: I haven’t the foggiest clue!” said German, a faculty member at the Thomas J. Watson College of Engineering and Applied Science’s Department of Biomedical Engineering. “So it led to this research to find out.”

In , German and Rachel Laytin ’23, MS ’24, show that, yes, the topography patterns remain constant after multiple immersions.

“Blood vessels don’t change their position much — they move around a bit, but in relation to other blood vessels, they’re pretty static,” German said. “That means the wrinkles should form in the same manner, and we proved that they do.”

The research put subjects’ fingers in water for 30 minutes, taking photos and then repeating the immersion under the same conditions at least 24 hours later. By comparing the images, German and Laytin found the same patterns of raised loops and ridges after both immersions.

They also made an interesting side discovery: “We’ve heard that wrinkles don’t form in people who have median nerve damage in their fingers,” German said. “One of my students told us, ‘I’ve got median nerve damage in my fingers.’ So we tested him — no wrinkles!”

As much fun as it was to figure out something a child asked, the research also could have real-world applications in forensics, such as fingerprinting at crime scenes and identifying bodies found after prolonged water exposure. German’s father, a retired U.K. police officer, faced some of these challenges during his law enforcement career.

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

German is eager to further explore questions about skin immersion with his students: “I feel like a kid in a candy store, because there’s so much science here that I don’t know. We thank the people at The Conversation and the wonderful question they asked us, because it does create cool new science.”