Why do fingers wrinkle when they get wet?

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Some thoughts to reflect on next time you’re in the shower.

Contrary to popular belief, the wrinkle-effect on our fingers may not be caused by water absorption. Instead, pruney fingers may be a valuable adaptation that allows us to grip objects when it is wet. Mark Changizi, an evolutionary neurobiologist at 2AI Labs in Idaho, US, compares our fingertips to the tires of a car, and suggests that the wrinkles may act like rain treads, creating channels that allow water to drain away when our fingers are pressed against a wet surface.

Nearly a century ago, surgeons observed that wrinkling doesn’t occur if a nerve to the finger has been cut. This implies that the formation of water wrinkles is controlled by the nervous system, rather than being an accidental side effect of wetness.

“I stumbled upon these nearly century-old papers and they immediately suggested to me that pruney fingers are functional,” said Changizi on his website. “I discussed the mystery with my student Romann Weber, who said, ‘Could they be rain treads?’ ‘Brilliant!’ was my reply.”

Changizi and his team studied photos of 28 wrinkled fingers. They observed that all of them had the same pattern — long, unconnected channels branching from a point at the top of the finger. Changizi explains that when we press down with a finger, we apply pressure from the tip backwards. The flat part of our fingers acts like a plateau where water can pool, which is why wrinkles form here — to channel the water away.

Changizi now wants to see if mammals that live in wet habitats are more likely to develop wrinkled fingers. After observing photos of bathing Japanese macaques, he found a photograph of one of the macaques with wrinkly fingers; leading him to believe that it’s most likely other bathing animals will have the same result.

The ultimate test will be to see if people with wrinkled fingers are better at gripping in wet conditions. Although the experiments are only in their pilot phase, Changizi says that the results are promising to support his theory.

Source: 2AI Labs