Why do your fingers wrinkle in water?

Stay in the bath long enough and your fingertips turn into little prunes. The obvious explanation is that your skin soaks up water, swells and puckers. It sounds so reasonable that most of us never question it. But there is a clue hiding in old medical records that blows that explanation apart.

The short answer

Finger wrinkling is an active process controlled by your nervous system. Since the mid-1930s, scientists have known that when the nerves to a finger have been cut, that finger does not wrinkle in water. If wrinkling were just passive soaking, nerves would not matter at all.

The real story

So what is going on? One leading idea is that, when your hands are wet for a while, the nervous system narrows the blood vessels beneath the skin of the fingertips. The tissue underneath shrinks slightly, and the skin on top buckles into those familiar ridges. The exact mechanism is still being studied, but the nerve connection is well established.

The bigger mystery is why. Why would the body bother to wrinkle your fingers on purpose? In 2011, the evolutionary neurobiologist Mark Changizi and colleagues at 2AI Labs in Boise, Idaho, published a paper in Brain, Behavior and Evolution suggesting an answer. They proposed that the wrinkles act like the tread on a tyre, channelling water away so the fingertips can grip better in wet conditions. They noted that the wrinkles form drainage-like patterns of channels.

In 2013, a Newcastle University team, Kareklas, Nettle and Smulders, tested the idea. Writing in Biology Letters, they reported that volunteers with wrinkled fingers moved wet, submerged objects more quickly than those with smooth fingers, while wrinkles made no difference with dry objects. Case closed? Not quite.

In January 2014, researchers at the Max Delbrück Center in Berlin published a study in PLOS ONE with 40 volunteers and found that wrinkled fingers gave no advantage in gripping wet or dry objects, and made no difference to touch sensitivity. So the twist is twofold: wrinkles are not just soggy skin, and science has not yet settled whether they give us a better grip. The jury, quite literally, is still in the bath.

Why people get it wrong

The soaking explanation fits everyday experience. Wet things swell, paper puckers, sponges expand. Fingers go wrinkly in water, so it must be the same thing. But the decisive evidence comes from people whose finger nerves were damaged: no nerves, no wrinkles. That one observation turns a simple physics story into a puzzle about biology and evolution, and it is a reminder that the most obvious explanation is not always the right one.

The Sole sums it up: “Your fingers don’t go wrinkly by accident. Your brain does it on purpose. We’re just not sure why yet, which is about par for the brain.”