Why Do Fingers Get Wrinkly in the Bath?

The short answer

Wrinkly fingers aren’t just soggy skin. After a few minutes in water, your nerves signal the tiny blood vessels in your fingertips to shrink. The fingertip gets a little smaller underneath, but the skin on top stays the same size, so it folds into wrinkles. Those wrinkles work like the treads on a tire, channeling water away so you can grip wet things better.

It’s your nerves, not just water

For a long time people thought fingers wrinkled simply because the outer skin soaked up water and swelled. But doctors noticed something surprising: if the nerve to a finger has been badly damaged, that finger doesn’t wrinkle in water. So the wrinkling is something your body does on purpose, controlled by nerves.

Here’s what happens. Water soaking into the skin is a signal. Your nervous system responds by squeezing the tiny blood vessels in your fingertips, so they hold less blood. The soft pad under the skin shrinks a little. The skin on top doesn’t shrink, so it buckles into wrinkles, just as a blanket wrinkles if you push its ends together.

Only the skin on your fingers, palms, toes, and soles wrinkles this way, the hairless skin you use for gripping.

Treads for wet grip

Why would your body bother? Scientists tested it ¹. They asked people to move marbles and fishing weights from one container to another using a thumb and finger. Some people had wrinkly fingers from soaking in warm water; some didn’t. With wet objects, the people with wrinkly fingers were faster. With dry objects, wrinkles made no difference.

The idea is the same as car tires. Tires have grooves so that on a wet road, water squirts out through the grooves and the rubber touches the road. Wrinkly fingertips do the same: water flows away through the grooves and your skin touches the object.

Why it comes and goes

Wrinkles take about five minutes or more to appear, and they fade soon after you dry off. Smooth fingertips are better for feeling small details and handling dry things, so it makes sense that the wrinkles only show up when you’ve been in water for a while. Long ago, that might have helped our ancestors grip wet rocks and branches, or catch slippery food in streams.

So

Your fingers wrinkle in the bath because your nerves shrink the blood vessels in your fingertips, making the skin fold into grooves, and those grooves act like tire treads that help you grip things when your hands are wet.