Why Do Your Fingers Wrinkle in Water?

If you love spending time soaking in the tub or swimming in the pool, you probably know that it doesn’t take very long for your fingers to transform, changing from smooth and soft to wrinkly and pruned. But why doesn’t the skin on the rest of your body wrinkle the same way? And what exactly is going on?

This is something scientists have been studying for decades. Initially, many assumed that water around you passes through the upper layers of skin, through a process known as osmosis, causing cells to swell as they get waterlogged. But modern research shows the reason your fingers prune is much more complex. And it involves your nervous system.

Shrinking in the Wash

The outer layer of your skin, called the epidermis, does absorb some water — that much is true. It usually takes between a few minutes and a half hour depending on the water’s temperature. But pruning is way more involved and is controlled by your nervous system, the same network in charge of your fight-or-flight response.

Research published in the British Medical Journal in 1973 confirmed this connection, discovering that injury to the median nerve, which helps you feel and move your fingers, prevented wrinkles from forming on fingers that were submerged in water. The median nerve is part of your sympathetic nervous system, which controls automatic bodily functions such as sweating and blood pressure. 

While scientists still aren’t exactly sure why, the leading theory is that the wrinkling in your fingers happens when nerves trigger blood vessels just below your skin to narrow around sweat glands. This shrinking “pulls” your outer layer of skin inward, making your fingers look like shriveled raisins. The mechanism is called vasoconstriction and it’s controlled by your median nerve.

Vasoconstriction may be the “how” when it comes to your fingers pruning, but it doesn’t explain the “why.”

Early Humans Needed to Get a Grip

There’s evidence that finger pruning has to do with adaptation and evolution, and our fight-or-flight instinct. In fact, several studies have shown that wrinkled or pruned fingers are better at grasping and holding wet objects than smooth and dry fingers. Like textured gloves or treads on a tire, the uneven surface of pruny fingers improves grip by concentrating friction, shifting load, and better interlocking with surface irregularities.

The grooves in waterlogged fingers also channel water away, allowing for better surface contact with what your hands are grabbing. Early humans may have evolved so that our fingers (and toes) prune just enough to help us grip slippery rocks and other slick surfaces when we’re in the water. 

The process is totally normal, and it doesn’t last. Once your skin dries, your blood vessels go back to normal and the wrinkles disappear. (While having better grip 24/7 may seem like a good idea, evolutionarily speaking, it would come at the expense of touch sensitivity.) 

So, the next time you’re lounging in the pool and your fingers look pruned, just know your nervous system is working exactly like it should. It’s even making it easier for you to pull yourself out of the water or grab a nearby drink without spilling it.