Why do fingers go wrinkly after a long soak?

On Sunday, Na went swimming with Dad and stayed in the pool for nearly an hour. When she climbed out, all ten fingertips, and her toes too, were wrinkled into ridges. Oddly, her arms and tummy were as smooth as ever.

Cú Bông guessed her skin had soaked up water and swollen, like a sponge in a bucket.

On the way home, Dad talked about Mr Tư next door. Years ago he hurt his wrist, and the nerve to one of his fingers was damaged. Since then, however long he soaks his hands, that one finger never wrinkles. If skin just soaked up water, why would that finger be different?

People used to think wrinkles came only from skin soaking up water, but studies show it isn't that simple. After a long soak, the nervous system makes tiny blood vessels under the fingertip skin narrow. That is what makes the wrinkles.

Because nerves control it, a finger with a damaged nerve may not wrinkle in water. What the wrinkles are for, scientists are still finding out. In one small study, people moved wet objects faster with wrinkled fingers; another study found no difference.

Step through to see how a fingertip wrinkles. At which step does the body start making the finger wrinkle?

Fingers wrinkle after a long soak because the nervous system makes blood vessels under the skin narrow. What the wrinkles are for, scientists are still finding out.