Why do our fingers wrinkle in water?

For a long time, pruney fingers were thought to be caused by water soaking into the outer skin layer. However, researchers discovered that fingers with severed nerves do not wrinkle, proving it is an active response controlled by the sympathetic nervous system. The nerves constrict small blood vessels in the fingertips, reducing blood volume and causing the skin to fold into grooves. One hypothesis is that wrinkled fingers improve grip on wet objects, much like tyre treads channel water. A 2013 study found that participants with wrinkled fingers could pick up wet marbles faster, though later studies were less conclusive.