Fingers prune due to an involuntary nervous system reaction that constricts blood vessels beneath the skin. Neurobiologist Mark Changizi of 2AI Labs in Boise, Idaho believes this to be an evolutionary process to increase grip in wet conditions.
The wrinkles on fingertips act as drainage treads, pushing water away and improving traction on other wet objects, states Scientific American. Popular belief that skin pruned due to water being absorbed by outer skin layers has been proven false since the 1930s. In patients with nerve damage to fingertips, pruning does not occur, which would make no difference if it were a matter of absorption.