Why Do We Prune in Water?

Some of our body’s automatic functions remain a mystery. For example, why do our fingers prune after some time in the water? We don’t know, but a new study suggests it improves our grip on wet objects. There’s a term for pruning called water-induced finger wrinkling. Yep, there’s a term for that. 

Here’s how it works. The main nerve running down the arm into the hand called the median nerve controls movement and sensation. It also regulates things we don’t think about, such as sweating and blood vessel constriction.  Researchers believe when our hands are soaked in water, the sweat glands open to let water in, leading to an imbalance in the salts in our skin. This triggers the nerve fibers in the fingers to constrict blood vessels around the sweat ducts. The lack of blood means less volume in the skin, which pulls down the flesh, forming wrinkles.  

To study whether we gain an advantage from this wrinkling, scientists measured the force five hundred people used to grip a plastic object with dry, wet or wrinkled fingers.  As expected, dry hands used less force than wet ones. But when fingers were allowed to wrinkle, the force for wet hands to grip an object dropped by half. So, wrinkling increases friction between wet skin and the object, requiring less energy to hold it, and also the wrinkles allow water to move out more quickly.  

It’s possible our ancestors walked better on wet rocks with wrinkled feet, or their wrinkled hands were better at catching shellfish. We don’t know, but half the fun in research is asking why. Our wrinkled fingers are helping us in ways we’ve yet to discover!