Why Do Fingers Wrinkle After Soaking in Water?

When fingers wrinkle after being immersed in water, the traditional explanation is that the outer skin simply absorbs water and swells. That does not explain why the effect is concentrated on the palm-side surfaces of fingers and toes, or why nerve damage can prevent normal wrinkling in the affected area. Current evidence indicates that water entering around sweat ducts alters the local environment and triggers sympathetic nerve activity. Small blood vessels in the fingertip constrict, slightly reducing the volume of the finger pad, and the overlying skin forms ridges and valleys.

This is not uniform swelling like a sponge. It is an active response involving nerves, blood vessels and the mechanical properties of skin. A 2013 experiment found that wrinkled fingers handled submerged objects more quickly, encouraging the idea that the grooves help drain water rather like tyre tread. Later studies have not found the same advantage in every task, so improved wet grip is a supported but unsettled functional explanation.

The firmer conclusion concerns mechanism: water-induced wrinkling depends largely on nerve-controlled vasoconstriction. Why evolution retained the response cannot be settled by an appealing analogy alone.

https://pubmed.ncbi.nlm.nih.gov/15095056/
https://pmc.ncbi.nlm.nih.gov/articles/PMC3639753/