Why Do Fingers Wrinkle in Water?

When fingers wrinkle after spending time in water, the usual explanation is that the skin has absorbed water and swollen. The outer layer does absorb water, but the familiar ridges on the fingertips are not merely the passive result of softened material. Studies have found that blood flow in the digits falls during immersion. Fingers without normal sympathetic nerve supply may fail to wrinkle in the same way, showing that nerve-triggered vasoconstriction is central to the response.

As the vessels constrict, the tissue volume inside the fingertip decreases while the area of the surface skin does not shrink at the same rate. Grooves form, rather like a thin sheet attached to a smaller layer beneath it. Wrinkling is concentrated on the hairless gripping skin of the palms and soles, which also fits this mechanism better than the idea that all skin simply reacts alike to water.

Why does the body do this? One appealing explanation is that wrinkles work like drainage channels in a tyre and improve wet grip. The experimental evidence is mixed. One study found that wrinkled fingers reduced the force needed to hold wet objects, while another found no improvement in dexterity or touch. The evidence is therefore strong that vasoconstriction produces the wrinkles, but the claim that they necessarily evolved for wet gripping remains an unsettled functional explanation. Knowing a mechanism is not the same as proving its purpose.

https://pubmed.ncbi.nlm.nih.gov/12635117/
https://pubmed.ncbi.nlm.nih.gov/34288934/
https://pubmed.ncbi.nlm.nih.gov/24416318/