Why does skin wrinkle in water?
The short answer
After fingers stay in water for a while, wrinkling is linked to constriction of blood vessels in the fingertips and reduced local blood flow, a response involving sympathetic nerves. It is not explained by the outer skin swelling alone.
How it works
Some experiments found that wrinkled fingers handled submerged objects faster or needed less force to grip wet objects. Another experiment found no improvement in dexterity or touch. Whether the wrinkles help with grip appears to depend on the task and conditions.
A familiar example
Water-induced wrinkles also occur on non-hairy skin, including the fingers, palms, and soles. Blood-vessel changes are linked to the response, but the full process is not yet understood.