Why do your fingers prune in water?

Not just soggy skin

The obvious guess is that skin soaks up water like a sponge and swells. For a long time that was the standard explanation: osmotic swelling of the outermost skin layer⁵. But in the 1930s, the researchers Lewis and Pickering noticed that fingers whose nerve supply was blocked or cut did not wrinkle^{3, 6}. If wrinkling were just passive soaking, a missing nerve should make no difference. A recent review sums up their conclusion: wrinkling is an active response of the sympathetic nervous system, not simple water absorption³.

In 1973, Seamus O'Riain described a simple warm-water test of nerve function in the hand. He reported that its results matched what surgeons found during operations¹¹. Versions of this 'wrinkle test' are still studied today³.

Your fingertip deflates

In 2003, researchers in Singapore measured blood flow in volunteers' hands while they soaked them. As the skin wrinkled, blood flow in the finger arteries and skin dropped. Their verdict: wrinkling is 'a function of digit pulp vasoconstriction', a narrowing of the blood vessels in the fingertip pad¹.

Picture the fingertip pad as a cushion under a sheet of skin. When its vessels tighten, the cushion loses volume and the skin on top has to fold^{2, 5}. In a striking test with 25 volunteers, EMLA, a numbing cream that also narrows blood vessels, was put on the fingertips. It caused nearly the same wrinkling and a nearly identical drop in blood flow as soaking in water¹².

So what does the water do? It probably seeps in through the many sweat ducts of the palms and soles and changes the salt balance in the skin, which may push the nerves to tighten the vessels^{2, 3}. In a study of 14 volunteers, saltier solutions slowed wrinkling down¹⁵. Swelling is not entirely off the hook, though. A computer model found that swelling of the outer layer plus shrinking of the deeper layers creates wrinkles far more easily than either one alone¹⁰.

Timing, temperature and a repeating pattern

Warmth helps. Lewis and Pickering saw faster wrinkling in warm water and none in cold³. A 1997 study named 40°C as the best temperature for testing hands, with wrinkling expected after about 3.5 minutes⁸. Full wrinkling takes longer: many experiments soak hands for 30 minutes^{5, 6, 9}, and a review notes that most healthy people show wrinkling after 30 minutes³. It happens on the hairless skin of both hands and feet⁵.

The wrinkles are temporary. In one experiment they faded 10 to 20 minutes after people washed and dried their hands⁵. In a small 2025 study of three people, the wrinkles came back in nearly the same pattern a day or more later. The authors suspect this is because the blood vessels underneath stay in place⁹.

Built for grip? The jury is out

If the body actively makes wrinkles, could they be useful? In 2011, Mark Changizi and colleagues proposed that they work like 'rain treads', a bit like the tread on a tire: channels that drain water away when we grip something wet⁴.

In 2013, a Newcastle University team¹⁴ had 20 people move marbles and weights with smooth or wrinkled fingers. With wrinkles, moving submerged objects took 12 per cent less time, while dry objects showed no difference⁵. In 2014, a Berlin team tested 40 people with a similar task. They found no advantage and no change in touch sensitivity^{6, 13}. A 2021 study of 516 people measured grip force instead of speed. Wet, smooth fingers squeezed harder than dry ones, while wrinkled fingers gripped much like dry fingers⁷.