Pruney fingers

How it works

The old explanation is that the outer skin absorbs water and swells. This is wrong¹. The evidence is simple: fingers with damaged nerves do not wrinkle, even after a long soak. Doctors once used this as a test for nerve damage¹. Soaking alone is not enough.

Wrinkling is an active response. The sympathetic nervous system tightens the blood vessels in the fingertip. The volume of tissue under the skin drops. The skin, anchored to the tissue below, folds into ridges¹². Wrinkles start after about 5 to 15 minutes in water, and warm water works faster than cold¹. They fade after you dry off.

Why the body does this is still debated. In 2011, researchers proposed that the wrinkles work like tyre treads, channelling water away so the fingertip can grip a wet surface¹. A 2013 study tested it. People moved wet marbles between containers faster with wrinkled fingers, and there was no difference with dry objects¹. Later studies found mixed results, so the tread idea is likely but not settled¹.

Try it

1. Put one hand in a bowl of warm water for 10 minutes. Keep the other hand dry.
2. Compare the fingertips.
3. Drop some marbles or coins into a second bowl of water. Pick them out with each hand and time yourself.
4. Dry both hands and watch the wrinkles fade.

History and culture

The osmosis story appears in many school textbooks and is still widely believed. The nerve link was noticed in the 1930s by surgeons treating hand injuries, but the idea that wrinkling is an active response took decades to spread¹.