Stay in the bath long enough and your fingertips turn into little prunes. Most people think the skin simply soaks up water and swells. The real answer is more interesting: your nervous system is doing it on purpose.
It is your nerves, not just the water
Doctors have known since the 1930s that fingers with damaged nerves do not wrinkle in water. That was the first clue. If wrinkling were only about skin soaking up water, nerves would not matter.
Today we know the wrinkles come from the autonomic nervous system, the automatic system that also controls your heartbeat, breathing and sweating. After a while in water, it makes the small blood vessels under the skin of your fingertips narrow. The soft tissue shrinks a little, and the skin on top folds into ridges.
The tyre tread idea
In 2011, scientists suggested that the ridges could work like the tread on a car tyre in the rain, giving water a path to drain away so the finger can grip better.
In 2013, a team at Newcastle University in the UK tested this. Twenty volunteers moved wet marbles and small weights from one container to another, once with normal fingers and once after soaking their hands in warm water for 30 minutes. With wrinkled fingers, they moved the wet objects about 12% faster. With dry objects, wrinkles made no difference.
So why are our fingers not always wrinkled?
The researchers were not sure. One idea is that permanent wrinkles could make fingertips less sensitive, or more likely to catch on things. Smooth when dry and ridged when wet may simply be the best of both worlds.
Scientists still debate how much the wrinkles really help, and later studies have not all agreed. But one thing is clear: pruney fingers are an active response from your body, not just wet skin.
In short
- Water-wrinkled fingers are controlled by your nervous system.
- Blood vessels under the fingertips narrow, and the skin folds into ridges.
- In one study, wrinkled fingers handled wet objects about 12% faster.
Sources
- Kareklas et al. (2013), Biology Letters: Water-induced finger wrinkles improve handling of wet objects
- Scientific American: Why do our fingers and toes wrinkle during a bath?
- Science News: Pruney digits help people get a grip
This article is for curiosity and learning only and is not medical advice.