Why do our fingers go wrinkly in the pool?
A plain-English answer for grown-ups of kids aged 6–9, taken from the Yufena lesson that explores this question.
This is a members' lesson. Four other lessons are free to try.
The answer, for parents
Short answer: Nerves sense the water and tell the blood vessels to narrow, so the skin puckers into wrinkles.
Look under the skin of your fingertip. There are tiny blood vessels full of blood. There are also nerves that send messages to your brain. When your fingers stay wet, the nerves sense the water. They send a message: squeeze! The blood vessels get narrower. The fingertip shrinks a little, so the skin puckers into wrinkles.
Scientists think wrinkles help us grip wet things. They work a bit like tyre treads. Scientists are still studying this. Some tests found wrinkly fingers pick up wet marbles faster. Here is a fun fact. A finger with hurt nerves does not go wrinkly. So the nerves must be doing the job!
In the lesson, your child puts this cause-and-effect chain in order: Fingers stay wet → Nerves sense the water → Blood vessels narrow → Fingertips shrink a little → The skin puckers into wrinkles.
What if we stay in the water a very long time? The wrinkles stay while you are wet. After you dry off, they smooth out again in a little while.
Do our toes go wrinkly too? Yes. Toes have nerves and blood vessels too. Hands and feet are the parts we use to grip.
Try it with your child
Let's test grip. Put ten marbles in a bowl of water. Move them to a cup, one at a time, with dry fingers. Ask a grown-up to time you. Now soak your fingers in warm water until they go wrinkly. Move the marbles again. Which time was faster? Scientists test things just like this!
Safety: Safety first: marbles are not for little children. A grown-up should watch.
Explore it together in the full lesson
Guess, find clues, build the chain and try the experiment. Read it together.