Why Your Fingers Get Wrinkly in the Bath

Look at your hands in the bath

You have been in the bath for a while. You look down at your fingers.

They have gone crinkly. Little ridges and dips, all over the tips. Like raisins.

Your toes have done it too.

And then you get out, dry off, and after a while they are smooth again as if nothing happened.

What everybody says

Ask a grown-up and they will nearly all say the same thing.

Your skin soaked up the water, like a sponge. It swelled up and went crinkly.

It sounds right. It is not right.

And you can catch it out yourself, in the bath, tonight.

Your tummy was in the same water

Your fingers went crinkly. Your toes went crinkly.

Now look at your tummy. Look at your arm. Look at your knee.

All of them sat in exactly the same bath, for exactly as long. All of them are perfectly smooth.

If water soaked into skin and made it crinkly, it would do it everywhere. It doesn't. It only ever does your fingers and your toes.

Here is the part that gives it away

Inside your arm there are nerves. A nerve is like a tiny wire. It carries messages between your hand and the rest of you.

Sometimes a person hurts one of those wires. Then the hand still works a bit, but some messages cannot get through any more.

Here is the surprising thing.

When that person puts their hand in warm water, those fingers stay completely smooth. No crinkles at all. The other hand crinkles up as usual.

Same person. Same bowl. Same water. One hand crinkles and one hand doesn't.

A sponge does not care about wires. So your fingers are not sponges.

Your body is doing it on purpose

Your fingers do not get crinkly because water happened to them. They get crinkly because your body chose to.

When your fingers have been wet for a few minutes, a message goes down that little wire to your hand. And then your skin changes shape.

You did not decide it. You cannot feel it happening. But it is your own body doing it — the same way your body decides to shiver when you are cold, without asking you first.

And if the message cannot get through, nothing happens at all. That is the bit that proves it.

Now the best bit: nobody knows why

So your body does it on purpose. But what FOR?

Here is the exciting part. Nobody has worked that out yet. Not your teacher, not your doctor, not the cleverest scientist alive.

They do have a guess. Look at the bottom of a wellington boot. It has grooves in it so it holds on to wet ground. Maybe crinkly fingers hold on to wet things better.

So some scientists tested it. They gave people wet marbles to pick up. The crinkly fingers did a bit better.

Then a different lot of scientists did their own test. They found no difference at all.

The two teams do not agree. So the question is still sitting there, unanswered, on the ends of your own hands.

Somebody is going to work it out one day. It might be you.

One bath, from start to finish

Here is one hand in a warm bath. Press to see what happens next.

Crinkly, or smooth?

Everything here has been in warm water for a good while. Put each one in the right box.

Three things to keep