Curious Kids: why do our toes and fingers get wrinkly in the bath?

If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au.

Why do our toes and fingers get wrinkly in the bath? – Jade, aged almost 4.

Thanks for your question, Jade.

The truth is scientists aren’t exactly sure why our fingers and toes get wrinkly in the bath.

Here’s what we do know:

• it happens when we stay in the bath for more than about five minutes, but can happen faster if the water is hotter. In warm water (about 40 degrees Celsius), the skin on your hands and feet can wrinkle in only 3.5 minutes
• it also happens to macaque monkeys
• it only happens on our hands and feet. The rest of our skin doesn’t tend to wrinkle in this way.

We do know the water doesn’t just leak into our fingers all by itself. The body actually works to let the water past the first few layers of skin. It has something to do with our nervous system, the network of “wires” that help pass messages from your brain to various parts of your body.

In fact, if you cut or damage certain nerves, the skin on hands or feet won’t wrinkle when wet.

And we also know the wrinkling has something to do with blood vessels shrinking. Blood vessels are the tiny pipes that carry blood around your body. Veins, arteries and capillaries are all types of blood vessels.

So we have some clues about how the skin wrinkles, but no clear answer on why.

Even though we don’t really understand why this wrinkling happens, there are some theories. Theories means scientists have come up with their best guesses.

Good grip in a slippery situation?

Have you found things that are wet are easier to pick up when your hands are wrinkly?

Some scientists think wrinkling may give us better grip in water. This makes it easier for us to touch and hold wet objects with our hands. Our toes also wrinkle in water, and so maybe this helps us safely walk on wet surfaces.

A very long time ago, this would have helped our ancestors collect food from underwater, especially in fast-flowing water like you might see in a creek or river.

However, some scientists tested this idea, and found having wrinkled fingers often did not help. So maybe this isn’t the answer after all.

Why aren’t our fingers always wrinkly?

If there are some good things to do with wrinkly fingers and toes, why aren’t they always this way?

Well, wrinkles might make it easier for our skin to get injured or make it harder to feel sensations. And if your feet are wet and wrinkly all the time you might get a painful and dangerous condition called trench foot.

So maybe wrinkly hands and feet aren’t something you want all the time.

Your question is a very interesting one that scientists still wonder about. Maybe one day you will find the answer.

Christian Moro does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.