Appliance of science: Why do our fingers wrinkle in the bath?

Scientist Dr Naomi Lavelle explains why our fingers wrinkle when they’re wet

Why do our fingers wrinkle in the bath?

This question comes in from nine-year-old Emily, who lives in Dublin and loves science, exploring and asking her mum lots of questions!

It happens to us all, a long soak in the bath, or too long spent washing dishes and our fingers wrinkle up like raisins.

It doesn’t hurt and it doesn’t last long, but why does it happen at all?

Until recently scientists thought it might simply be due to osmosis (the process where water travels across a semi permeable membrane from a solution of low concentration, to a solution of high concentration).

The water would move through the skin into the upper layer of cells, causing them to swell.

There were many holes in this semi-permeable theory (sorry, I couldn’t resist that pun).

We now know that this osmosis theory is not the answer. The process does not work in people when certain nerves are damaged or severed.

One particular example was a small boy with nerve damage to just three of his fingers; When his hand was placed in water for an extended time those three fingers remained unwrinkled, while the two other were wrinkled as expected.

These observations led to the conclusion that skin wrinkling is controlled by the body’s nervous system. It is not under our conscious control.

Signals from the brain cause blood vessels under the skin to constrict, causing the upper layer of skin to pucker and wrinkle.

When does it happen and when does it disappear?

Luckily, this skin wrinkling process doesn’t happen straight away. If it did, we would be turning to prunes every time we touched water.

It takes about five minutes of continuous exposure to water before the wrinkles appear. That is with fresh water. In salty water the process takes even longer.

Once we remove our skin from the water the process reverts very quickly.

What parts of our bodies are affected?

It is not an all over body response. The areas affected are the fingers, palms of the hands, toes and soles of the feet.

If we look at what these parts of the body have in common we start to get an idea of why it happens.

Although there are still many question yet to answer, scientists agree that the process has something to do with our grip. Considering that the areas affected are parts of the body used for gripping, then this theory seems a sound one.

Is the wrinkle pattern random?

The wrinkle patterns created on our skin are arranged in a very specific way. They allow water to collect and run off, improving our grip. These wrinkles act in the same was as threads on a tire or natural river drainage systems.

Why is grip so important?

Scientists are still working on this one. There are studies that show that these wrinkled fingers allow us handle wet objects more easily, but there are other studies that say the opposite. It does seem that this is an evolutionary process. Maybe it evolved to help us gather food more easily in wet conditions; maybe it gave our feet better footing in the rain or maybe it was simply an advantage in climbing trees while supporting our body weight.

Why is the process not permanent?

In dry conditions smooth is best! Wrinkled skin also gives us less sensitivity and possibly increases our risk of damage or injury.

So now you know why our skin wrinkles, just don’t try to use it as an excuse to get out of doing the dishes!

Naomi is a science communicator and mother to three inquisitive children. She loves exploring life through the questions children ask. She can be found at sciencewows.ie. drhowsciencewows@gmail.com

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