Dear health-conscious friends,

You’ve probably noticed it after a long bath, a swim, or even an enthusiastic session washing the dishes.

Your fingertips start off smooth. Then, after several minutes in water, they become covered in deep little ridges and wrinkles.

For years, the usual explanation was simple: your skin absorbs water, swells up, and wrinkles.

It sounds perfectly reasonable.

But it’s not the real explanation.

Your nervous system is doing it on purpose

The wrinkling of your fingers and toes in water is actually an active response controlled by your nervous system.

When your hands or feet stay wet for several minutes, your autonomic nervous system — the part that controls automatic functions such as sweating, heart rate and blood-vessel diameter — causes tiny blood vessels beneath the skin to constrict.

As these vessels narrow, the volume of tissue beneath the skin decreases.

The outer skin doesn’t shrink with it, so it buckles into the familiar peaks and valleys we recognise as “pruney fingers.”

And there’s a fascinating piece of evidence for this.

If the nerves supplying a finger are severely damaged, that finger may not wrinkle normally in water.

In fact, doctors have historically studied water-induced wrinkling as a simple way of assessing certain types of nerve function.

But why would your body do this?

This is where things get even more interesting.

Scientists have suggested that wrinkled fingertips may give us better grip in wet conditions.

Think of the grooves in a car tyre.

When a tyre travels over a wet road, the grooves help channel water away from the surface, allowing more of the tyre to make contact with the road.

Wrinkled fingers may work in a somewhat similar way.

The channels created by the wrinkles could help move water away from the points where your fingertips touch an object.

In experiments, people with wrinkled fingers have sometimes been able to handle wet objects more efficiently than people whose fingers were still smooth.

That raises an intriguing evolutionary possibility.

For our ancestors, better grip in wet environments might have made it easier to collect food from streams, handle wet plants, climb over slippery surfaces or maintain footing in rain and mud.

Interestingly, the effect is mainly seen on the fingers and toes — exactly where extra traction would be most useful.

So why aren't our fingers wrinkled all the time?

Because there may be a downside.

Wrinkles could interfere with normal sensation or make manipulating dry objects slightly less efficient.

So rather than permanently changing the structure of our fingertips, the body appears to switch the wrinkling response on when prolonged contact with water makes it potentially useful.

Once you leave the water, the blood vessels return toward their normal diameter and your fingers gradually become smooth again.

The next time you're in the bath...

Take a look at your fingertips.

Those wrinkles aren't simply soggy skin.

They are the visible result of your nervous system changing the blood flow beneath your skin — and they may represent an ancient biological trick for helping humans grip things when the world gets wet.

Sometimes even something as ordinary as a wrinkled finger has a surprisingly clever story behind it.

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​AskADoc Weekly: Clear medical insights without the jargon.

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👩‍⚕️ Dr. Joanna​
​AskADoc4Advice — where medicine meets curiosity (and a little bit of weird).

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