The Science Behind Why Your Fingers and Toes Get Pruney

By Blog Editor Susan Wells

I recently spent some quality time soaking in the hot springs pool in Salida, Colorado. After sitting there relaxing and watching the kids play, I noticed my fingers and toes were really pruney. It made me start wondering why and how this phenomena happens. Is there a reason why our skin becomes wrinkled and old-looking after soaking in water? Or is it just a side effect of getting wet?

I knew one thing – prunes turn into raisins by drying out. But we were IN the water. Our skin couldn’t be drying out in the water. It had to be soaking up the water.

Scientists once believed the same thing – that the pruning and wrinkling of fingers and toes was caused by the outermost layer of skin absorbing water. Recent studies by Kyriacos Kareklas and Tom Smulders of Newcastle University in England have showed the wrinkling comes from the nervous system constricting blood vessels in the skin.

When the blood constricts, it reduces the volume of the fingertips and pulls in the skin. So even though you feel like your fingers have swelled in the water, their volume has actually decreased.

If the nerves in your fingers are damaged or cut, your skin will no longer wrinkle in water.

But why does this happen? Is it just to give you that “just bathed” look or is there more to it? Kareklas and Smulders are working on finding the answer.

Kareklas hypothesized that wrinkled skin works the same way as tire treads on a car work – to allow the water to run off from between the fingers and the objects they are trying to pick up.

These wrinkles may have helped our ancestors pick up wet materials like gathering food in a stream or getting a better grip on wet rocks with toes.

Kareklas and Smulders experimented with marbles. They had their subjects manipulate marbles with pruney hands and with dry hands. They found it was easier to move the wet marbles from water faster when their fingers were wrinkled than not. Pruney fingers did not make a difference on how fast they could move the dry marbles.

So why aren’t our fingers and toes permanently pruney? Probably because it would diminish sensitivity and pruney skin doesn’t seem to help or hinder the manipulation of dry objects.

There is more research to be done on this topic. Do other primates and mammals have the same thing happen to their digits in water? Do the wrinkles work like tire treads or do they make the skin more sticky?

Next time you are in the bath or at the pool, try experimenting with this theory. Can you pick up slippery or wet objects easier when your fingers are pruney or smooth? What about when the object is dry? Is it easier to pick up with pruney or smooth fingers?

I smell a science fair project here…

 

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