Why Do Fingers Prune?

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Have you ever wondered why your fingers prune after a long bath or swim in the ocean? It turns out the answer isn't what you might think it is. Find out why your fingers prune (or don't) in this lesson.

Pruney Fingers

People don't like wrinkles, but there's actually some good news regarding wrinkles. They might actually be good for you, so toss away those expensive anti-wrinkle creams!

You've surely noticed that after at least five minutes in water, your fingers and toes begin to prune (wrinkle up). But how does this happen, and why? You might answer that it has to do with water causing the pruning, or something related to the nervous system, or blood vessels constricting. However, it turns out that none of these fully explain how our fingers prune. This lesson covers what we know about this interesting puzzle of our body. First we'll discuss the theories for how pruning occurs and then we'll consider why we think it occurs.

How Fingers Prune

One common theory holds that fingers and toes prune because they become water-logged. The outermost layer of our skin supposedly absorbs water much like a sponge does, albeit more slowly. As a sponge fills with water, it expands and swells. Theoretically, as the outer layer of our skin becomes more water-logged, it also swells up in a similar fashion and forms visible ridges. But if this is the case, then why doesn't the rest of our body prune just like our fingers and toes do? This might have something to do with differences in the structure of the skin in our hands and toes versus the rest of the body. Or, there may be another explanation.

The fact that water is not the sole cause of the pruning of our fingers was discovered decades ago. Despite this, the relatively simple explanation of water causing our fingers to prune has dominated much of lay-thought for a long time. More recent evidence, however, has brought back to life the notion that the nervous system also plays a role in the pruning of the fingers.

In the 1930s, researchers discovered that people who had nerve damage associated with their hands did not experience any pruning of their fingers. But don't worry. If your fingers don't prune, that doesn't automatically mean you have nerve damage. It turns out that completely healthy people sometimes do not experience pruning of the fingers, further complicating the explanation of how and why fingers prune.

Recent studies have shown that both water and the nervous system might play a role in the pruning of fingers. Water may indeed enter into our skin and be partly responsible for pruning. As water enters the skin, it causes nerves to signal the blood vessels in our fingertips to vasoconstrict, or shrink. As the blood vessels there shrink, the volume of blood being delivered to the fingertips diminishes. This is somewhat like turning off a gardening hose; unwatered plants will shrivel and wrinkle, just as our fingertips do with a reduced supply of blood.

Wrinkled fingertips after a bath
Pruney Fingers

Why Fingers Prune

Even if this explains how our fingers prune, then why doesn't pruning happen all over the body? Again, it may be due to a difference between the structure of the skin in the hands and feet and the rest of the body, or it may be due to an evolutionary adaptation.

Some studies have shown that pruney fingers improve traction (like how ridges on a tire improve grip on a wet roadway). The ridges on human fingertips and toes helped our ancestors grip wet surfaces like river rocks, wet trees, and so on. This may have allowed early humans to run faster, better escape predators, or catch a meal. We don't grip with our elbows and back much, do we? Hence, there was no reason to evolve a pruney back or elbows.

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