Ask Smithsonian: Why Do We Get Prune Fingers

It was eventually determined that the wrinkling was caused by the constriction of multiple blood vessels beneath the skin and is the result of an involuntary nervous system reaction. While that explains how it happens, it didn’t offer the why.

What to Know About Pruney Fingers

Maybe you’re someone who enjoys spending so much time in the sea, a swimming pool, or even a bathtub that you turn pruney. Why not? You deserve some fun. But if you notice your fingers are wrinkly when they’re dry, you may be looking at a health problem.

What Causes Pruney Fingers?

The most common cause of pruney fingers is time spent in the water. When your hands soak for a while, your skin wrinkles like a prune. ‌

Scientists used to think that water moved into the outer layers of your skin and caused it to swell. The swelling made a larger surface area, which caused the skin to later wrinkle.

Now we know that pruney fingers are caused by shrinking blood vessels. When you soak in water, your nervous system sends a message to your blood vessels to shrink. Your body responds by sending blood away from the area, and the loss of blood volume makes your vessels thinner. The skin folds in over them, and this causes wrinkles.

It’s not fully clear why this happens, but scientists believe this process evolved so you can have a better grip when your hands are wet.

Health Conditions That Cause Pruney Fingers Without Water

Getting pruney is usually harmless, especially if it happens while you’re in the water. But some health conditions can cause pruney fingers even when your hands are dry.

Raynaud’s disease. This affects your blood circulation to your fingers and toes. When you get cold, Raynaud’s causes your blood vessels to shrink and blood to flow away from your fingertips. This causes skin to wrinkle and fingertips to turn white, red, or blue.

Dehydration. You become dehydrated when your body loses more water than you take in. One thing your body uses water for is to keep your skin healthy. When you lose too much water, your skin can start to feel less elastic and become wrinkled. This is called skin turgor.

You can test this by gently pinching your skin and pulling upward as if to form a tent. If it’s slow to snap back into place, you may be dehydrated.

Thyroid disease. Your thyroid gland plays key roles for lots of activities in your body, including digesting food and your body temperature. Not enough thyroid hormone can make your body work slowly. You might have low energy, low blood pressure, and poor circulation. An underactive thyroid can also cause fine wrinkles on your skin, rashes, and cool, pale, and dry skin.

Lymphedema. This disease causes a buildup of lymph, a fluid in your body tissue, which leads to swelling. The buildup can damage tissues under your skin. As lymphedema advances, your skin can tighten, have a leathery feel, and become wrinkly.

Wrinkly skin syndrome. This genetic disease causes wrinkling or sagging skin, poor skin elasticity, and delayed closure of the fontanelle, or soft spot on a baby’s head. It also causes growth problems, joint problems, and intellectual disability. People who have wrinkly skin syndrome have excessive wrinkly skin on their hands, fingers, and other places.

Lupus. This is a disease where your immune system attacks your tissues and cells. This can cause problems with your joints, kidneys, tendons, and skin. Some people who have lupus also have Raynaud’s disease.‌

Scleroderma. This is a disease where your immune system attacks the tissues under your skin, in your organs and blood vessels. It causes scarring and skin and tissue thickening. People who have scleroderma also often have Raynaud’s.

How to Treat Pruney Fingers

The treatment depends on the cause. If you’ve been in the water, your fingers will return to normal shortly. You can apply a lotion to your hands to ease some of the dryness.

Other health conditions that cause pruney fingers each need different treatments. These can include:

• Treating thyroid disease with thyroid hormone pills
• Easing dehydration by drinking more water
• Using compression bandages and exercise to treat lymphedema
• Taking immune-suppressing medications for lupus or scleroderma

When to See Your Doctor for Pruney Fingers

If you notice you have pruney fingers and haven’t had them in water, take note of your other symptoms. If you also have the following signs of dehydration, you should go to a hospital right away:‌

• Throwing up
• Diarrhea
• No peeing all day
• Weak pulse
• Fast pulse
• Seizures
• Confusion
• Tiredness
• Dizziness

You should see a doctor if you have skin problems and you:

• Are tired a lot
• Feel cold, especially in your hands and feet
• Have sore joints
• Are gaining weight

Your doctor can help you treat these and any other conditions that might be changing your skin.

Show Sources

Aurora Health Care: “Why Does Water Make You Wrinkle?”

Biology Letters: “Water-induced finger wrinkles improve handling of wet objects.”

Breastcancer.org: “Stages of Lymphedema.”

Current Treatment Options in Rheumatology: “Hand Impairment in Systemic Sclerosis: Various Manifestations and Currently Available Treatment.”

Harvard Health Publishing: “Cold fingers, cold toes? Could be Raynaud’s.”

NIH Genetic and Rare Diseases Information Center: “Wrinkly skin syndrome.”

NHS: “Dehydration,” “Dehydration – Illnesses & Conditions,” “Lymphoedema – Treatment.” “Lupus,” “Overview: Underactive thyroid (hypothyroidism).”

Translational Pediatrics: “Dermatologic manifestations of endocrine disorders.”

University of Florida Health: “Skin turgor.”

University of Rochester Medical Center: “Systemic Lupus Erythematosus (SLE or Lupus) – Health Encyclopedia.”

Ask Smithsonian: Why Do We Get Prune Fingers?

It’s pretty much a given that fingers and toes become wrinkly after being immersed in water, but the reasons for the wrinkling weren’t fully explained until five years ago, and even now, some would say it’s still not a settled matter.

The phenomenon has been explained away over the centuries as “an accidental side effect of wetness,” according to Mark Changizi, a theoretical neurobiologist and director of human cognition at 2AI Labs in Boise, Idaho. That is, osmosis caused the skin to become waterlogged.

But Changizi—a big thinker—wasn’t satisfied with that answer. As he was investigating the shape, function and structure of primate hands, he came across a bunch of studies—starting in the 1930s and going through the 2000s—that showed that if the nerves that fed the hands had been damaged, fingers would not wrinkle after being soaked in water.

It was eventually determined that the wrinkling was caused by the constriction of multiple blood vessels beneath the skin and is the result of an involuntary nervous system reaction. While that explains how it happens, it didn’t offer the why.

And if wrinkling was only due to osmosis, why didn’t it occur everywhere on the body? The fact that wrinkling was linked to the sympathetic nervous system (part of our innate fight-or-flight mechanism) led Changizi and his colleagues to wonder if it was an evolutionary adaptation to the wet conditions that made up the habitats of many primates and some of our ancestors.

They began with the notion that the wrinkles were potentially channels, or “rain treads,” designed to drain water off the fingertips and toes to allow a better grip—just as the tread on tires allows cars to grip the asphalt in spite of water on the roadway. Changizi decided to reverse-engineer the answer to the question, starting with trying to replicate the wrinkle patterns. It took a year to figure out the best theoretical shape, he says.

They found it by looking at the topography of mountains. Rivers bunch up at the peaks and flow down, with the divides in between acting as drainage channels. Changizi and his colleagues saw the same thing on prune fingers—the divides channeled water away, allowing for a be better grip. And it was functional: the channeling didn’t happen until at least five minutes after immersion—fast enough to be of use when it’s truly wet, but not so fast that casual contact with a liquid would kick in the extra grip.

Changizi and his colleagues published their findings in 2011, but said that more research was needed to validate their grip theory.

About a year later, Kyriacos Kareklas and his colleagues at the Centre for Behaviour and Evolution at Newcastle University tested whether people with and without wrinkly fingers could pick up and move wet marbles from one box to another. Sure enough, prune fingers were more efficient. Score one for Changizi.

But in early 2014, scientists at the Max Delbrück Center for Molecular Medicine in Berlin-Buch, Germany tried to repeat the experiment and found that having wrinkly fingers made no difference in how well or poorly someone could grip a wet or dry object.

“I don’t think either study was good,” says Changizi, who hasn’t gone back to studying pruney fingers again, but says that someone could probably do a better job of proving his theory.

A big stumbling block, however, is that no one knows whether any animal—aside from humans and macaques—gets pruney fingers.

Answers will have to come from more studies of how humans use their wrinkly fingers and toes. Changizi has the perfect subject group in mind: parkour athletes who freestyle run, roll, tumble and climb outside of gyms. Give some of them prune fingers and toes and others dry digits, he says.

Changizi predicts that those with the dry hands and feet will inevitably slip and crash. Any volunteers?

Alicia Ault is a Washington, DC-based journalist whose work has appeared in publications including the New York Times, the Washington Post and Wired. When not chasing down a story from our nation’s capital, she takes in the food, music and culture of southwest Louisiana from the peaceful perch of her part-time New Orleans home.

Why Do Fingers Prune in Water?

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• Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
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Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.

Updated on March 30, 2019

If you’ve had a long soak in a bathtub or pool, you’ve noticed your fingers and toes wrinkle (prune up), while the rest of the skin on your body seems unaffected. Have you ever wondered how it happens or whether it serves a purpose? Scientists have an explanation for the phenomenon and have proposed a possible reason for why it happens.

Why Skin Prunes in Water

The prune effect is different from true wrinkling of skin because the latter results from the degradation of collagen and elastin, making the skin less resilient. Fingers and toes prune, in part, because the layers of the skin don’t absorb water evenly. This is because the tips of your fingers and your toes are covered with a thicker outer skin layer (the epidermis) than other body parts.

However, most of the wrinkling effect is due to blood vessel constriction just below the skin. Nerve-damaged skin doesn’t wrinkle, even though it has the same composition, so the effect may be a reaction to water by the autonomic nervous system. However, the hypothesis that wrinkling is under autonomic nervous system control doesn’t account for the fact pruning occurs in cold water as well as warm water.

How the Epidermis Reacts to Water

The outer layer of your skin protects the underlying tissue from pathogens and radiation. It’s also fairly waterproof. The keratinocytes at the base of the epidermis divide to produce a layer of cells rich in the protein keratin. As new cells are formed, the old ones are pushed upward and die and form a layer called the stratum corneum. Upon death, the nucleus of a keratinocyte cell involutes, resulting in layers of a hydrophobic, lipid-rich cell membrane alternating with layers of hydrophilic keratin.

When skin soaks in water, the keratin layers absorb water and swell, while the lipid layers repel water. The stratum corneum puffs up, but it’s still attached to the underlying layer, which doesn’t change size. The stratum corneum bunches up to form wrinkles.

While the water hydrates skin, it’s only temporary. Bathing and dish soap removes natural oils that would trap the water. Applying lotion can help lock in some of the water.

Hair and Nails Get Soft in Water

Your fingernails and toenails also consist of keratin, so they absorb water. This makes them softer and more flexible after doing the dishes or bathing. Similarly, hair absorbs water, so it’s easier to over-stretch and break hair while it’s damp.

Why Do Fingers and Toes Wrinkle?

If pruning up is under nervous system control, it makes sense that the process serves a function. Researchers Mark Changizi and his colleagues at 2AI Labs in Boise, Idaho, demonstrated that wrinkled fingertips provide improved grip on wet objects and that the wrinkles are effective at draining away excess water under damp conditions. In one study, published in Biology Letters, subjects were asked to pick up wet and dry objects either with dry hands or after soaking them in warm water for half an hour. Wrinkles didn’t affect the participants’ ability to pick up dry objects, but the subjects picked up wet objects better when they had pruned hands.

Why would humans have this adaptation? Ancestors who got wrinkled fingers would have been better able to gather wet food, such as from streams or beaches. Having wrinkled toes would have made barefoot travel over wet rocks and moss less risky.

Do other primates get pruney fingers and toes? Changizi e-mailed primate labs to find out, eventually discovering a photograph of a bathing Japanese macaque monkey that had wrinkled fingers.

Why Aren’t Fingers Always Pruned?

Since wrinkled skin offered an advantage manipulating damp objects yet didn’t hinder abilities with dry ones, you may be wondering why our skin isn’t always pruned. One possible reason might be that wrinkled skin is more likely to snag on objects. It’s also possible that wrinkles diminish skin sensitivity. More research could give us additional answers.

Sources

• Changizi, M., Weber, R., Kotecha, R. & Palazzo, J. Brain Behav. Evol. 77, 286–290. 2011.
• Kareklas, K., et al. “‘Water-Induced Finger Wrinkles Improve Handling of Wet Objects.’” Biology Letters, The Royal Society.