If you spend more than a few minutes splashing in the shower or pool, your fingers will change dramatically.

Where previously there were delicate spirals of slightly hard epidermis, now the raisin peel has plump folds.

The shocking change is familiar but still frustrating.

Only the skin of our fingers and toes becomes wrinkled when submerged in water, while other parts such as our forearms, torso, legs and face remain as smooth as when submerged in water.

• To drink or not to drink coffee? You decide

This way of wrinkling the skin of our fingers has occupied the minds and work of scientists for decades.

Many have been interested in understanding what causes wrinkles, but recently the question of why and what their purpose is has attracted the attention of researchers.

But what our wrinkled fingers can reveal about our health may be even more interesting.

folds, folds

In lukewarm water (40 degrees Celsius is considered the optimum temperature) it takes about 3.5 seconds for your fingers to start wrinkling, in colder temperatures, about 20 degrees Celsius, it can take up to 10 minutes.

Most studies have found that it takes about 30 minutes in water to achieve maximum wrinkling.

It was generally believed that toe wrinkling was a passive reaction in which the upper layers of the skin swell as water flows into the cells through a process known as osmosis: a process in which water molecules pass through a membrane to equalize the concentration of solutions above it. both sides of the dice itself.

But as early as 1935, scientists suspected there was something beyond this entire process.

Doctors examining patients with injuries in which the median nerve (one of the main nerves running down the arm) was severed found that the patients’ fingers did not wrinkle in the water.

Among its many roles, the median nerve helps control sympathetic activities such as sweating and blood vessel constriction.

The discovery suggested that the wrinkling movement of the fingers in the water was controlled by the nervous system.

Blood flow

Further studies by physicians in the 1970s provided further evidence for this finding and suggested the use of immersion of the hands in water as a simple test to assess the extent of some type of nerve damage that could affect the regulation of processes. unconscious as blood flow.

Then, in 2003, neurologists Einar Wilder-Smith and Adeline Chow, then working at Singapore’s National University Hospital, measured the blood circulation of volunteers’ hands immersed in water.

They found that as the skin on the fingertips began to wrinkle, blood flow to the fingers dropped significantly.

They found that when they used a local anesthetic cream that causes temporary constriction of blood vessels in the fingers, a similar level of wrinkling occurs when immersed in water.

“It makes sense to watch your fingers when they’re wrinkled,” says Nick Davis, a neuroscientist and psychologist at Manchester Metropolitan University who studies how fingers wrinkle.

“The tips of the fingers are turning pale, and this is because the narrowing of the vessels pulls blood flow from the surface.”

But why?

But if wrinkling is controlled by nerves, then our body is actively reacting in the water.

“That means it happened for a reason,” Davis says. “And that means it could give us an edge.”

Davis measured how much force it takes to grasp a plastic object with the help of 500 volunteers who visited the Science Museum in London in 2020.

Perhaps unsurprisingly, those with dry, wrinkle-free hands had to use less force than those with wet hands because they grasped the object better.

But when they immersed their hands in the water for a few minutes, their grip strength dropped, even though both groups were still wet, until their hands were wrinkled.

“The results were incredibly clear,” Davis said.

• Anemia in children: what are its symptoms and how to prevent it?

“The wrinkles increased the friction between the fingers and the object. What is particularly interesting is that our fingers are sensitive to this change in surface friction, and we use this knowledge to apply less force while holding an object securely.”

Their findings agree with those of other researchers who found that the wrinkles on our fingers make it easier for us to grasp wet objects.

Some scientists have suggested that the wrinkles on our fingers may act like lines on rubbers or on the soles of shoes.

The channels that create wrinkles help water away from the point of contact between the fingers and the object.

This suggests that finger wrinkles may have evolved at some point in the past to help us grasp objects and wet surfaces.

And for what?

“Since it seems to give us a better grip underwater, I can assume it has to do with either moving in very wet conditions or potentially manipulating objects underwater,” says Tom Smulders, an evolutionary neuroscientist at Newcastle University who led the 2013 study.

For example, it could have given our ancestors a significant advantage when they had to walk on rocks or grab hold of branches.

Alternatively, it may have helped us catch food such as shellfish.

“If the explanation is the latter, it means it’s a uniquely human trait, whereas if it isn’t, we would expect to see it in other primates,” Smulders says.

other species

We haven’t yet seen wrinkles on the fingers of species closest to us in the primate world, such as chimpanzees, but Japanese macaques, which are known to bathe in hot water for a long time, have also had wrinkles on their fingers. after immersion in water.

But the lack of evidence doesn’t mean it won’t happen, perhaps because no one has looked closely enough, Smulders says.

“We don’t know the answer to that question yet.”

There are other interesting clues as to when this adaptation might have evolved in our species.

Finger wrinkling is less noticeable in saltwater and lasts longer than in freshwater. This probably occurs because the salt gradient between the skin and the surrounding environment is lower in salt water, so the salt imbalance that signals nerve fibers is less dramatic.

So it may have been an adaptation that helped our ancestors live in freshwater rather than coastal areas.

But there are no definitive answers, and some believe it may be a physiological response that arose by chance without any adaptive function.

more questions

Oddly enough, there are other mysteries: For example, women’s wrinkles last longer than men.

And if there’s no downside to grasping dry objects with wrinkled fingers, why does our skin return to its normal state, usually within 10 to 20 minutes?

If having wrinkled fingers improves our grip in water and doesn’t hurt when dry, why don’t our fingers always stay wrinkled?

One reason may be the change in sensation caused by wrinkles. The tips of our fingers are full of nerve endings, and wrinkles on our fingers change how we feel about things we touch (although one study shows that it doesn’t affect our ability to distinguish objects based on touch).

But wrinkling our fingers in water can also reveal important information about our health in surprising ways.

For example, people with skin conditions such as psoriasis and vitiligo are also slower to form wrinkles.

Cystic fibrosis patients experience excessive wrinkles on their palms as well as their fingers. Patients with type 2 diabetes also report that wrinkling levels are significantly reduced when their hands are immersed in water.

Similarly, people with heart failure have seen reduced wrinkles, perhaps due to some deterioration in the control of their cardiovascular system.

• Five truths and falsehoods to reach the ideal weight

Even asymmetrical wrinkling of the fingers, in which one hand is less wrinkled than the other despite being in the water for the same amount of time, has been suggested as an early sign of Parkinson’s disease enough to indicate a dysfunction of the sympathetic nervous system. one side of the body is not working properly.

So while the question remains why our fingers and toes start to wrinkle in the first place, our aging fingers are useful in medicine in surprising ways.