What do the wrinkles on our fingers reveal about our health when they get wet?

If you spend more than a few minutes in the shower or splashing around in a pool and your fingers will have a dramatic transformation.

Where once delicate spirals of epidermis slightly stiff now there are a few plump folds of raisin skin.

The shocking change is familiar, but still unnerving.

Only the skin on our fingers and toes wrinkles when we dip it in Waterwhile other parts such as our forearms, torso, legs and face remain just as smooth as when they entered the water.

Photo: Getty Image via BBC

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

Many have been concerned with understanding what causes wrinkles, but more recently, the question of why, and what their purpose is, is attracting the attention of researchers.

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

folds, folds

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

Most studies have found that approximately 30 minutes in the water is required to achieve maximum wrinkling.

It was commonly believed that toe wrinkling was a passive response in which the upper layers of the skin swelled as water flooded into the cells through a process known as osmosis: a process by which water molecules They cross a membrane to equalize the concentration of solutions on both sides of the membrane itself.

But as early as 1935, scientists suspected that there was something further to this whole process.

Doctors studying patients with injuries in which the median nerve (one of the main nerves that runs through the arm and down to the hand) had been severed found that the patients’ fingers did not wrinkle in the water.

Photo: Getty Image via BBC

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

The discovery suggested that the wrinkling action 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 proposed using immersion of the hands in water as a simple test to assess the extent of a type of nerve damage that can affect the regulation of processes. unconscious as blood flow.

Then, in 2003, neurologists Einar Wilder-Smith and Adeline Chow, working at the National University Hospital in Singapore at the time, 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.

When they used a local anesthetic cream that caused blood vessels in the fingers to temporarily constrict, they found that similar levels of wrinkling occurred as during immersion in water.

“It makes sense when you pay attention to your fingers when they wrinkle,” says Nick Davis, a neuroscientist and psychologist at Manchester Metropolitan University who has studied how fingers wrinkle.

“The tips of the fingers turn pale and it is because the constriction of the vessels is withdrawing the blood supply from the surface.”

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But why?

But if the wrinkling is controlled by nerves, it means our bodies are actively reacting to being in the water.

“That means it’s happening for a reason,” says Davis. “And that means it could be giving us an advantage.”

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

Perhaps unsurprisingly, those with dry, unwrinkled hands had to use less force than those with wet hands, because the grip on the object was better.

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

“The results were incredibly clear,” Davis said.

“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 that we use this information to apply less force when gripping an object safely.” .

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

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

The channels that produce the wrinkles help to drain the 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 our past to help us grasp objects and wet surfaces.

And for what?

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

It could have given our ancestors a key advantage when they had to walk on rocks or grab branches, for example.

Alternatively, it may have helped us catch food like shellfish.

“If the explanation is the latter, it would imply that it is a feature unique to humans, whereas if not, we would expect to see it in other primates as well,” says Smulders.

Photo: Getty Image via BBC

Other species

We haven’t yet seen the wrinkles on the fingers of the species closest to us in the primate world, such as chimpanzees, but the fingers of Japanese macaques, who are known to bathe in hot water for long periods, are also have seen wrinkling after being submerged in water.

But just because there’s a lack of evidence doesn’t mean it won’t happen, it may just be that no one has looked closely enough, says Smulders.

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

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

Finger wrinkling is less noticeable in salt water and takes longer than it does in fresh water. 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 be an adaptation that helped our ancestors to live more in fresh water than in coastal areas.

But there are no firm answers, and some believe it could simply be a physiological response that arose coincidentally, without any adaptive function.

More questions

Strangely, there are other mysteries: It takes women longer to develop wrinkles than men, for example.

And why does our skin return to its normal state, usually within 10 to 20 minutes, if there is no disadvantage in gripping dry objects with wrinkled fingers?

If having wrinkled fingers can improve our grip in the water, and not 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 the wrinkles on our fingers change the way we feel about the things we touch (although one study has shown that it doesn’t affect our ability to differentiate objects based on touch).

But the wrinkling of our fingers in the water can reveal important information about our health in surprising ways, too.

Wrinkles are also slow to form in people with skin conditions like psoriasis and vitiligo, for example.

Cystic fibrosis patients experience excessive wrinkling of their palms as well as their fingers. Patients suffering from type 2 diabetes also report markedly reduced levels of wrinkling when their hands are immersed in water.

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

Even asymmetrical wrinkling of the fingers, in which one hand wrinkles less than the other despite spending the same amount of time in the water, has been suggested as an early sign of Parkinson’s disease, to the extent that it indicates that the sympathetic nervous system is not working properly on one side of the body.

So while the question remains as to why our fingers and toes started wrinkling in the first place, our aging fingers are proving useful to medicine in surprising ways.

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