The Biological Reason Your Fingers Wrinkle In Water (And Why It Makes A Lot Of Sense)

A few days ago, my little daughter, just out of the pool, came running to look for me very worried because “she had become a pupa”. One fascinating thing about having young children is that they are a continual opportunity to rediscover the world we live in: “the pupa” was their wrinkled fingers. For me, the explanation was obvious: it is something that happens when you spend a lot of time in the water, but at that moment I realized that I did not know why.

After all, it is not that all the skin is wrinkled, no. It only occurs in the hands and feet. As Richard Gray said, “where delicate spirals of a slightly rigid epidermis were once seen, thick folds of flesh more typical of the skin of a raisin appear now”. The curious thing, if you will allow me the expression, is that as soon as one begins to investigate the matter, he discovers that there is a lot of material to cut.

A question with a long history. Searching the scientific bases, the first works that suspected that there was a cat behind such a natural process are from 1935. Until then, the most common theory explained the matter as an evident consequence of the water flooding the cells of the superficial layers of the skin. Come on, pure osmosis: water passing through cell membranes to balance the concentrations on both sides. But it turns out not.

The first clue that this explanation did not make sense came, curiously, from patients with a median nerve injury. Track? That his hands did not wrinkle. Considering all that the median nerve does, what seemed most obvious was that the wrinkled hands were a sympathetic nervous system thing. Things got interesting.

Looking for the answer. So much so that during the 1970s this (putting your hands in hot water) began to be used to assess damage to the sympathetic nervous system – damage that can affect other things, such as the circulatory system. In-depth analyzes were not possible until 2003, but it was finally confirmed that the wrinkling was related to a significant drop in blood flow. In fact, this effect can be achieved with anesthetics and other drugs that affect the nervous system in a similar way.

However, this is not an answer. That is, it does not explain why what happens happens. Nick Davis, a neuroscientist and psychologist at Manchester Metropolitan University who has studied this in detail, told the BBC that everything suggested that our bodies are actively reacting to being in the water; that is, “it could be giving us some advantage.”

Grab me hard. The explanation of the researchers, in fact, is quite curious. After doing numerous experiments, he has come to the conclusion that “the wrinkles on our fingers can act like the treads on tires or the soles of shoes.” the wrinkles would help drain the water, “moving it away from the point of contact between the fingers and the object”. Was it an adaptation to help us grip objects and wet surfaces?

But why? What is not clear is why our ancestors needed something like this. It is clear that it can be an aid when walking on rocks and grabbing branches in humid contexts, but if that were the case, it would be reasonable to see a similar reaction in primates such as chimpanzees. Something that, everything is said, we have not been able to observe. Yes, a similar phenomenon has been found in the famous Japanese macaques that bathe in hot water, but only in them.

Some theorists have proposed that adaptation may have helped us (at the dawn of the species) to consume shellfish and the like; although the truth is that the fact that wrinkles are faster and more evident in fresh water means that there is no consensus. However, if the mysteries ended there, everything would be simpler: things like why women take longer to wrinkle than men or why psoriasis (or vitiligo) also present problems for the phenomenon remain important unknowns.

what we do know. However, what is clear is that we live in a curious tension between two sides of the spectrum: on the one hand, wrinkles improve support; on the other, they worsen sensitivity. Therefore, the sympathetic nervous system plays a key role in determining when, how and why we have to move from one state to another. So this summer, when we walk on slippery surfaces without risking our lives, we already know who we have to thank.