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Mysteries of the Human Body
It used to happen: you get out of a lake or bathtub after a long swim — and instead of normal fingers you have some wrinkled “raisins”. The skin has tightened so much that it seems the hands have aged in half an hour. Why does this even happen?
For a long time it was thought that the culprit was the outer layer of skin — the epidermis. It contains keratin and absorbs water like a sponge. The outer layer swells, while the tissues beneath remain almost unchanged. Because of this difference the skin folds into creases and wrinkles.
But later it turned out: it's not only about water, but about the nervous system's work. The effect is driven by the sympathetic nervous system — the very one that helps the body react quickly to changes around it.
When the hands stay in water for a long time, the nervous system orders the blood vessels in the fingers to constrict. The finger pads shrink slightly in volume, and the skin on top begins to wrinkle. That's why people with nerve damage can have smooth fingers even after prolonged water exposure.
There is another curious detail: the wrinkles appear each time in the same pattern. In one study participants held their hands in warm water for about half an hour, after which scientists photographed their fingers. After a day the experiment was repeated — and it turned out that the pattern of folds matched almost exactly.
Why nature invented this mechanism at all remains unclear. One popular theory suggested that wrinkled fingers help grip wet objects better and prevent slipping on moist surfaces. This could have been useful to our ancestors during rain or when crossing rivers.
However, modern experiments have not found any special advantages: wrinkles on the fingers hardly improve grip, sensitivity, or hand dexterity. So for now this strange effect remains one of the small mysteries of the human body.
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