Why Do Our Fingers Turn Prune-like?

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Do you ever take an extra long shower (okay, I know, California is in a drought, but sometimes it is relaxing) and realize that your fingertips are wrinkley and look like prunes? This happened to me today and I have never thought about the scientific reason behind this phenomenom. From my limited biology knowledge, I assumed it has something to do with osmosis and being exposed to water for a long period of time causes our fingertips to become hypertonic, and therefore "shrink." However, why does this not happen with the rest of our bodies? Is my logic even correct?

It is interesting to see that there is still no real evidence behind the explanation of the wrinkled finger phenomenom. However, studies suggest that the real reason for the wrinkled finger phenomenom is that blood vessels just under the skin constrict as an involuntary nervous system reaction to skin’s immersion in water. This causes the upper layers of skin to pucker and wrinkle. Scientists observed people whose fingers are nerve-damaged and discovered that their fingers did not prune up.

But why does this happen? A study conducted in 2013 by the Newcastle University in England showed that wrinkled fingers do improve the handling of wet objects. However, a separate study conducted in 2014 by the Max Delbrück Center for Molecular Medicine in Berlin, Germany disproved this claim and found no such effect.

So, until scientists figure this one out, I'll continue observing the ebbs and flows of my pruney fingers and be fascinated with the human body.