Here at Seeker World Headquarters -- actually a leased S.H.I.E.L.D. Helicarrier currently hovering over Detroit -- we're committed to exploring all areas of science. Consider, for instance, the enduring mystery of pruney fingers. Amy Shira Teitel investigates in today's DNews report.
It's one of those questions that inevitably occurs to kids during bath time: Why do our fingers and toes get wrinkly when they're wet? It all starts with the skin, which has three layers: subcutaneous tissue on the bottom, the dermis in the middle, and the epidermis on the outside. The epidermis, in turn, has four layers, including the outermost stratum corneum.
A common but inaccurate belief regarding pruney fingers is that water somehow swells the skin -- specifically the stratum corneum -- causing it to wrinkle and fold. This seems reasonable, except that people with certain kinds of nerve damage don't get wrinkly fingers in water.
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Scientists have been looking into this since at least the 1930s, and have made some interesting discoveries. It seems that skin wrinkling is actually an active function of the sympathetic nervous system. This strongly suggests that pruney fingers and toes are an evolved trait that bestow some kind of advantage. The skin isn't just swelling up -- it's wrinkling for a reason.
In 2011, researchers noticed that folded skin seems to create a kind of drainage system to get water off the fingertips, so they ran some tests to see if the phenomenon actually improves grip. Sure enough, pruney fingers were found to have signature properties of drainage networks, enabling efficient removal of water from the gripped surface.
A second series of experiments in 2013 took the idea further. Participants were asked to pick up wet and dry objects like marbles with dry hands, then try again after their hands had been soaking in warm water for 30 minutes. Across the board, participants were able to pick up wet objects faster with wrinkly fingers, suggesting that the trait is ineed designed to give us better grip.
The studies were too small, in terms of sample size, to be really conclusive. But they clearly suggest that wrinkly fingers are an acquired evolutionary trait, especially since the phenomenon is triggered by the sympathetic nervous system.
Our work here is done. For more probing inquiries and full episodes from the Discovery Channel, click on over to Discovery GO.
-- Glenn McDonald
Scientific American: Why Do Our Fingers and Toes Wrinkle During a Bath?
NCBI: Water immersion wrinkling--physiology and use as an indicator of sympathetic function
Nature: Science gets a grip on wrinkly fingers