Why Do We Wrinkle When Wet?

Whether you’re swimming or washing the dishes
or just taking nice, long, well-deserved bath — if you’re immersed in water for longer
than 10 minutes, chances are your fingers and toes will emerge looking like raisins. So what’s up with the wrinkled digits? For years, scientists thought the phenomenon
was the result of a type of osmosis, caused by water passing into the dry outer layer
of skin. The influx of water, the thinking went, would
expand the skin’s surface area, but not the tissue below it, so the skin would bunch
up and wrinkle. But in 1935, a pair of doctors noticed that
this effect didn’t happen in their patients with nerve damage. One patient, for example, was a boy who had
lost the feeling in three of his fingers. The researchers found that, when his hand
got wet, the fingers that he could feel wrinkled as normal, but the ones that were numb remained
smooth. It turned out that pruney digits weren’t
caused just by the passive flow of water through the skin — it was an active response of the
nervous system to prolonged moisture. The nervous system causes the wrinkling by
constricting blood vessels below the skin, which causes the upper layers of skin to pucker. Since the phenomenon is caused by an involuntary
nerve response, some biologists have thought that it must have some evolutionary function. But what possible purpose could it serve? One recent theory suggests that wrinkly skin
may have given our ancestors a better grip while working in wet conditions — like gathering
food from a stream or damp vegetation. And it may also have given us better footing while
walking across slippery landscapes in the rain. In a 2013 study, evolutionary biologists tested
this theory by asking subjects with either wrinkly and non-wrinkly fingers to pick up
a variety of wet and dry objects, like marbles. They found that the subjects with wrinkly
digits picked up the wet objects 12 percent faster than their counterparts. But there
was no difference when it came to picking up dry objects. The wrinkles apparently helped channel the
water away, much like the treads on your car’s tires. But then this raises the question: If wrinkly
skin gives us a better grip, then why isn’t our skin wrinkly ALL of the time? Well, maybe because shriveled fingers and
toes are less sensitive, which is no advantage at all. Thanks for asking! And if you’d like to
submit questions for us to answer, or get these Quick Questions a few days early, check
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