I figure if I want to know the answer to something I must not be the only one out there with the same question. Lately I’ve been thinking – how come our hands and feet wrinkle after being in the water for a long time? The reason for that is actually quite simple:
The epidermis is the uppermost (and outermost) layer of the skin. … The middle layers of the epidermis are where cells release substances including lipids (fats) that help keep the cells and skin as a whole hydrated. (If you’ve ever wondered why your fingers and toes get wrinkly after being in the water, it’s because these areas produce less fats, which makes them less “water-tight”).
The wrinkles that develop on wet fingers could be an adaptation to give us better grip in slippery conditions, the latest theory suggests.
The hypothesis, from Mark Changizi, an evolutionary neurobiologist at 2AI Labs in Boise, Idaho, and his colleagues goes against the common belief that fingers turn prune-like simply because they absorb water.
Changizi thinks that the wrinkles act like rain treads on tyres. They create channels that allow water to drain away as we press our fingertips on to wet surfaces. This allows the fingers to make greater contact with a wet surface, giving them a better grip. …
When we press down with a finger, we apply pressure from the tip backwards. The sides of the finger are like cliffs where water can easily fall away, but the flat part is more like a plateau where water can pool. Wrinkles form on the plateau because “that’s where all the work has to be done to channel the water away”, Changizi explains.
Not everyone is gripped by the new theory. “This hypothesis is unjustified,” says Xi Chen, a biomechanical engineer at Columbia University in New York. Chen thinks that the wrinkles have a simpler cause: when fingers are immersed in hot water, the blood vessels tighten and the tissue shrinks relative to the overlying skin. This contraction causes the skin to buckle. “It’s a classic mechanics problem,” he says.
But neurosurgeon Ching-Hua Hsieh of the Chang Gung Memorial Hospital in Kaohsiung, Taiwan, says that the process Chen describes does not account for the fact that fingers wrinkle even in cold water, or that they do not wrinkle when their blood supply is cut off. He thinks people should be looking for more explanations of water wrinkling. “I really appreciate the new hypothesis,” he says.
Hsieh and Changizi both note that water wrinkles appear only on the fingers and feet, and that the most prominent wrinkles develop at the ends of digits, which are the first parts to touch a surface.
So who’s right? Is this new hypothesis about why our fingers and toes wrinkle in the bath correct? Only time will tell.