Why Do Our Fingers Prune in the Water?
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Updated June 09, 2015.
Question: Why Do Fingers Wrinkle?
We've all seen it: take a bath or a long shower, or go swimming, and you notice the tips of your fingers wrinkle. We're used to it, but do we know why this happens? The short answer is "no." No one really understands why our fingers wrinkle, though there are some theories. At present, however, there's still significant debate about both how and why our fingers wrinkle.
Answer: There are some things we do know. The first is that, contrary to what many people think, the process of finger wrinkling cannot just be explained by osmosis. Most people think that by submerging your hands in water, the finger tips draw water in to the skin in a process known as osmosis, causing the skin to wrinkle. The truth is that, while water may cause some upper layers of the skin to swell, there's also an important role of blood vessels and nerve endings that help cause skin wrinkling.
We know osmosis does not account for finger wrinkling for a few reasons:
- First, only the skin of the fingers and toes wrinkle--osmosis would cause all skin to wrinkle if that were the explanation.
- Second, if you cut the sympathetic nerves to the fingers, they no longer wrinkle!
Nervous System
One component of finger wrinkling is involvement of the sympathetic nervous system, which is important in controlling a number of body functions, including heart rate and blood pressure. The sympathetic nervous system is the part of the nervous system known for the "fight or flight" response.
Peripheral blood vessels constrict when the sympathetic nervous system is activated, to divert blood to the center of the body and the major muscles and organs. The sympathetic nerve activation is thought to be the stimulus that leads to the finger wrinkling.
Blood Vessels
When the sympathetic nervous system is activated, and the blood vessels of the fingers constrict, the decreased volume in the deep layers of soft tissue essentially pull the skin in, creating the folds that we know as wrinkles.
It's interesting that immersing your hand in warm water causes the finger blood vessels to constrict. Again, many people would expect the blood vessels to dilate — our body's normal response to warmth.
Why Do Fingers Wrinkle?
Again, there is an ongoing debate about why our bodies have developed this ability to wrinkle the skin.
The most recently proposed theory is that skin wrinkling allows for better ability to grip objects with wet fingers. By creating "treads" similar to tire treads, the fingers have been shown to grasp wet objects better once the wrinkling response has occurred.
The wrinkle pattern of fingers has been studied, with researchers finding that it works to funnel water away from the skin, allowing a better grip on wet objects. Researchers also found that those people whose skin has had time to wrinkle were better able to handle wet objects. The researchers think that the reason wrinkling only occurs on hands and the feet is the importance of grip, and therefore why the rest of the body does not wrinkle when immersed in water.
This is one recent theory, and it certainly has a lot of people thinking they've solved the problem. But this isn't the first theory proposed to explain finger wrinkling, and it may not be the last.
Sources:
Changizi M, et al. "Are wet-induced wrinkled fingers primate rain treads?" Brain Behav Evol. 2011;77(4):286-90. Epub 2011 Jun 23.
"Getting a Grip on Finger Wrinkles" Science Friday. Jan. 11, 2013.