We’ve all had a long swim, bath or shower sometime in our lives and come out looking like a prune. Wrinkly hands, feet, fingers and toes – but why? Have you ever wondered how this happens? Have you ever wondered why it happens? After all, it doesn’t look or feel that good.
Up until the early 2000’s, the main theory of how fingers and toes wrinkled in water was that you simply were filling up with water. The dead skin (keratin) cells, which are thickest on your hands and feet, was meant to absorb water causing you fingers and toes to swell and thus to wrinkle.
However, there were a few holes in this theory. Firstly, your hands and feet have less volume when wrinkled in the bath. So they’ve actually shunk, not increased with the water. Secondly, researchers observed way back in 1936 that fingers with damaged or severed nerves did not wrinkle, no matter how long they stayed in water. So how could it simply be a matter of your fingers and toes filling up with water?
In 2003, a more robust theory was offered. Vasoconstriction. http://onlinelibrary.wiley.com/doi/10.1002/mus.10323/abstract As your hands and feet have a very high concentration of sweat glands, water passes through the skin of your hands and feet more easily. The water moving into your fingers and toes dilutes the levels of salt in your skin, which is highly regulated by your body. This dilution weakens the tissue cells in your hands and feet which triggers nerves to close down blood vessels. As the blood vessels are now somewhat closed down, the volume of your hands and feet shrinks. The shrinking occurs unevenly due the structure of the tough work areas on your hands and feet. So on a micro level, some areas of your hands and feet will shrink more than others, this unevenness is what causes the wrinkles.
Further research has suggested there is an advantage to water wrinkly skin for us humans. If you think about racing tyres, and you’ll start to understand what I’m talking about. Race cars use slick flat tyres in dry conditions for the best grip, but then change to wet weather tyres with grooves for the best grip in wet, rainy conditions. The grooves help channel water away allowing the flat surface to grip. In 2013, an experiment (http://rsbl.royalsocietypublishing.org/content/9/2/20120999.full) tested this theory via moving wet marbles and fishing sinkers to and from different containers while timing the results. In the experiment, people who wrinkled their hands for 30min in water prior to the test managed to complete the slippery tasks, on average, 12% faster than those with unwrinkled hands. There seemed to be no advantage or disadvantage for moving dry objects with wrinkled hands which might explain why we don’t have wrinkled hands all the time. Outside the experiment, it is suggested that wrinkled hands are less sensitive and damage easier which also could explain why our bodies don’t wrinkle all the time.
It is thought that wrinkled hands and feet might have given our human ancestors an advantage when it came to hunting and gathering in wet environments. Some interesting thoughts for when you are next pruning up.