Wrinkly fingers
I remember one time when my boy was just a wee baby, he looked at his hands whilst in the bath and mildly started freaking out. Yes, his fingers were all wrinkly, and this was his first experience with it.
We’ve all noticed it at some time or other. Go for a swim, wrinkly hands. Have a shower, wrinkly hands. Running a marathon in the rain, wrinkly hands. (Actually, only the first two for me!)
So why do we get wrinkly fingers when we get wet? Well, it’s simple really. Vasoconstriction - a constricting of the veins - in our hands and feet.
Yes, but why does that occur?
Ah, that’s where it gets a bit tricky, and is actually still up for debate.
A lot of people used to think wrinkly fingers was the result of osmosis. This is when water moves into the outer layers of body tissue due to an imbalance in salt concentration. This water absorption would cause the fingers to swell. The swollen outer layer of skin, still tightly attached to the layers beneath, would then wrinkle due to the increased surface area. However, measurements have shown a decrease in finger volume when wrinkled, not an increase, as would be the case if swelling was the cause. And even more damning than this, it has been shown that if you cut the sympathetic nerve fibres (the nerves that respond to your “fight or flight” response) to a person’s fingers, they will no longer wrinkle in water.
So it seems to be our sympathetic nervous system that is responsible for wrinkly fingers and toes. Water diffusing into our porous skin is thought to cause the reaction by the sympathetic nervous system initiates vasoconstriction.
The question now is how the sympathetic nervous system gets stimulated by water, and that is where the debate lies. There are two main theories:
1) Electrolyte imbalances in the epidermis (the outermost layers of cells of skin).
2) An overproduction of sweat by your sweat glands.
Theory 1: Numerous studies have used finger wrinkling as a test for how well sympathetic nerves are functioning in limbs, and they generally cite electrolyte imbalances as the most likely cause of an increased fight or flight response to the extremities. When water diffuses into the many sweat ducts of hands and feet, the increased water volume creates an abnormal balance of electrolytes such as sodium, potassium, calcium, magnesium, chloride, and bicarbonate. This electrolytic imbalance causes the sympathetic nervous system to induce vasoconstriction.
Theory 2: Sweat glands at rest produce sweat at certain pressures. That droplet is then evaporated depending on the environment. In water, evaporation is absent, resulting in a sweat droplet that continuously grows in size. The total pressure of the atmosphere and water, at a depth of 10 cm, is 767 mmHg. But sweat glands produce a pressure of 1260 mmHg. This higher pressure pushing on sweat droplets cause a free-flow of sweat from the body. In response to the excessive loss of sweat the sympathetic nervous system triggers a reduction of blood flow to the hand, causing the vasoconstriction and eventual wrinkling of the skin.
You can choose which side you want to take. Number two doesn’t sit right with me, so I’m going with number one.
Anyway, what you may have noticed is that the vasoconstriction of the fingers and toes occurs whether the water is cool or warm. Take a dip in a running (cold water) creek or wash the dishes in hot water, the result is the same. The fact that it is independent of water temperature suggests an evolutionary benefit to wrinkling fingers and toes.
In 2011, evolutionary neurobiologist Mark Changizi first proposed the idea that wrinkling of the skin gives us a gripping advantage in wet conditions. He suggested the wrinkles that form on our fingers exhibit consistent patterns that allow water to sluice away, indicating that their role is to improve traction, like the tread on a tire. The hypothesis was confirmed early in 2013 by neurobiologists at Newcastle University in the UK. They found that along with the advantages in wet environments, wrinkled fingers gave no disadvantage in dry conditions, suggesting a superiority in one situation whilst not diminishing our protection in others. Surely, that is the work of evolution.