Pruney fingers, water aging, or water-immersion wrinkling occurs after fingers have prolonged exposure to water. But how does the wrinkling work? An early theory was that the skin cells absorb water and expand, forcing the skin to wrinkle. However, those with damaged nerves, leading to the fingers, occasionally do not experience these wrinkly fingers. So what is actually going on?
The theory that pruney fingers are strictly due to water absorption was disproven in 1935, in a study of patients with palsy of the median nerve (performed by Lewis and Pickering). It was noticed that areas of skin which were connected to a damaged median nerve no longer wrinkled after immersion in water. If water absorption is part of the cause for water aging, it only plays one part in the process.
Recent research (Einar P.V. Wilder-Smith, Adeline Chow (2003). “Water-immersion wrinkling is due to vasoconstriction”. Muscle & Nerve) leads to the narrowing of blood vessels as the cause. Water is absorbed into sweat ducts first and alters the balance of electrolytes in the skin. That imbalance causes an instability in the neurons connected to the blood vessels, causing them to fire rapidly. Rapid firing of neurons then cause the blood vessels to constrict, decreasing the fluid (and thus tension) in the fingers and wrinkling the skin.
Because of the direct connection to the nervous system, water-immersion wrinkling is now used as a simple test to search for damaged nerves. A hand is immersed in water for 30 minutes to see if the fingers wrinkle. If they wrinkle, the nerves are functioning. If they do not nerve damage is a possibility (but not guaranteed as not everyone’s fingers wrinkle).