How come your hands get all wrinkled after they’ve been in water?
How come your hands get all wrinkled after they’ve been in water? asks Kelsey Steck, a student in Holtsville, NY.
While nearly everyone gets pruny fingers after a long bath, their exact cause is still a mini scientific controversy.
Part of the explanation involves how skin responds to water. While skin is a good protective covering for our bones and organs, it isn’t waterproof. In fact, skin is nourished and plumped up by water, even absorbing it from the air around us.
The skin’s outer layer, the epidermis, is attached to the thicker layer underneath, called the dermis, but there is some “give” between the two. Hair follicles in the dermis pump out sebum, an oil that protects and lubricates the skin. But the undersides of fingers and toes (as well as palms and soles) don’t have hair, and don’t have as much protective oil.
Meanwhile, the skin on hands and feet is quite thick. Submerge your hands in warm water for awhile, and the oil that protects the skin (and makes it a bit waterproof) washes away. So as you soak in the tub, the keratin protein of the extra-thick epidermis on your hands and feet will soak up 6 to 10 times its own weight in water, like an absorbent paper towel. As the epidermis swells with water, it pulls away from the dermis and folds up into ridges and furrows. (On palms and soles, the epidermis is so tightly anchored to the dermis that it can’t crimp up.)
Interestingly, researchers have found that people with Parkinson’s disease, diabetes, and other diseases that damage the nervous system or blood vessels often show reduced or absent finger wrinkling.
How come? In a study published in 2006, researchers in Taiwan compared ordinary fingers to reattached fingers, in which nerves had been severed in the past. In normal fingers, immersion in water reduced blood flow by more than 27 percent, and the fingers pruned up nicely. But when the reattached fingers soaked in water, blood flow actually increased by nearly 23 percent, and the fingers remained smooth and wrinkle-free. This suggests, the researchers say, that wrinkling is due more to the actions of nerves signaling the constriction of blood vessels, rather than to a property of the skin itself.
So what’s the whole story behind wrinkled digits? One explanation: Water kicks off the wrinkling process by seeping in and altering the balance of electrolytes (liker sodium and potassium) in the skin. This changes the functioning of nerve fibers (if they are intact), which in turn trigger a narrowing of the blood vessels leading to fingers. As the vessels deflate, the negative pressure tugs the plumped-up epidermis down into wrinkles. (Sufferers of Raynaud’s phenomenon, in which blood flow to the fingers is sharply reduced in cold temperatures, also report getting mildly pruny fingers, even when their hands are dry.)
Meanwhile, doctors can test the health of nerves in the hand and fingers after an injury by submerging the fingers in water. If the tips get wrinkly, it’s a good sign.
