Finger-Grapes?

Today I had a long bath. It took me a while to realize, but I saw that all of my fingers were wrinkly. It is the same as I had observed numerous times before in the swimming pool (and even at times in heavy rains). But why does it happen?

Why Do Our Fingers Become Wrinkled When Wet?

Our body is a wonder-house. Every part of it has hidden and surprising elements that we never really realize if we don’t notice things properly. For example, our skin (the outer layer) in covered with a special oil like substance called sebum. Sebum keeps our skin moist and lubricates the skin which provides protective function. This is the reason water doesn’t soak into our hands when we wash it.

Staying a long time in water can lead to washing off of sebum. This leads to water penetrating into the skin. But as we all have read/experienced, if water goes into a piece of wood (or something else like our skin), it swells the wood rather than wrinkling it. Then what is actually happening?

The response is an internal response as opposed to a physical one. Nerves cause the blood vessels to constrict on our fingertips, reducing the amount of blood flow to the fingertips. Just as a dried grape turns into a raisin, the loss of blood flow turns our fingers into the wrinkled raisin like appendages we see. But why?

Scientists (Changizi et al.) studied this phenomenon and came up with a possible explanation. The wrinkled fingertips are an evolutionary favoured strategy to increase grip inside of water. This may have been a valuable effect that may have helped our ancestors in hunting fish or grabbing stones and objects while crossing streams or rivers. As for us, we can gracefully grab the side rails after a long session of calm swimming in the pool.