This is Why Your Fingers Get Pruney in the Bathtub, And No, It's Not Osmosis

It happens just about every time you shower: you're in there for a while, scrub-a-dub-dubbing (or if you're me, pondering existential questions about life), and after a decent amount of time, your fingertips get all prune-y. You may never have bothered to figure out why that happens, but I'm going to tell you anyway because scientists finally have an answer for why your fingers get wrinkly in water. As an aside, I would like to know if anybody else calls the way your fingers look, "pruney," or if it's just my family.

Until today, I have actually given myself a headache trying to figure out how this phenomenon works. I figured it was by osmosis, but if I remember anything from eighth grade science, doesn't movement of particles through semipermeable membranes move from areas of high concentration to low concentration? And there's no way my fingers would have a higher concentration of water than water, so...what was going on? Update: I just looked it up and osmosis moves water from low concentration to high concentration; apologies to all my middle school science teachers.

Anyway, it turns out all of that research (which took me approximately .37 seconds to complete) was in vain because your fingers do not turn pruney because of osmosis. It's actually caused by a response in your nervous system. I repeat: not osmosis. Here's a one-sentence explanation:

OK, so it's a natural response that your body automatically triggers, like blinking when somebody pretends to hit you across the face, I guess? But why?

Scientists think pruney fingers might date back to evolution. We might have developed this function so we could grip things better when our hands are wet. In 2013, researchers set out to test this hypothesis and found that people with wrinkly fingertips picked up wet objects better than people with smooth fingertips. Aha!

Watch the whole video below to get probably a better explanation about what's happening, and also to answer the following questions:

Does having prune-y fingers help you pick up dry objects better?

Why aren't our fingers wrinkly-looking all the time?

If it's a water thing, why do my fingers look just as raisin-like after taking off a band-aid?

SciShow on YouTube

I lied about that last question, that definitely did not appear in the video, but I am still very curious to know!

Images: Sarah (on the mend) / Flickr; SciShow / Youtube