Getting A Handle On Why Fingers Wrinkle

Why do your fingers get pruney after a long water bath? Only a handful of researchers (ever) have looked into the finger-wrinkling experience. Reporting in the journal Biology Letters, researchers make the case for finger wrinkles as treads — wet wrinkled fingers seem to grip better than wet smooth ones.

IRA FLATOW, HOST:

Up next, Flora Lichtman is here with our Video Pick of the Week. Hi, Flora.

FLORA LICHTMAN, BYLINE: Hi, Ira.

FLATOW: Now, we've got some digital research on this one. The other - the classic definition of digits, which...

LICHTMAN: The analog digital, your fingers.

FLATOW: Your fingers. That's what it means in Latin or something, right?

LICHTMAN: Well, they are your digits. I think digital typically refers to what we were just talking about. But yes, this week's video investigates the hard science topic of why your fingers and toes get wrinkly after a long soak.

FLATOW: That is something that we've all observed and we've all wondered, and we all think we know why for some reason.

LICHTMAN: So why do you think? What's the common prevailing sentiment?

FLATOW: My prevailing sentiment is that we have oils on our skin, right, oils on our skin that keep them smooth. And when you get soapy water, we know soap takes the oils out and so they're not smooth anymore. And for some mysterious scientific reason, they wrinkle up.

(LAUGHTER)

LICHTMAN: Well, that is...

FLATOW: Have we found it?

LICHTMAN: We apparently have not solved it. I thought that it was having to do with osmosis, that water entered your skin. And I'm not alone in thinking this. A quick survey of the Internet suggests that other people thought this, too. But it is not osmosis at all that is doing this. And it doesn't seem to be your theory, either, I'm sorry to say.

FLATOW: Now what? Just a thought.

LICHTMAN: No, no, exactly. So - but people have looked into this. There's, you know, a handful ever in history to have looked into this. And one is Einar Wilder Smith. He's a neurologist, and he found that what is causing the wrinkling, it's regulated, actually, by your nervous system.

So here's what happens: You dip your hand in a bath of warm water, and your nervous system, for some reason - and just exactly why is not clear, he said. But it tells the blood vessels in your hand to constrict, and they get smaller. And he thinks that what is happening is that when those blood vessels get smaller, the volume in your fingertip goes down. You get a pressure differential. And basically, your skin just, like, sucks in, like a balloon deflating. But imagine that there is some structure there, so you have - you get the wrinkles.

FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR, talking with Flora Lichtman, our multimedia editor about our Video Pick of the Week. And in our Video Pick, you actually spoke - videoed him, right?

LICHTMAN: Yeah. I spoke with him via Skype. He's in Singapore. But I went everywhere. I just had to know. I, like, went down the rabbit hole of wrinkly fingers this week. So that was the first...

FLATOW: You got into the research.

LICHTMAN: Yeah, big time. So the first was a mechanism, right?

FLATOW: Right.

LICHTMAN: But then the question is: If this is controlled by our nervous system, if this is not just chemical thing, why is it happening? And it only happens on your fingers and your toes. So this guy, Mark Changizi, who's a neuroscientist, suggested last year - 2011, so a couple of years ago - that the reason we have these wrinkles is to grab a hold of things when we're in a wet condition, that it's easier to grab a hold when you have the wrinkly skin. And, in fact, the wrinkles are like little channels, sort of like rain treads on your tires that take the water and channel it out so that you have a better grip. And the way that he made this argument, which is ingenious, is that he looked at mountains which have the same topography, he argues, as your fingertip.

FLATOW: Hmm. Sure.

LICHTMAN: And if you look at the way the water channels off of a mountain, the pattern is just like the wrinkle pattern on your finger. So he actually said that when he's flying now, he just - whenever he sees a mountain, he just sees pruney fingers everywhere.

(LAUGHTER)

FLATOW: And they are the same pattern in everybody, right?

LICHTMAN: Yes. There's sort of standardized pattern that looks like these mountain channels. So this week, there's more. There's more, everybody. If you could...

FLATOW: Yes, there's more?

LICHTMAN: ...if you can imagine. This week, Tom Smulders took up this hypothesis and tested it. So you basically made people pick up wet objects and move them from bin to bin. And he found that people with wrinkly fingers versus people with unwrinkled fingers, those people with wrinkled fingers actually moved the objects more quickly than the unwrinkled finger.

FLATOW: The unwrinkled finger. But, as you say, but it all starts in our nervous system, which I found to be the most fascinating part of the (unintelligible).

LICHTMAN: That is, for me, also kind of the biggest ah-ha here.

FLATOW: Yeah. You know, it's not like your skin reacting by itself, like you say, through osmosis or something. But your brain - something in your brain is saying, I'm in water now. I better do this.

LICHTMAN: Yeah. And this raises some interesting questions - like, for instance, if you submerge your whole body in water, except for your hand, will your hand wrinkle? You could try this at home. Let us know.

FLATOW: Wow.

LICHTMAN: I haven't done this experiment.

FLATOW: Put that out...

LICHTMAN: If you have a bathtub, you could try this experiment.

FLATOW: Maybe if you're a scuba diver and you're always in the water, maybe you've noticed this already about being...

LICHTMAN: That's true. You might know. Also, do other animals get wrinkly fingers? Mark Changizi looked into this via Google image search, and he found the faintest glimmer of evidence that these Japanese macaques, which spend a lot of time in hot springs, seem to get wrinkly fingers. So that would - he thinks that aids his hypothesis about the gripping.

FLATOW: I think we need more research.

LICHTMAN: Yeah.

(LAUGHTER)

FLATOW: Let's seek a research budget.

LICHTMAN: I think everyone would agree. But it's interesting that you say that, because, you know, Mark Changizi, who just had his theory, his hypothesis sort of validated this week, seems to have some mixed feelings about this whole field.

(SOUNDBITE OF INTERVIEW)

MARK CHANGIZI: I mean, I was joking. I was saying, oh, God. I hope that I don't get remembered for this, because I have a lot of things I've done. And I can imagine my tombstone: Here lies Changizi, and here's this tombstone that has been carved into the shape of a wrinkled thumb.

(LAUGHTER)

LICHTMAN: I understand.

FLATOW: I did all this - yeah, but it's a fascinating...

(LAUGHTER)

LICHTMAN: (unintelligible)

FLATOW: That's right. I spent my whole life, and all I got was this tombstone. (unintelligible)

LICHTMAN: But, no, but it is - it's really - it's this kind of amazing thing, where it's something that happens to all of us, and yet there's been almost no research to try to figure out why or how.

FLATOW: Yeah. Well, there's no money to be made on it.

(LAUGHTER)

LICHTMAN: That is exactly (unintelligible).

(LAUGHTER)

FLATOW: I'm sure that's why...

LICHTMAN: It's, like, how do you think you get this funded if you don't?

(LAUGHTER)

FLATOW: Well, maybe our listeners - it's Video Pick of the Week. It's up there on our website. You can see the experiment that's done and the explanations and wonderful graphics that Flora's put together. And maybe you can then tweet us back and see - maybe you can do the experiment with - you're holding one hand above the water?

LICHTMAN: Yeah, one hand above the water. The rest of you submerged. Does that hand wrinkle?

FLATOW: Does - yes. Does one hand wrinkle, and would not one hand wrinkle?

LICHTMAN: Right.

FLATOW: Because the body's telling your hands to wrinkle, does it know which hands in the water?

LICHTMAN: Yeah. That's right.

FLATOW: Ooh, I like that. Thank you, Flora. Flora, wow.

LICHTMAN: It wasn't my idea. Thank you, Mark Changizi.

(LAUGHTER)

FLATOW: So, Flora Lichtman, our multimedia editor, our Video Pick of the Week and it's up there on our website at sciencefriday.com - up there on YouTube, also.

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