[Nagisa pointedly ignores the comment about nobody wanting to watch Jataro work and instead squats down on the other side of the sand worm, looking pointedly at Jataro's hands as he starts smoothing the sand. Who cares if nobody else wants to? He does and he's going to, so there.]

One would have to stay out in the sun for a very, very long time for that to happen. Actually, if it's only a matter of hours, the opposite is true. Your skin will swell up if you get a really bad sunburn. But...eventually, yes: too much sunlight can make your skin wrinkle. [He folds his arms on top of his knees so that he can rest his head on them as he continues to watch from his squatting position. He's still clearly trying to avoid getting sand on anything other than his feet.]

Your skin wrinkles in water for a completely different reason, though. People have been studying the effect for years trying to figure out why it happens. All the evidence seems to point to it being an involuntary nervous system reaction. It causes the blood vessels in your hands and feet to constrict, which in turn causes your skin to wrinkle and fold.

[Because you wanted the actual explanation, right Jataro?]