Why do the palms of your hands get all wrinkly when you stay in water for a long time, but the back of your hands and most of your body don't?

-- Tess Phillippi, 10, Grants Pass, Oregon

Wrinkled hands are sometimes called prune palms. Some parents try to get their kids to take a break from the swimming pool by telling them their whole body will shrivel up if they don't come out. That could happen, said Roselyn E. Epps, dermatologist (skin doctor) at Children's Hospital in Washington. But it could happen only if the kid stayed in the pool or bathtub for days or weeks.

The palms, fingers and the bottom of feet do wrinkle pretty quickly, sometimes in less than an hour. Epps says doctors don't know for sure why this happens, but here's the best explanation:

Nice, fresh living skin is waterproof. But the outer layer of skin is not nice and fresh. It's dead skin. (Nothing to worry about. It's a really thin layer.) The cells, millions of them, that make up dead skin contain a protein called keratin. Keratin tends to soaks up water. So the outer layer of your hands and feet, loaded with keratin, fills up like a paper towel in a puddle.

Since the living skin under the dead skin is waterproof, the water collecting in the dead layer has no place to go. The water is kind of trapped. That makes the outer layer swell up in little patches. This swelling makes the wrinkles.

But why only on the hands and feet? Because the skin is thicker there and takes in much more water. Thin-skinned parts of your body won't wrinkle the same way.

And thank goodness for that. It's one thing to have prune palms and another to have a prune face.

-- Fred Barbash

Staying in the water too long can have consequences.