时差N小时 梅子干皮肤（在线收听）

Prune skin on this Moment of Science At some time, we've all probably taken a long bath or been in the pool for a while, and then notice that parts of the palms of our hands and the bottoms of our feet became wrinkled. This Moment of Science answers two questions about this. Why does it happen? And why doesn't our whole body wrinkle like that?

梅子干皮肤？对，我们这次的内容与皮肤有关。有时候，我们可能在浴池或泳池中的时间较长，然后，会发现手掌和脚底板的皮肤起了褶皱。本次内容将对这一现象做出科学的解释。为什么会发生这种情况？为什么我们的整个身体不会出现褶皱？ The answer lies in the structure of our skin, and that is not the same all over. The outer layer of skin, the epidermis, on our palms and the soles of our feet is thicker than the skin on the rest of our body. When we soak in water, the epidermis all over our body absorb some water and swells. Because the skin on our palms and soles is thicker, it can absorb more water, and therefore, swells more.

答案在于，我们身体各处的皮肤结构并非完全相同。手掌或足底的外层皮肤（真皮）要比身体其它部位的皮肤较厚一点。当浸泡在水中时，外层皮肤会吸收一些水，然后膨胀。因为手掌和足底的皮肤较厚，它吸收的水分更多，因此膨胀得也就越多。

That seems simple enough. But why did ends our fingers and toes wrinkle like black prunes and not the rest of us? Most of our skins absorbs water and swells rather evenly, but there is something different about ends of our toes and fingers -- there is a nail on one side. The ends of the fingers and toes can't swell towards the nails, so the skin bunches up opposite nails on the palm side of our fingers and the sole side of our toes. This bunching up of the skin gives us the wrinkles, prune skin.

道理似乎很简单了。但是，为什么手指和脚趾的末端褶皱得像黑色的梅子干，但其它部位则不会如此呢？原因在于，当皮肤吸收水分时，大部分会均匀地膨胀，但手指和脚趾的末端结构有点特殊：那里生长着指甲（趾甲）。当吸收水分时，手指和脚趾末端的皮肤无法向指甲（趾甲）的方向膨胀，因此，那儿皮肤就会缩成一团。结果，我们看到，指甲（趾甲位置的皮肤会皱起来，看起来就像梅子干一样。