By the way, doctor: Why does skin wrinkle after being underwater?

Q. Why do our hands and feet wrinkle up when immersed in water? Your article about moisturizers said they work by trapping water in the skin, so why don't we wrinkle up after applying moisturizer?

A. The top layer of our skin, the stratum corneum, is like a sponge that absorbs water when it's immersed. And when it's filled with water, it expands and gets softer and more pliable. And, as you've noted, only the under sides of the hands and the feet prune up, especially the fingertips and the toes. That's because the stratum corneum is thick there.