I found this online. Good question, with a good answer! I learned something!
Richard Sontheimer, head of the University of Iowa College of Medicine's dermatology department, replies: Our skin has a protective top layer, called the stratum corneum, made of protein and fats that absorb water. A primary function of the stratum corneum is to protect the underlying tissue from environmental injury. In areas that experience high mechanical use and friction-such as the palms, fingers, soles, and toes-the stratum corneum has evolved to be thickest and hence most protective. As a result, these areas of the skin can absorb the most water. They also have less room for expansion and therefore tend to wrinkle most when they get wet. The type of water one soaks in influences how quickly the skin on hands and feet wrinkles. Seawater, which has a high mineral content, tends to keep water from penetrating into the skin. The relative absence of minerals in household bathing water, on the other hand, tends to exaggerate water penetration into the skin. So you will wrinkle more slowly if you are swimming in the Caribbean than if you are showering at home. Wrinkling from prolonged water exposure is a process distinct from the generalized wrinkling caused by aging. The latter is due predominantly to loss of elastic tissue in the underlying dermal layer of the skin, two layers beneath the outermost stratum corneum.
<img src="http://rfcop.50megs.com/images/aggiesox.gif">Go Saux!!! Thanx Aggie