If you've spent some time in a bathtub, hot tub or swimming pool, you've probably noticed that your fingers are wrinkled, like raisins or prunes. Once you're out of the water, you may notice that your skin loses its wrinkles pretty quickly. The reason skin wrinkles when it's wet has to do with the biology of human skin and how it works to retain moisture and protect the body.
Features
Human skin consists of three layers. The innermost layer is called the subcutaneous layer. The middle layer is the dermis, and the outermost layer is known as the epidermis. The main job of the epidermis is to protect the body from losing water, to protect the other skin layers from injury or disease and to dispose of dead skin cells by flaking or shedding. The epidermis is tightly attached to the dermis just below it.
Function
The epidermis is made of multiple layers. The outermost layer is called the stratum corneum, which is a Latin phrase meaning "horny layer." This layer sheds dead skin cells. It's particularly thick on the fingers and toes. Another layer of the epidermis is responsible for producing sebum, a protein that slows the dead-skin-shedding process and waterproofs the skin.
Process
When you take a bath or soak in a swimming pool or hot tub, some of the waterproofing sebum your skin creates is washed away. This can happen more quickly in the bathtub or shower than when swimming, because when you wash you are scrubbing away the dead skin cells and the sebum layer protecting them. As your skin loses its sebum, it becomes less able to repel water and soaks up some of it. Because the epidermis is tightly connected to the skin layers beneath it, it wrinkles, creating more surface area to accommodate the water you've absorbed without being pulled away from the dermis.
Balance
As soon as you get out of the water, the extra water stored in your epidermis begins to evaporate. As it does, the cells in the epidermis that absorbed the extra water begin to shrink back to their natural size, which is why your skin looks normal again a short time after you're done with your bath or swim. However, because being in the water scrubbed away some of your skin's natural sebum, the skin may be drier than it was before.
Expert Insight
According to Discover magazine, certain types of nerve damage in the fingers and toes prevent the skin from wrinkling in water. Hospitals sometimes check for this nerve damage by putting a patient's hand or foot in a bucket of water and checking to see whether the skin wrinkles. If the nerve damage is repaired, the skin may start wrinkling again.
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