Why do the skin wrinkle when immersed in water

“The most widely believed reason for wrinkling of skin on fingers when immersed in water is based on absorption of water by the outer protective layer of skin called the stratum corneumThis causes the skin to expand on account of absorption of water, thus resulting in a larger surface area. To accommodate for this larger surface area the outer skin is forced to wrinkle.”

       When our fingers are immersed in water for an extended period of time, the skin on the fingers tend to wrinkle, this condition is commonly referred to as pruney fingers or water aging.  This phenomenon is usually explained on the basis of absorption of water by skin.
       The outer layer of skin is composed of three layers – the epidermis layer which is the outermost layer, dermis or the middle layer and subcutaneous or innermost layer. The epidermis layer is in turn made of four separate layers – stratum corneum which is the outer most layer,  granular layer, squamous cell layer and basal cell layer.
       The outermost protective layer of skin is called stratum corneum. The primary function of this layer is to protect the underlying tissues from damage and the outer covering of this layer consists of dead keratin cells and protein and fat. And stratum corneum has a tendency to absorb water. As water is absorbed by the layer, the surface area of the skin increases and the skin is forced to wrinkle. The wrinkling of skin is found to be maximum in areas where the layer of keratin is maximum. This also the reason why skin on hands and feet tends to wrinkle the most, since it has the thickest keratin layer compared to other parts of the body.
       The time taken for wrinkling of skin is also found to depend on the composition of water, in seawater the rate of wrinkling is found to be low while in fresh water the rate of wrinkling is found to be high. 
       However in 1935 Lewis and Pickering found that wrinkling does not occur in patients having nerve damage in fingers, thus showing that wrinkling is an involuntary action of the body controlled by the autonomic nervous system, which is also responsible for involuntary function of the body such as respiration.
       Wrinkling is thought of as an evolutionary function which provides better grip in wet conditions.

References


[1] http://en.wikipedia.org/wiki/Wrinkle#Water-immersion_wrinkling
[2] http://www.scientificamerican.com/article/why-do-our-fingers-and-toes-wrinkle-during-a-bath/
[3] http://www.loc.gov/rr/scitech/mysteries/wrinkles.html
[4] http://www.scientificamerican.com/article/why-do-our-fingers-and-toes-wrinkle-during-a-bath/