Why Do Only Certain Parts Of My Skin Wrinkle In Water?

Summer is the season of sunshine, lemonade, and swimming pools. As I got out of the swimming pool today, something hit me: Why do the skin around my fingers and toes become wrinkly?

The skin is the largest organ of the human body with a surface area equal to a medium sized dining table (~20 square feet). The skin on the palm and toes are thicker than other parts since they are intended to minimize the damage that occur in day to day interactions such as walking and gripping items.

The extra thickness of skin in these parts are caused by the protein keratin, which is nourished in the deeper layers of the skin and forms a coating of dead cells on top of the epidermis (the outermost) layer. Hands and feet have the thickest layer of keratin cells, hence the skin here is thicker than anywhere else on the body. These dead cells are constantly shed and replaced.

When skin comes into contact with water for at least 5 minutes, the dead keratin cells soak up water like a sponge, causing them to swell. The living cells underneath wrinkle to compensate for the sudden increase in the surface area of the swelling keratin dead cells. Thus, they appear wrinkly.

Reference:

https://www.nature.com/news/science-gets-a-grip-on-wrinkly-fingers-1.12175

http://www.bbc.com/future/story/20160607-why-your-skin-goes-wrinkly-in-the-bath

http://www.loc.gov/rr/scitech/mysteries/wrinkles.html

http://health.howstuffworks.com/skin-care/information/anatomy/hands-and-feet-different-skin.htm