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Everyday Mysteries: Fun Science Facts from the Library of Congress

Why do fingers and toes wrinkle in the bathtub?

The outermost layer of the skin swells when it absorbs water. It is tightly attached to the skin underneath, so it compensates for the increased area by wrinkling.

There are various theories of why fingers and toes wrinkle in water. Most biologists suggest that the tough outer layer of skin made up of dead keratin cells is responsible. Keratin is a protein found in hair, nails, and the outermost layer of our skin.

Our skin is made up of three layers:

The subcutaneous tissue is the deepest layer. It contains fats and connective tissue along with large blood vessels and nerves.
The dermis is the middle layer. It contains the blood vessels, nerves, hair roots, and sweat glands.
The epidermis is the topmost layer. It helps to prevent evaporation of water from the body and to protect the internal layers from harm.

The epidermis is made up of four layers:

the stratum corneum
granular layer
squamous cell layer
and basal cell layer

The stratum corneum is the outer layer of our skin - the part that we can see and feel. This is the layer with the dead keratin cells.

While a person is in the pool or a bathtub for a long time, the dead keratin cells absorb water. This absorption causes the surface area of the skin to swell, but the outer layer is tightly attached to the living tissue. So, to compensate for the increased surface area, our skin wrinkles.

So why does this happen to hands and feet and not to other parts of the body? Because the hands and feet have the thickest layer of dead keratin cells. Our hands and feet are subjected to a lot of wear and tear. Imagine if the palm of our hands had skin as thin as that on our backs. No fun playing basketball with skin that thin!

For more fascinating facts about the skin see the following Web sites and further reading sections.

Related Web Sites

About the Skin - This Web site, from the British Association of Dermatology, provides all types of information about the skin, such as the importance of skin and its role as a barrier, as well as information about skin cancer and other diseases.
Anatomy of the Skin - This Dermatology Health Guide, from The University of Maryland Medicine, contains interesting skin facts and information on skin diseases and conditions.
What causes wrinkled fingers? - A discussion about what causes wrinkled fingers from the Biolab listserv. The Biolab listserv is an email list for discussion of issues and information related to teaching college biology.
The Whole Story on Skin - "Created by The Nemours Foundation's Center for Children's Health Media, Kids Health provides families with accurate, up-to-date, and jargon-free health information they can use." The section on skin provides interesting skin facts, an illustration of the epidermis, additional articles about the skin, and related web resources.
The World of Skin Care: an on-line reference by Dr. John Gray, provided by the P&G Skin Care Research Center - This reference from Procter and Gamble provides information about the structure, function, and care of skin as well as information about skin problems and aging. The information is presented in a book format with a table of contents and index.