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Question Why do fingers and toes wrinkle in the bathtub?

Answer

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. However, new research is investigating the role of digital vasoconstriction (narrowing of blood vessels) of water immersion wrinkling of the skin.

Soaking in the hot springs. Big Bend National Park, 2004. National Park Service, NP Gallery.
Soaking in the hot springs. Big Bend National Park, 2004. National Park Service, NP Gallery.

There are various theories as to  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
Cartoon showing man and dog in tub, with the man scrubbing himself with brush. Wilhelm Busch, 1865. Prints & Photographs Division, Library of Congress.

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!

Morning bath. Whakarewarewa, New Zealand, 1890-1910. Prints & Photographs Division, Library of Congress.

Scientists continue to look for the exact mechanisms of why our fingers and toes wrinkle when immersed in water (Wilder-Smith et al, Hsieh et al). One theory gaining recognition is the role of digital vasoconstriction (narrowing of blood vessels). When hands are immersed in water it seems that the nerve fibers are triggered to “shrink” and glomus bodies (body temperature regulators in the skin) in the hand lose volume, which then pulls the skin structures downwards to produce wrinkling. Studies on patients with loss of nerve function in their hands due to a disorder or replantation of amputated fingers exhibit no or slight wrinkling in the fingers when immersed in water (Hsieh et al). As the nerve functions return, so did the wrinkling.

The coastal defence guns: One of the crew takes a bath under the shadow of the gun, between 1940-1942. Prints & Photographs Division, Library of Congress.

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

Published: 11/19/2019. Author: Science Reference Section, Library of Congress

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