Dermatologist Laurence Meyer of the University of Utah offers this explanation:
The epidermis, or outer layer of the skin, is made up of cells called keratinocytes, which form a very strong intracellular skeleton made up of a protein called keratin. These cells divide rapidly at the bottom of epidermis, pushing the higher cells upward. After migrating about halfway from the bottom of this layer to the top, the cells undergo a programmed death. The nucleus involutes, leaving alternating layers of the cell membrane, made of lipids, and the inside, made largely of water-loving keratin. The outer layer of the epidermis, called the stratum corneum, is thus composed of these alternating bands.
When hands are soaked in water, the keratin absorbs it and swells. The inside of the fingers, however, does not swell. As a result, there is relatively too much stratum corneum and it wrinkles, just like a gathered skirt. This bunching up occurs on fingers and toes because the epidermis is much thicker on the hands and feet than elsewhere on the body. (The hair and nails, which contain different types of keratin, also absorb some water. This is why the nails get softer after bathing or doing the dishes.)
Soaking in the tub does hydrate the skin, but only briefly. All the added water quickly evaporates, leaving the skin dryer than before. The oils that hold the water in have usually been stripped out by the bath¿especially if soap and hot water are involved. But if oil is added before the skin dries, much of the absorbed water is retained. Thus, applying a bath oil or heavy lotion directly after a bath or shower is a good method of hydrating the skin.
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9 Comments
Add CommentThis is a good explanation. I believe fingers swell as a result of osmosis. The skin is a membrane separating the inside from the outside of the body. Because there is more water on the outside of the body (in the bathtub), there is a tendency for the water to flow inside the body. The skin will allow only so much water, or we would inflate like a balloon every time we got wet. The fingers and toes have tight little attachments holding the skin down, so when the skin swells, these attachments pull the skin downward creating a dimpling effect. There is more bunching in the tips of the fingers because the skin is thicker there. Other areas of skin still swell but it looks smoother. We don't blow up like a huge balloon because there is a waterproof layer of oil on the top of our skin, and because of the nature of our selectively permeable skin.
Reply | Report Abuse | Link to thisWhy should we want to hydrate our skin?
Reply | Report Abuse | Link to thisThis is very interesting; however, it seems to me that this response doesn’t really answer WHY our fingers wrinkle but HOW. As I have been exploring the Net looking for an answer to this question, I have discovered many similar scientific and medical responses. So far, these responses have explained in detail HOW we think our fingers (and toes) wrinkle. Some of these articles seem to approach the question as they attempt to explain what makes our fingers, palms, toes, and feet different than the rest of our skin? It seems the assumption here is that the wrinkling of our fingers merely a side effect of contact with water.
Reply | Report Abuse | Link to thisA similar question “Why do we get goosebumps?” would likely be answered in a completely different way( i.e. http://www.scientificamerican.com/article.cfm?id=why-do-humans-get-goosebu) When we think about goosebumps we think about animals and evolution or stimuli and responses. Why don’t we look into WHY our fingers wrinkle in this way?
Since I cannot find the answer, I would instead like to offer a hypothesis instead… Why do our fingers and toes wrinkle when wet? I think it is simply a matter of traction. Our fingers and toes have adapted to form natural Aquatreds. I think if we were to study the difference in grip/traction on wrinkled vs. unwrinkled skin, we might see that the wrinkled skin offers a greater advantage on wet surfaces than the unwrinkled. This also might explain why we have wrinkle prone skin on just our hands and feet; these are the locations where grip is most important. Try this: Soak one hand in water until wrinkles appear. Next, get your other hand wet. Before wrinkles appear on this hand, compare the traction on different smooth surfaces. What do you think?
--Excessively Curious Computer Scientist
A very intruiging hypothesis. You have a valid point but its my observation that when hands are wet and wrinkly they become softer and easier to cut. If what your saying is true gripping anything remotely sharp (lets say jagged rocks)would cause harm to the animal and prove counter productive for hands to become soft and wrinkly.
Reply | Report Abuse | Link to thisThere is a "famous" criminal case going on now near Cincinnati, OH, where this "pruning of the hands" is one of the key issues. State v. Ryan Widmer. State alleges Ryan killed his new wife by drowning her. Ryan says he was watching a football game, while his wife bathed and he went upstairs and his wife was dead in the tub. EMTs say "no pruning" of hands/feet at the scene was suspicious. Questions include: why does this happen, how long does it take, how long does it take to go back to normal once you're out of the tub, what happens if someone dies before/during the "back to normal" process?
Reply | Report Abuse | Link to thisAs far as I can tell, the court is allowing all types of "medical" people, EMT's etc, to testify about this but it seems to me the physiology of this is not well known and should be subject to some better medical/forensic testimony than EMT's saying what they "usually" see. I was online looking up the answers when I came across this posting, which is different than other postings, including some medical postings, which indicate we don't really know or understand exactly why this happens. I haven't found anything on a timeline though... the coroner is supposed to take the stand soon, so maybe he'll shed some forensic light on this...
This case became "famous" because it's the third trial. First jury convicted him, but that verdict was tossed out when it came to light that jurors had experimented at home to figure out how long it takes a body to dry off once removed from the tub. After that Dateline ran a show on the Widmer case. Second trial resulted in a hung jury. Widmer III is now going on...
You may want to hydrate your skin because it's dry. Dryness on the skin may cause itchiness. This makes the skin uncomfortable.
Reply | Report Abuse | Link to thisThere are two types of skin: thick skin and thick skin. Thick skin consists of four layers starting from the deepest and moving superficial: Stratum Germinativum that consists of basal cells that divide producing more keranitocytes; Stratum Spinosum where the desmosomes that attach these cells together become noticeable as they lose water, and gives this layer a spiny effect; Stratum Granulosum that is left with protein and other substances once the nucleus and organelles die, producing a granular effect; and the top layer the Stratum Corneum that consists of many layers of dead, flat keratinocytes. This layer contains hair follicles and sebaceous follicles that produce sebum that lubricates the skin. It covers approximately 99% of the body.
Reply | Report Abuse | Link to thisThick skin has an extra layer found between the Stratum Granulosum and the Stratum Corneum called the Stratum Lucidum; this is a thick, transparent layer. Thick skin is only found in the palms of the hands and the soles of the feet, and does not contain hair follicles nor sebaceous follicles.
I hypothesize that the Stratum Lucidum restricts or inhibits the absorption of water; and therefore water is only absorbed in the coroneum layer. The expansion of the keratinocyes as they absorb water causes the skin to buckle and bend producing the wrinkling effect of the palms and soles, and fingers and toes.
I was looking at the same explanation that skin wrinkles to give more friction under water to find fuel for the aquatic ape hypothesis. I do agree with 4. j_carrillo, cuts are a lot easier to get. Jury still out then.
Reply | Report Abuse | Link to thisErm - sorry to rain on your parade, but this explanation is completely wrong. In 1937 it was found that finger wrinkling was controlled by the autonomic nervous system. If you damage the nerves running to your hand or foot, you can stop them from wrinkling. Wrinkling is used as a clinical test for autonomic nervous function. If you use lumbar epidural infusion you can effectively turn wrinkling on or off. It is not caused by water absorption.
Reply | Report Abuse | Link to thisThe wrinkles themselves are caused by vasoconstriction of blood vessels in the finger tip pulp (the pad of flesh on the fingertip). This in turn gives rise to reduced finger tip pulp volume. So, rather than your skin getting bigger, it is the other way around, the underlying flesh gets smaller and the skin stays the same size. Although there is some evidence that a small amount of water soaking into the epidermis may be what initiates this effect
This raises the interesting question of why does this happen. Why have a system that actively makes our fingers wrinkle. The latest (Jan 2013) paper shows experimentally that wrinkled fingers have better grip than smooth ones. The idea is that our pre-human ancestors evolved the adaptation to help in wet arboreal environments.
Take a look at the Wikipedia article on wrinkles. It has a pretty good summary and links to original sources. Reference number 6 is about the grip experiment mentioned above and has a brief literature review at the start.
Interestingly, the reason I came to this page is because I was looking for website resources that had the water osmosis explanation of wrinkling - as an example of popular science mythology. Imagine my surprise to find Scientific American promulgating what has been disproven now for nearly 80 years. Shame on your Sci Am.