Re: Why do our fingers and toes wrinkled in both bath water and ocean water?

Dear Yu,

Your question is very intriguing. All explanations I was able to find about finger wrinkling suggests that the wrinkles occur because of osmosis, such as at the New Scientist magazine. Osmosis is the term given to the process of water traveling through a semi- impermeable membrane from the side with few solutes to the side with many solutes. In this case the membrane is the cell's lipid bilayer membrane, which is impermeable to many solutes, such as sea water salts.

I can not remember a time that my fingers wrinkled while being in sea water. But being a firm believer in the power of the scientific method, I decided to do an experiment.

I prepared two bowls of water. One contained only warm water, and one contained warm water saturated with table salt. I placed one of my hands in each bowl. After about five minutes the hand placed in plain water was very wrinkly. The hand in the salt water seemed normal. I kept the hand in the salt water soaking for a full hour, but still no wrinkling. In fact, my fingers felt unusually smooth. Science requires repeatability, and so I convinced two of my friends to do the same experiment. (They'll do anything for Science!) The outcome was the same: Wrinkled fingers in the salt-free water, smooth fingers in the salt- saturated water.

So why did your fingers wrinkle when you were in sea water? I can't be certain, but I have a pretty good guess. Your average run-of-the-mill sea water has an osmolarity of around 2000mOs. The human body maintains its fluids at 300 mOs. If your fingers were wrinkling in sea water, that sea water must have somehow been diluted down to an osmolarity of less than 300mOs. This occurs most commonly close to where a river empties into the ocean. The mixture of salty ocean water, and relatively unsalty river water is called brackish water.

The ecology of brackish water systems is fascinating because the osmolarity of the water is constantly changing, presenting a great challenge to the vegetation, animals, and microorganisms in the area. I had the pleasure of working with an expert on brackish water organisms, Dr. Robert Denno at the University of Maryland. Visit his web site and, if interested, read some of the journal articles listed there.

Next time you go to the ocean and see your fingers wrinkle, look around for a fresh water source near by. If it's a river or marsh, take the opportunity to examine the rugged wildlife living in the brackish water!

Thank you for your question,

John