Why Do My Fingers Get Wrinkly in the Tub?
Micaiah (left), age 3 1/2:
"That's when you take a bath for a long, long time. It feels funny. Your fingers look like raisins because they get squishy from the water. I don't like raisins."
What We Learned
During long baths our padded fingers and toes soak up water like a sponge, making them swell. This happens because the top layer of skin (the stratum corneum) on fingers and toes is more porous than the layers of skin underneath, and thus better at absorbing water, says Jeffrey Newman, M.D., of the dermatology department at the University of California, Davis.
Here's the wrinkle: The reason our fingers and toes don't swell up like water balloons but instead shrivel like raisins has to do with the way the layers of skin are joined to one another.
When the top layer absorbs water, it swells, becoming larger than the lower layers to which it's attached. The skin doesn't detach from our fingers, so the only thing it can do is wrinkle up to accommodate the increase in surface area.
Once we step out of the tub, the water from our skin evaporates into the atmosphere, like perspiration, and our skin quickly returns to its normal form.
Explain It to Your Kids
Take a dry pop-up sponge, hold it flat on its narrow side, and trace its outline on a piece of paper. Then throw the dry sponge into the tub or a bowl of water and watch it expand. Tell your child that the sponge is like our fingers and toes, good at absorbing water.
After the sponge swells up, wring it out a bit and have your child try to fit it back in the outline on the paper. Just like the skin on our fingers and toes, the only way the sponge will fit in that shape is if it squishes up, creating wrinkles — like a giant raisin.