Protein layer called keratin makes wet fingers wrinkle

You wanted to know

Why do our fingers and toes get wrinkly in the bathtub? A student in Cindy Bumbales’ first-grade class at Lincoln Prairie Elementary School in Crystal Lake wanted to know.

Scientists don’t exactly know why soaked fingers and toes become pruney. But there are a few ideas why skin puckers when submerged.

“It’s because the outside layer of the skin, the epidermis, has a protein layer — keratin — that allows water to be absorbed as it swells,” said Dr. Lori Walsh of Glenview Pediatrics and the Ann & Robert H. Lurie Children’s Hospital of Chicago.

“It’s a fun way to say you’ve been in the bathtub.”

Water washes away protective oils on the surface of your skin. Keratin absorbs water. Skin below the top surface doesn’t take on as much water, so the top layer buckles, forming wrinkles. This process is called osmosis.

After a long soak in the tub or a watery day at the pool or beach, how is it that just your fingers and toes are pruney? Why don’t your arms and legs look like the wrinkly skin of a Shar-Pei puppy?

It turns out that the skin on your hands and feet have the most keratin, a protein that toughens up the skin, so they are the most likely body parts to reveal your watery whereabouts.

Scientists discovered that people who have had fingers restitched into place have less of a chance to become pruney after washing dishes or bathing. They suspect that this may be the case because blood flow might also trigger the wrinkle effect.

More studies could show that reduced blood flow might pull the plug on the wrinkly skin, making it smooth instead.

Some scientists think pruney fingers are an ancient response from the times when our cavemen ancestors might have had to keep their hands below the water’s surface for long periods to catch a fish.

Studies show that wrinkly fingers have better gripping power. Researchers concluded that the wrinkles act like treads on a tire to improve grip in watery conditions. What researchers haven’t yet studied is whether wrinkly toes provide a better grip on the soap in the bathtub.