Ask Dr. Universe – Fingernails

What are fingernails made of? -Amy, 8, Seattle, WA

Dear Amy,

My claws can come in quite handy when I need to scratch my ears or climb trees. I bet you’ve found that your own fingernails can be useful tools, too. Perhaps you’ve used them to pick up a penny or peel an orange.

It turns out that while my claws and your fingernails look a little different, they are actually made out of the same thing: keratin.

That’s what I discovered when I went to visit my friend Professor Lisa Carloye, who teaches biology here at Washington State University.

As you may know, your body is made up of living cells, which make a wide variety of proteins. In fact, about 20 percent of your body is actually made up of proteins—proteins like keratin, which help cells do different jobs.

Sometimes this means building fingernails and toenails. Other times it might mean an animal will grow claws. Claws can then be used for defense, to catch prey, or climb. Keratin can also help some animals grow hooves. Horses, for example, walk on their toenails. It gives their feet a little extra support on rocky ground.

“Claws and hooves and fingernails are all basically the same thing,” Carloye said. “They are adaptations of the same process. Keratin itself is what gives fingernails their rigidity, their strength, and flexibility.”

Oftentimes, fingernails will start growing even before you are born. The process all begins underneath your skin.

If you take a look at someone’s fingernails, you may notice a small crescent moon-shape at the base. It’s called the lunula, the Latin word for little moon. Sometimes it’s easiest to see it on the thumb. The lunula is actually part of the nail called the matrix.

The matrix creates new cells, which help form new layers of keratin. Once fingernails start growing, they’ll keep on growing about two inches each year. The longest nails ever on a pair of hands were measured at more than 28 feet total.

As the fingernails grow and poke up out of your skin, the cells actually die. That’s why it doesn’t hurt to trim your nails at the top. As you may have noticed, it doesn’t hurt to get your hair cut either.

“The other place we find keratin is in hair,” Carloye said. We also find it in fur, feathers, and the top layer of human skin, she adds.

Some scientists can use fingernail clippings, or other kinds of samples that contain keratin, to learn more about what animals eat. Other scientists are curious about how nails grow at different rates and why. Perhaps one of the most devoted nail scientists was William Bean, who observed and tracked his own nail growth for more than twenty years.

We are still looking for more answers to why nails, claws, and hooves grow exactly the way they do. But now you know that keratin makes up our nails and helps them grow—slowly, but surely.

Dr. Universe

Got a science question? E-mail Dr. Wendy Sue Universe at Ask Dr. Universe is a science-education project from Washington State University.