Ask Dr. Universe: Hair growth has its roots in our follicles
Washington State University
Dr. Universe: How does hair grow? – Aidric, 9, Ohio
Dear Aidric,
People grow hair on every part of their bodies except the palms of the hands and soles of the feet. Most human hair is just super fine and hard to see.
That’s what my friend Edward Johnson told me. He teaches classes about the human body in the School of Biological Sciences at Washington State University.
He also told me hair grows from follicles. Those are special organs in the top layer of the skin. Everything you need to grow hair is inside the follicle.
“In the epidermis, which is the outermost layer of the skin, the cells dip inward,” Johnson said. “At the bottom, they form the hair bulb. That’s part of the hair follicle. There are cells there that multiply. They grow upward from the follicle, and as they grow up, the hair gets longer and longer.”
Each hair has a root. That’s the part of a hair that’s inside the follicle.
The hair bulb is at the bottom of the hair root. It’s connected to nerves and blood vessels under the skin. The blood brings nutrients to the cells in the hair bulb. Those cells begin to multiply.
The new cells clump together and get stiffer. They push the hair up. That makes the hair outside the skin longer. A head hair grows about one centimeter – or a little less than half an inch – every month.
But hairs fall out, too. Humans shed between 50 and 100 hairs every single day. You probably see them in your hair brush. Or in a big slimy clump in the bath tub drain.
That happens because hair has a resting phase. At a time set by your genes, a hair separates from the nerve and blood vessel at the bottom of the follicle. Without any nutrients, the cells stop multiplying. The skin slowly pushes the rest of the hair out of the follicle until it sheds.
Eventually the growing phase starts again. The cells get nutrients and begin to multiply. Soon, a brand-new hair starts growing in the follicle.
Head hair has a longer growing phase than other kinds of hair. The hair on your head can get very long. The growing phase is much shorter for other kinds of hair. That’s why your eyelashes and nose hairs don’t grow as long as your head hair.
Johnson told me that hair color happens inside the follicle, too. That’s because of a pigment called melanin. Special cells in the follicle inject two kinds of melanin into new hair cells. Eumelanin makes brown to black shades. Pheomelanin makes yellow to red shades. The amount and type of melanin determines the color of your hair.
There’s sure a lot going inside that tiny organ in your skin. You could say it’s pretty folli-cool.
Sincerely,
Dr. Universe