Why does hair grow?
For grown-ups: the science
Hair grows because new cells keep forming at the root, deep inside your scalp.
Hair grows because cells in the hair root, called the hair matrix, keep dividing and making new cells. As new cells get pushed upward, they change into hard cells full of a protein called keratin. The visible hair shaft outside the scalp is made of cells that are already dead, so it doesn't grow on its own.
What about...?
Ask your child's own question
Transcript
Look at your hair growing longer and longer. Why does it keep growing?
Deep at the root of each hair, tiny cells are hard at work. They keep making more and more new cells.'
The new cells get pushed up higher and higher. Along the way, they turn into strong, hard hair.'
Once hair pokes out of your head, its cells stop multiplying. But since new cells keep forming at the root, your hair keeps growing longer.'
Hair grows because new cells keep forming at the root, again and again.