[ELI5] Why do some hairs continue to grow and others don’t?

Question

For example, head hair seems to grow forever if I don’t cut it, but my arms doesn’t, there’s like a *limit* of growing

In: 0

Answer 1

There isn’t a limit on growing. The hairs on your arms continuously grow. The very tip of your arm hair eventually reaches a point that wear and tear causes it to break off or it may fall out at the root and start over again. Since this eventually happens to all hair after a certain point depending on how long that hair has been growing, it seems like there’s a limit on the length when really it’s the age of the hair imposing that limit.

You may notice that a particularly thick hair, like one growing out of a mole ends up being much longer than the others. This is because it’s thickness allows it to withstand wear and tear longer than the rest of your body hair.