[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

The average growing cycle of hair is around 6 to 7 years when you don’t cut it and it doesn’t break. You’ll reach, what scientists call, terminal length. It’s the longest a hair can grow. Most people never get to that as nobody grows out their hair for 7 years without cutting it.

And there are various other factors influencing your hair growth.