[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

Actually, hairs don’t stop growing. But some hairs are “programmed” to fall out after a while. It’s why you don’t have 6″ eyelashes! Of course, they get replaced by new hairs that grow in.