Why and how do some hairs “know” when to stop growing (e.g. eyebrows, arms, eyelashes) while others (e.g. scalp, beard) doesn’t seem to?

Question

Is it that they don’t know or the “threshold” is so long that we don’t get to see it very often?

In: Biology

Answer 1

Eyebrows know when to stop growing in size?

Tell that to mine, I have a few that just grow and grow and grow. I have to cut them so they don’t get too long

Answer 2

I think you’ll find your eyebrows are lulling you into a false sense of security, just wait, you’ll wake up one morning and they will be out of control.