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

Does the amount of time that scalp hairs will grow vary from person to person? Do people actually have a maximum length that their hair can grow to? I wonder about this because ever since puberty, I’ve never been successful at growing my hair past shoulder length. I wonder if this is because of something inherent in my hair.