[JumpCrisscross]

> why eyebrows stop growing and NOBODY ever thinks about it

If you clip your eyebrows, will they grow back to their original length? Or is there a process that generates an eyebrow hair and then stops after a pre-determined length of time (with periodic shedding)?

[estimator7292]

Every hair grows to a maximal length before stopping or falling out. It varies wildly based on genetics, location on the body, and body chemistry.

Animals evolved specialized hairs for different uses. Protection, warmth, display, your armpit hairs wick sweat and keeps your skin from rubbing. It's beneficial to have a system that keeps the specialized hairs in their optimal(ish) configuration and to replace hairs as they become worn and damaged.