system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the hair on my arms, legs, eyebrows etc. stop growing at a certain length but the hair on my head/face will continue to grow until it is cut?

Just a thought I had while mowing the lawn.
gpt
Hair growth is coded for a specific time period, then stops/dies/sheds.

The hair on arms, legs etc. has a shorter growth time period than head/facial hair.  Your head/facial hair will stop at after a certain time period (which will determine its final length).