system
Given the following post, respond as if you're commenting on Reddit:
human
How does body hair "measure" its own size and when to stop growing?

Body hair has a set length (correct me if i am wrong but afaik it is set in the genes?), but how does a single hair "know" how long it currently is or when to stop growing?
gpt
>Body hair has a set length

Close.  Each hair has a set **time** for it to grow.  After spending that set time growing, it will fall out and a new hair will start growing from the follicle.

So, for instance, if you cut a hair, it won't grow to its full length.  Rather, it will keep growing for its set time limit.  But with lots of hair all grouped together, and with each hair on a separate "timer" (that is, they're not synchronized), you get the overall appearance of hair regrowing to a set length.