How do hairs on your arm know when to stop growing?
In: Biology
Simple answer: they fall out. Every hair on your body has an average lifetime that depends on where it is on your body. Hair falls out when it reaches its natural length, and a new hair starts to grow in its place. Arm hair falls out way more often than head hair. Head hair can grow for something like 7 years before it falls out. This happens all the time, so if you never got a haircut or a shave, your head hair and body hair would max out wherever the natural length is for each body part. Since we don’t want to look like cave men and women, we usually trim up the places where it tends to grow too long.
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