How do hairs on your arm know when to stop growing?
In: Biology
Hair of all types is created by a follicle under the skin that grows it and pushes it upwards. Each follicle can make multiple strands, and each strand has 3 phases of life, and as it ages through these stages it grows less and less as the follicle focuses on a younger hair. Once it reaches the final phase, which for arm hair can last about 100 days, it doesn’t really grow at all, and then naturally falls out to be replaced by a new hair at phase one again. This process is repeated throughout your life, though each type of hair in each part of your body has different lengths on each of it’s phases. Human hair tends to fall out semi-randomly, which allows us to have quite a lot of variation in our hair length, unlike the fur of many other mammals which often has a very reliable life-cycle based, and is why they have totally uniform hair lengths.
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