Is it that they don’t know or the “threshold” is so long that we don’t get to see it very often?
In: Biology
There is an actual reason that I don’t see here but I’m late to the party!
As people have said previously, hairs grow from follicles, inside your skin. Some do indeed grow forever, like your head hair (if you’re lucky.) They age and fall out due to a lot of different reasons including what you eat and how healthy you are.
Hairs that don’t grow forever get their length determined in the genes of the cells in the follicle. But how do they sense their length?
Longer hairs wiggle! Cells in the follicle can sense mechanical stress as well as grow hairs.
Say we talk about a hair in your leg, just above your ankle. As it grows, moving in life causes it to wiggle a certain amount. Just a little bit at first. Then as it gets longer it’s more likely to catch air currents, rub on things, and get pulled more. The follicle knows how much wiggle is associated with how long the hair is. If it wiggles just a little it’ll hang on to the hair. If it wiggles to much it stops growing the hair and may even let it go after a certain amount of time.
Incidentally you can see this work, especially around the ankle when people wear socks for a long time. The constant movement of the sock on the ankle can sometimes make hair growth finer or even stop it entirely. This happens in athletes. Now on the other side of the spectrum, people that wear socks for to long but don’t move, say when they’re in a coma, usually grow very long ankle hairs because there is no wiggle.
Latest Answers