Discussion»Questions»Science and Technology» The hair on your head never stops growing....yet the tiny hair on your body crows only to a certain length and stops...
The hair on your head never stops growing....yet the tiny hair on your body crows only to a certain length and stops...
If you shave the hair on your body ,it will regrow to a a few millimetres and stop....How do hairs on your body know when there are the right length...?
Wait... if the hair on my head never stops growing, then why am I nearly bald?????
Seriously... if I remember my science, it has something to do with resting phases (?). Head hair has a short resting phase (when the follicle stops growing) - 20-30 days (I think), while other hair follicles have a longer rests. Hair on other parts of the body gets broken off easier (due to clothing) than head hair.
Also, there is no such thing as gray hair. Hair is normally semi-transparent. However, each follicle produces pigment which "colors" the hair. Over time, follicles lose this pigment. Due to light refraction, we see "gray" hair.
This post was edited by Shuhak at April 6, 2019 1:11 PM MDT
Its a nice question. I know its weird to say , but if you cut/shave some hairs somewhere on your body, it will make the hairs grows even more after it...
For example, on my butt.... I cut the hairs when its long but it keep growing back. So sometimes its not a win-win situation.
A follicle will produce new cells for a certain period of time depending on where it is located on your body. (The hair follicles on your head are programmed to let hair grow for years at a time.) This period is called the growth phase. Then it will stop for a period of time (the rest phase), and then restart the growth phase again.
When the hair follicle enters the rest phase, the hair shaft breaks, so the existing hair falls out and a new hair takes its place. Therefore, the length of time that the hair is able to spend growing during the growth phase controls the maximum length of the hair.
The cells that make the hairs on your arms are programmed to stop growing every couple of months, so the hair on your arms stays short. The hair follicles on your head, on the other hand, are programmed to let hair grow for years at a time, so the hair can grow very long.
Animals that shed have hair follicles that synchronize their rest phase so that all of the follicles enter the rest phase at once. This way, all of the hair falls out at one time. A dog that sheds will lose its hair in large clumps. Many animals can also switch the coloring agent in the hair follicle on and off -- so in the summer, the hair is pigmented brown with melanin (see How Sunburns and Sun Tans Work to learn about melanin), but in the winter it is not pigmented, leaving the hair white.
(unintended pun, apparently---the arctic hare is white in winter: The Arctic hare is the largest hare in North America. Its fur is grayish-brown in the summer. It has short ears with black tips. In the winter, it has all white fur, except for the black tips on its ears. Its white fur helps camouflage it from predators in the winter. In the northernmost parts of its range, it is always white. https://nhpbs.org/natureworks/arctichare.htm)
Shuhak 