Does hair stop growing?

November 7, 2009 9:44 AM

Hair growth question: some people say that their hair will only grow until a certain length. Is this a myth? How would the follicle know when to stop growing?

Some of my friends claim that their hair will grow until a certain length and then just stop. At first, I thought that this was just a broken-hair issue (that older, longer hair would "break" with brushing), but then I met people with perfectly healthy, strong hair that claim the same thing. Is this just a myth? How would the hair follicle know when to stop growing? Are they just impatient and get haircuts before they allow their hair to grow longer? Is it just an impression that hair grows faster when it's shorter?
My hair doesn't stop growing so it's hard for me to understand.
Thanks!

posted by Neekee to health & fitness (14 comments total)

I can't answer this, but I can add that I've known a number of people who didn't cut their hair for long periods, including myself, and it only ever got to a certain length. Mine was middle of back to butt length, and seemed to be the case for most people I knew.
I have no idea what the mechanism of it remaining that length is, aside from potentially it matching up with the point at which that hair falls out or something. Given how much of my hair (which was thick) fell out every day it could just be that.
posted by opsin at 9:48 AM on November 7

This sounds like an old wives tale of the "if you shave it it grows back thicker" sort. I think you're right in thinking that shorter hair just appears to grow faster, and there are probably other similar illusions at play.

Basically I am nigh on 100% sure nobody's hair knows when to stop growing.
posted by Nomiconic at 9:49 AM on November 7

Hair must have some sort of mechanism to stop growing, otherwise we'd all have a lot more body hair. I don't think one of my arm hairs have ever grown longer than an inch. Head hair is different but may have similar growth parameters. Perhaps the cells in the hair follicle only live for a certain amount of time- but that's a total guess on my part.
posted by emd3737 at 9:55 AM on November 7 [3 favorites]

Do you trim your eyebrows? Arm hair?
posted by Sys Rq at 9:56 AM on November 7 [1 favorite]

Hair doesn't stop growing and then just hang around; each individual hair falls out after a certain amount of time, so the maximum length equates to the maximum lifespan of a given strand of hair.

See here and here.
posted by ook at 9:58 AM on November 7 [3 favorites]

After some further research, I found this, which says basically that follicles allow hair to grow for a certain amount of time and then just let it fall out, and the follicles on one's head have an extremely long growing period. So, my bad! Your friend's hair and your own and anyone's can apparently can only grow to a certain length.
posted by Nomiconic at 10:00 AM on November 7

You are viewing the issue backwards.

The follicles do not "know" when to stop growing, they grow at a certain rate and for a certain tine and then the follicle goes dormant at which time the hair is no longer retained and falls out.

The length of the growth cycle and the rate of growth puts an absolute upper bound on the length of the hair from the follicles as does the strength of the hair itself (and this also changes over time). These to traits vary from person to person.

See also:

http://en.wikipedia.org/wiki/Hair_follicle#Hair-follicle_cycling
posted by rr at 10:05 AM on November 7

This is pretty easy to answer with some googling. I'm pretty sure there was a Straight Dope about it. It grows for a fixed amount of time, then starts a new strand. So there is a real limit to how long your hair will grow. There is no evidence that shaving or waxing has any long term change in hair once it grows back.
posted by chairface at 10:17 AM on November 7

Hair does stop growing. In the active hair growing anagen phase the follicle continues to produce fibre for three to six years. Then, the hair enters a rest phase called catagen for up to three weeks after which the hair falls out in the telogen phase. Normally, at any point in time 90% of your hair is in anagen and the other 10% are in telogen. It's a matter of genes, sex, age and, overall health that determines how much you have and, how long it can get.

keratin.org has a easy to understand section on hair biology including hair growth rates and, maximum hair length.
posted by squeak at 10:30 AM on November 7 [1 favorite]

Another aspect of this that can be seen in action is that the hairs that are growing vs. the dormant ones are pretty randomly spaced. If you get a buzz cut, it won't grow back like a chia pet, but rather uneven. At about two weeks, you'll see that some hairs are growing and other's have not left the station, as it were.
posted by qwip at 11:43 AM on November 7

Hair falls out, on a replacement schedule, if you will. If your hair grows fast, and the replacement schedule is slow, you'll be able to grow it longer. If your hair grows slowly, and the replacement schedule is pretty fast, you won't be able to grow it very long.

Shaving or cutting doesn't affect fair growth; plucking/waxing will eventually kill the hair follicle.

Bonus factoid - your hair grows slower in the side of your head you sleep on.
posted by theora55 at 12:21 PM on November 7

Think about your eyebrows and eyelashes. There has to be a reason why they don't grow over your eyes, right?
posted by zinfandel at 8:39 PM on November 7

Can't speak for head hair ... but comments upstream about it falling out are NOT NECESSARILY TRUE for body hair ... or, at least I have a single data point which demonstrates otherwise.

I have a lone single dark and thick 12mm hair between my right thumb and fore finger. It has been there for years. Sometimes I have cut it down close to skin level, and it has regrown to 12mm. There it stops. It has not fallen out in my memory (and I would notice) ... but it has been cut short at least 3 times.

This is not a friend's cousin's brother's 12mm hair ... it is mine ... on a hand I am typing with right now.
posted by jannw at 4:20 AM on November 8

My hair doesn't stop growing so it's hard for me to understand.

How long is your pubic hair?
posted by HiroProtagonist at 8:40 PM on November 8