Why Does Hair Only Grow to a Certain Length?

Jack B. asks:  Why does a person’s hair only grow a certain length and then stop, but then when you cut it, it will grow back to its maximum length?

Now You KnowI very briefly mentioned this in an article about two years ago that you might also be interested in (There is No Difference Between Fur and Hair), but I’ll go into more detail here.  Hair length is completely controlled by the length of the anagen phase of your hair follicle.  How long this period lasts is generally determined mostly by genetics, but can also be affected by hormones, and even extreme stress.  More specifically, there is a chemical signal that ultimately controls the exact growth cycle.

Following the anagen phase is the catagen phase.  It isn’t yet known what triggers the catagen phase, but once it is triggered, the outer part of the root ends up being cut off from its nutrient supply (blood), as well as the cells that produce new hair, thus your hair stops growing. This phase lasts about three weeks.

Next up comes the telogen phase where the follicle is in a resting state and your hair is now a “club hair”, completely dead down to the root.  During this stage, these hairs are relatively easy to pull out (as can happen while brushing/combing/washing your hair), but if they manage to last long enough, they’ll eventually be pushed out by a new hair as the cycle begins again.

Obviously hairs on your arms or legs have a very different anagen period than hairs on your head, thus why your leg hair doesn’t grow two feet long without trimming.  Further, different people, thanks mostly to their genetics, have differing lengths of the anagen period for a given body part compared to other people.  For the hair on your head, the average length of the anagen phase is about 2-7 years.  For your arms, legs, eyebrows, etc., this phase usually lasts just 30-45 days.  However, in extreme cases which are quite rare, some people have anagen periods for their heads as small as most people’s anagen phases for their arms and legs.  For these people, their hair never naturally grows more than a few inches long, presumably saving them a significant amount of money over their lifetime on barber visits. 😉  The opposite is also true, with people whose anagen phase can last decades for their scalp hair.  Both of these extremes are very rare though.

At any given time about 85%-90% of your hair is in the anagen phase, 1-2% is in the catagen phase, and 10-14% is in the telogen phase.  However, extreme stress can trigger the anagen phase to stop prematurely and hair can rapidly progress to the telogen phase, even as much as 70% of the hair on your body.  When this happens, the majority of your hair that should still be growing can fall out all at once.

Under normal circumstances, though, you can get a rough estimate of how long your anagen phase is based on how long your hair grows naturally without cutting on a given area.  First, assuming your hair isn’t already as long as it can get, measure your hair length, then exactly a month later measure it again and note the difference.  Now you have your growth rate (usually about 1 cm every 28 days or 1 inch every 71 days).  So if, without cutting, the hair on your head eventually grows 16 inches long max, then your anagen phase lasts: (inches*period per inch).  So using the average of 1 inch every 71 days, (16 inches * 71 days/inch) = approximately 1136 days or 3.11 years.

Now to specifically answer the second part of your question “…but then when you cut it, it will grow back to its maximum length”, this is just because when the cycle restarts, new hair comes in that can grow to the maximum length, eventually replacing the old hair that will be shorter than it could have been because you cut it.

As you might have now guessed from the fact that hair growth is completely controlled by what’s going on under the surface, within your hair follicles, and that genetics and hormones are the primary things determining hair growth length, which are in no way affected by shaving, shaving does not in any way alter your hair growth rate nor does it alter the color of the hair.  You can read more about this here: Shaving Does Not Make Your Hair Grow Back Thicker or Faster

Another hair fact article you might be interested in, which happens to be one of my favorite articles on this site, is this one:  What Causes Red Hair

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  • Some people still wonder why a hair grows back when cut because they get the idea hair was not growing until they shaved.

  • great my hair will always look fugly

  • A 4 inch circle at the top of my head produces hair that will literally not grow beyond 2-5 inches.This happened after I had children. I used to have great long hair!! Now I practically have a mullet.

    • Hi Melissa, despite cutting won’t make your hair grow back faster or longer than the length it’s programmed to grow (because other factors address such length, like Christee said, which make the anagen last for a longer hair length), yet if it’s split ends that hinder your growth, cutting helps it.

    • i also have this problem too melissa! and down the centre at the back so i have a gap at the back , :(

      • Have you verified they aren’t just split ends? To do this, have your ends slightly cut and see if the hair will keep growing after this. Have someone verify the ends with a lens.

  • For those of you who want longer hair, I have heard that MSM will prolong the anagen phase. 😉

    I can’t prove anything but my hair is now longer than it has ever been in my life (I’m 39). It used to grow just past my shoulders and now it is down to the middle of my back and hasn’t shown any signs of stopping.

    Oh, and don’t worry if you have a sulfa allergy…not the same thing.

    • What is MSM?!? My hair just stopped growing the last 4 months and of course, it happens to be while I’m trying to grow out my pixie cut!! I used to have 38 inches of hair within 4 years and now it won’t budge! I am freaking out! I feel like crying. I treat it good and a healthy fitness junkie so now, I’m worried! Please help! :(

      • Hi, sorry for that. Have you seen a tricologist? What length are you stuck at, if it’s bob length, you might check for split ends yourself or have a friend of yours do it for you if your hair isn’t long enough to take it in front of your eyes behind a lens :). Your hair might be in that case splitting away from the tip at the rate at which it grows. If it’s not the case or the growth doesn’t “restore” (it’s actually an illusion that it’s not growing because of tip erosion) after you cut the splits, your hair might really have stopped growing past that length.
        If you want to test whether or not it stopped growing or only past a certain length, dye a thin lock of hair a visible red up to it’s root or close to it. Yeah you may or may not be comfortable with it, depending on your style in this case, single out a lock so that it’s covered by other layers of hair and not in the layers you most frequently expose with your hairstyles. If you are comfortable with such look, you might as well dye a thicker lock :).
        Now cut this lock visibly shorter than the rest of your hair, measure its length and take note of it.
        If the red highlighted lock starts to grow back while the rest of your hair is not growing (besides of course a few shorter hair that have been growing from scratch as the long/old ones have been recently shed) past that same length, it might means that your terminal length have shortened for some reasons, but short or shortened hair is still growing as long as the length is not reached.
        In any case you are visiting a tricologist, but you could also bring this test and its outcomes.

  • Why does one body hair (on my wrist or leg) grow about 4 or 5 times as long as the ones next to it?

    • Some hair is more androgenized, I think. I have also a black long terminal on my upper arm, while most of it is little more than peach fuzz, sometimes I shave it, paying attention not to shave anything else (it would look funny to see completely hairless zones among light fuzz ). It also happens, when a process of hair thickening is in course and we are witnessing the first hair which is going to replace peach fuzz with terminal hair in schedule, that happened all over when my beard was starting to develop, more and more terminal hairs among fuzz.

  • So the people who have hair down to the back of their knees just have a long anagen phase? So if I stopped cutting my hair for the rest of my life it would only grow to however long it is set to grow at maximum length?

    • Yeah, basically they do, some people’s hair grow indefinitely, even past their own height, if their growth phase even has an end, they don’t find it in their whole life :D. Keep in mind, though that not all of their hair grows this long, only a part of it, mostly their side hair, in fact the very end length of their hair close to the tip are always sparser and see through, most of their hair don’t grow that long, that’s why they still shed hair regardless of a part of it growing “in(de)finitely” :)
      Yours might not grow this long, but you also likely have a part of it which will grow much longer than a part of it.

  • How come my hair only grows on one side of my head? Ever since I’ve had a baby my right side doesn’t grow. I used to have longer hair and now i have it above my shoulders because I have to keep it the same length. I always sleep on my right side, and I heard that is a huge factor, but is there anything to do to help this out besides switching how I sleep?

  • Please help. My hair has always been my pride and fucking joy. I figured since it is pretty damn healthy, it could deal with some bleach damage. And I figured the master stylist who did all the color-corrections would know how much would be too much. I was wrong, and now I want to burst into tears every time I look at my hair or touch it. I just don’t know what to do. my hair has also NEVER been shorter than this and it breaks and falls out. What should i do to regrow hair?

  • My growth cycle used to be about ten years. My hair was below my butt when I was in my teens. I kept my hair shoulder length. My friends warned me it wouldn’t grow back like it did in my teens because our hormones change after kids. I’m 35 and have only been trimming it since I was 28. It’s growing faster than it used to. So is the hair on my shins. I thought I’d have less hair after my kids. But the hair on my head and shins is much better/worse. It’s down to my waist again and it’s thicker than I remember.

    I’m getting curious just how long the hair on my head will grow, but annoyed with hairy shins. Every two days I need to shave them. In my teens, once a week was fine. How do I make hair grow more slowly?

  • You could try topical spironolactone creams, but I’m not sure, consult your doctor about it ;).
    They are hormonal changing and should revert back after pregnancy, though. Are your hair growing longer too?

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