Thursday, December 26, 2013

Hair and Thair ~ Is There a Doctor in the House?

This may sound silly.  I often ask questions others don't seem to think about.  For instance, if a dog has black fur it's called a "black dog."  Why isn't a person has black hair called a "black person?"

That's just an aside.

I think too much about hair.  It's one of the big differences between the genders.  A woman trying to pass as male might want to add sideburns or facial hair and lament that her arm hair is thin.  A man trying to pass as a woman will work hard to remove or bleach body hair and shave facial hair as close as possible.

Let's consider arm hair.  (Most body hair works the same way, for this thought exercise.)  It grows to, say, an inch long, and then stops.  Just let it sit there and it just... sits there.

I know hair has a lifetime and it will eventually fall out and be replaced, but it's not a very short lifetime.  It's weeks or months, not days.

Yet if you shave it off, it will grow back pretty much immediately.

Shaving is not particularly intrusive.  It's not like epilating or tweezing or using chemicals to remove the hair or otherwise irritate the follicles.  It's simply cutting off the dead part above the skin.  But if you shave it will grow back quickly and stop at the same length as before.

Why does it do that?  How does it know that it's been shorn and needs to grow back?

Is there anyone who understands the biology involved and can explain this to me?


  1. You sound as mad as me Meg. It reminds me of the old joke: "A thermos flask keeps cold things cold & keeps hot things hot. How does it know?"

  2. I think that you're just overestimating the cycle length of your hair growth.

    The hair has no knowledge of the fact that it has been cut.

    There are 3 phases of hair follicle activity ~ growing, resting and dormant. At any given time, some follicles are in each of the three.

    A hair will grow in a follicle, until the follicle decides to rest. At that point, the hair that has grown will remain attached. Hence, the length that the hair grows to will be a function of the rate and duration of growth, which is a combination of genetics and environment (nutrition, temperature, etc).

    Once the follicle decides to stop resting, it will shed the hair then either go back to growing phase and produce a new hair, or go dormant.

    After you shave or chemically burn it off level with the skin, the hairs that are already resting will shed while those that are growing will grow out. Over time, the hair will grow back to the same length and thicken back up to how it was before. The hair that was cut part way through growing will only end up the length that it was going to grow to minus what you chopped off.

    Waxing or epilation will do precisely the same thing eventually, but because you've removed more of the length of the hair, it takes longer to even get back to the skin surface let alone growing to normal length.

    Incidentally, the reason why waxing and epilation gives a smoother, rounded tip and less pigment is that that's how the tip of a new hair grows when the old hair is ripped from a follicle while actively growing. The tip is hemispherical and the shaft begins at a smaller diameter with less pigmentation. Allow it to grow for long enough and it will taper back to its full diameter and regain its full pigmentation.

    By contrast, a shaved hair is cut into a chisel shape because the hair bends over before the blade cuts it through. It also has its full diameter and pigmentation.

    That's why when I epilate my facial hair, I have no beard shadow, but anybody who shaves will have beard shadow no matter how closely they shave...

    Since I'm drivelling on and most people have stopped reading, I'll finish by mentioning that laser and IPL hair removal only works on follicles that are actively growing, so you have to do touch-up treatments for years to get the follicles that decide to come out of hibernation.

  3. Yep, and why does some grow quicker than others, i.e. chest hair sees to grow faster than leg hair.

  4. Alice,
    Thank you for your fine explanation of hair and the way it grows. I liked your explanation about why there is beard shadow no matter how close the shave is as opposed to eliminating it when you epilate. I suppose epilation may be a good idea for many t-girls before they go out.
    I am intrigued by the constant ads for the "No-No" device. How does that stop hair growth. Do you know if it actually works or is just a heavy duty promotional campaign.

  5. I just noticed Pat's question. I don't know the nono device specifically, but there a number of DIY laser, IPL and RF (radio wave) devices out there, and I don't think that any of them have the same power level as a comparable commercial device, so I have no idea whether they work just as well, not as well or not at all. I suspect the latter in most if not all cases.


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