Body hair mystery (to me)

[SueSheeMee]

Could I Google this? Absolutely. But I don't want to.

How does your body hair, other than your head hair, know to stop growing when it reaches a certain length? You can shave it or trim it and it grows back, but when it reaches that certain point, it doesn't get any longer. What's the science?

Saturday nights don't get much more exciting than this.

Unfortunately not for me!

I once read that we have a third set but they don’t come down! No idea if its true

It's so weird really. My pubic hair would coat my knees if I allowed it free rein, which is ridiculous because, whatever sexual-attractant purposes it may exist for, having it knee-length does the exact opposite.

Do you mean there is one little person in charge of all the hair follicles? Because that’s a lot of work. Or one little person for each follicle? Because that’s just silly.

Hair has three growth phases and these are programmed differently for body and scalp hair (and for different races, and different life/,hormone phases). Scalp hair stays long in the growth phase (anagen) 2-7 yrs approx depending on a range of factors while body hair stays in this phase for weeks to months, so "matures" quickly, stops growing (catagen phase when follicle separates from blood supply) then enters the telogen phase when new hair basically pushes old hair no longer being fed.
Racially Asian hair stays longest in feeding and growing phases so grows faster and longest. second is caucasian then African.. Another fun fact, the EDAR mutation which is extremely common among Japanese, Korean and Chinese people and other east Asians means they have bigger follicles hence straightest and thickest hair but also less body hair, more sweat glands overall and affects the shape of their incisor teeth.
oh and did you know? Chemo can cause hair colour changes. A friend's hair turned from white blonde (she us norwegian) to chocolate brown. Both gorgeous but it was a shock to her (and all of us incl docs)
The body, its genes and programming are amazing
Glad you asked this @SueSheeMee

That’s fascinating @NautilusLionfish, thank you. I have known several people whose hair has regrown curly (having previously been straight) following chemo.

It has a different purpose to the hair on your head. Nose hair has the job of stopping dust and crap going up your nose. Eye brow hair is to stop sweat/rain dripping in your eyes. Pubic hair is to stop shit going into your vag and reduce friction(yes that is its purpose!). Underarm hair is to help you dissipate sweat and also reduce friction. Head hair is to keep heat in (and swish off flies thinking pony tail😂). All hair is made in follicles that are specialised depending on where they are on your body. You started by being just an egg and a sperm which fused together to become a cell. The cell went through mitosis (splitting/multiplying), as they multiply the genetics switches on or off the genes so they become either skin cells, liver cells, heart cells, hair follicle cells, each having a specific function. Hence different hair follicles create different hair for different functions depending on what they are needed for and so they have different growth cycles. Let’s face it, you probably wouldn’t want the type of hair on your arms growing on your head too short to style!.
it’s been decades since I did genetics so my memory might be a little fuzzy so I think that’s correct.

Not human mystery related BUT animal fur…. How does their body know to produce each individual hair strand with carefully aligned changes in colour to make a pattern???? Eg a tabby cat!

It doesn’t, it just grows for a certain period of time, stops, and then falls out. People’s hair grows at different speeds, which is why some people can achieve longer hair than others.

I would love this to happen, it would mean less dental costs

This is fascinating thank you! Hair also seems to react to stress. My sister's hair went from very curly to almost straight after our dad died. I've also heard of people going grey/white overnight due to significant stress, but not sure if that's a myth (it happened to Miss Wilson in the Chalet School books when they had to flee to Switzerland over the Alps to escape the Nazis!)

Curly/straight hair is often hormonal. I know someone who went curly at puberty, straight in pregnancy, then curly again, then straight at menopause.
My aunt had white hair which came back brown after chemo.

Billy Connolly had a hysterically funny stand-up routine about this, pondering how we'd all have to plait our pubes and stuff them down our trouser legs if they didn't know to stop growing

Apart from those bloody chin hairs , I’m sure they have an itinerary all of their own ,

I believe my DM once said that when my DGF died unexpectedly and relatively young, my DGM put her hand to her head and where she had touched went white or grey while the rest of her hair remained it’s normal colour, brown I think.
DM has died but I must ask my older sisters if they heard this.
My hair since I’ve been a teen has only grown to shoulder length and then falls out, although I have plenty of it.
My own question is why do moles sprout long dark hairs?!
PS I’m also a Chalet School fan 😂

It isn't true! Have you never seen one of your dental X-rays? There's no extra set lurking in your jawbones.
On a baby's or young child's X-rays, the adult set of teeth can clearly be seen behind the baby teeth. There's no third set.

It doesn't know it's been cut and go back into the growing phase! If it was no longer in the growing phase it was about to fall out.

My hair mystery is how can I wake up, look in the mirror at my hairless face, go about my day and then return to the mirror that evening only to find a single half inch hair has appeared on my chin!?

Is this for the Guiness Book of Records or does this happen to other people!?

I have always wondered this OP. I wondered if the follicle can sense the weight of the hair, and therefore knows whether it should grow or stop.

For those saying it’s just about growth phases, I’m sure my armpit hair, if left alone will stop growing, but the moment I shave it all starts growing again. I don’t think it ever falls out either

When I was pregnant I got increased leg hair growth with one pregnancy and decreased with the other. One was a boy and one was a girl. I can't remember which way round it was but that was the thing I noticed as I used to epilate at the time and barely had any regrowth with one pregnancy.

Haha! That reminds me of science class in y7. The teacher had us ask questions about the body/sex on bits of paper anonymously then she'd read it out and give the answer.
One kid put 'how does your pubic hair know when to stop growing?' I wish I could remember what teacher said!

I’ve googled it. Some people still have the buds (or remnants of ) for a third set to grow which is a throwback to millions of years ago when it’s thought humans had the ability to grow a third set

@AndresyFiorella, I inherited a grey ‘badger streak’ right at the front of my hair. My mother and her mother both had it. My grandmother died at 55 and still had dark hair overall, just the grey streak at the front. My Mum lived a little longer (65) and was completely grey by then, but her first bit of grey was the badger streak. Mine appeared- not quite overnight, but rather suddenly- when my mum and dad died very close together, so yes, I do believe shock or stress can cause rapid greying.

Sorry not read the whole thread, but essentially cells die because they’re told to die by other cells, this is called apoptosis, it keeps the equilibrium (cancer cells for example don’t die because they’re told to apoptosis and they don’t). Hair cells have a cycle, and once their cycle is reached that’s when they’re told die. It’s the same with all hair, so some people can grow their head hair really long, others can’t, everyone / hair has its length / time to die. It’s why we get hairs falling out too, they’ve been told to die and they do.
It’s a bit simplified, there are different phases in the hair follicle/ cell
Growth cycle but that kind of explains the main bits

Trouble comes when that new length happens to be an inch long.

Obviously improved by my mother blithely announcing that she, of course, never grew hairs on her legs and she was naturally completely smooth. Which was weird when she used to get me to deal with the ingrowing ones that reached 3 inches...