So hair grows by pulling itself upward? Perfect. I’m just going to stand under a ceiling fan and wait for my hair to pull itself back onto my bald spots. Science has finally given me a plan.
This points to a potential answer to a long standing question I've had about why some hairs stop growing at certain lengths. If the force is being generated by cellular migration then control over when to stop growing can be mediated by a signal that tells the cells to stop migrating, and that could be based on time or vibration amplitude or something else that correlates with hair length. For hair that grows continually you just ... never turn off cell migration.
I don't believe any hair on the human body truly grows continuously. Even head hair has a lifespan of ~7 years and whatever you can grow in that time is the max. I was a big metalhead in high school and grew my hair out. Indeed, after about 7-8 years it stopped getting longer, right at about waist level, and was stuck there until I finally got sick of it and cut it off.
> why eyebrows stop growing and NOBODY ever thinks about it
If you clip your eyebrows, will they grow back to their original length? Or is there a process that generates an eyebrow hair and then stops after a pre-determined length of time (with periodic shedding)?
Every hair grows to a maximal length before stopping or falling out. It varies wildly based on genetics, location on the body, and body chemistry.
Animals evolved specialized hairs for different uses. Protection, warmth, display, your armpit hairs wick sweat and keeps your skin from rubbing. It's beneficial to have a system that keeps the specialized hairs in their optimal(ish) configuration and to replace hairs as they become worn and damaged.
Tissot, N., Genty, G., Santoprete, R. et al. Mapping cell dynamics in human ex vivo hair follicles suggests pulling mechanism of hair growth. Nat Commun 16, 10267 (2025). https://doi.org/10.1038/s41467-025-65143-x
Presumably it's produced at the same rate but destroyed by drying out and cracking as it gets longer and has less access to oil, so it slows down and may find an equilibrium where it stays the same length.
Sure. If your hair is breaking off at the same rate it’s growing it’ll be a stable length. I have no idea if that happens though. It seems farfetched that hair would actually be splitting that’s aggressively unless it’s visibly very unhealthy.
If you take proper care of it (which includes trimming split ends so that the cracks don't propagate) then sure, but I've previously neglected my hair to the point where my split ends had split ends. I'll absolutely cop to "visibly unhealthy" but there does come a point where the ends start to fall apart and break off easily.
As someone with thinning hair, it's horrible how little study/research is being performed to understand how hair grows and treat hair loss. Most of the products on the market today were discovered by accident and have serious side effects. This condition impacts millions++ of people, yet everyone from physicians to pharmaceutical companies is fine with the status quo of "here, this may work for you" effectively woo medicine.
You aren't the only person with opinions on it though. Reminds me of the infamous HN thread where a (woman) poster mentioned offhand she and her husband were saving up for transplant for the sake of the survival of their marriage!
> Most of the products on the market today were discovered by accident and have serious side effects.
Topical minoxidil / finasteride has roughly zero side effects (due to the limited systemic exposure) and has something like a 90% efficacy rate. With 90%+ efficacy it's not a case of "this might work for you" it's "this will almost certainly work for you." It's cheap and it works.
Even oral 1mg finasteride has basically the same side effect profile after 1 year as placebo, side effects always* stop whether you stop taking it or continue taking it. And as an added bonus it significantly reduces your risk of low-grade prostate cancer (30% ish) while not increasing your risk of high-grade prostate cancer. Many of the side effects reported are in people taking 5mg doses for prostate hypertrophy, and the incidence of side-effects is dose dependent. Studies show that sexual side effects are primarily nocebo, if participants were told to expect them the rate was 3X higher than placebo, if they weren't told, they were about the same.
* the category of persistent side-effects has been defined primarily for data collection purposes, there's very little evidence for persistent side effects at all let alone a high incidence thereof. Many of the side effects people claim are related are things that would otherwise happen to you at the age you start to lose your hair regardless. It's good to collect more data though.
> As someone with thinning hair, it's horrible how little study/research is being performed to understand how hair grows and treat hair loss.
Given the size of the market I'd say there's a ton of research being done. It's just a tough nut to crack. There's some good data on PP405, for example.
The fact that we're only now uncovering fundamental mechanics like "hair is pulled, not pushed" kind of highlights how under-invested this area has been
As someone with a race in my head between white hairs and a receding hairline, hair loss does afflict millions of people, but it has no medical impact on people's life, beyond increasing the need to wear a hat when outside in the Sun for long. Is it that surprising that medical professionals would spend their time on other afflictions instead?
A social concern where the path of least resistance toward resolution is probably effective medical advancements. For example, studies show bald men face greater challenges in both straight and gay dating in every country where it's researched (so it's not cultural context dependent).
Probably easier to figure out the follicular science than change universal attraction preferences.
It’s not really a big deal to be worth spending so much effort on. Baldness doesn’t affect your quality of life.
The only reason men care so much is because long hair was often associated with nobility and power. Ancient gods or classical royalty were usually depicted with long luscious hair. Society has conditioned men to feel like less of a man if they lose their hair.
But that’s BS, bald is also a good look for men. Just embrace it. Isn’t it crazy that even if we came up with a “cure” for baldness, some men would still choose to be bald anyway?
Are you bald, or are you just imagining things? It affects your quality of life. Because I know a lot of people who struggle with baldness including some in my family, I take it seriously. If you think depression is worth spending time on, then baldness is worth spending time on too. Some people have a head shape that doesn't suit being bald, and they don't look good bald at all. In today's Western world, the majority of women won't choose a bald person if there’s a similar alternative with hair, it's simple biology. Only a minority of people look attractive bald. Good luck on dating apps being bald, seriously. You have no idea what you are talking about.
What you're saying is basically "Let them eat cake".
Here are some meta analysis + studies that support this:
"2024 mixed methods international survey paper summarizes prior experimental and cross sectional work and notes that studies often find more negative perceptions linked to baldness (e.g., being seen as older, less attractive, less successful)"
I’m a woman, not bald. And men always seem to overestimate the effect “head shape” has on their appearances.
Your face is the most attractive part of your head and is what people pay attention to. If you have a fucked up face, it doesn’t matter if you have the most perfect round skull. And if your skull is a little weird, it won’t matter if your face is genuinely attractive. And you could be a very hairy guy, but if your face is ugly, you’re still screwed.
Bald men struggle on dating apps, because almost all men struggle on dating apps. I have never encountered a man who claimed to have a really delightful experience with dating apps unless he was some ridiculously attractive type. Even in the best cases, they still admit it’s a grind.
If you’re depressed because you’re bald, treat your depression the way actually depressed people do. Exercise, socialize, connect to people. And if that doesn’t work, just take pills or whatever.
What you wrote is just vibes + armchair certainty. Hair loss measurably shifts how people are perceived (you can learn it if you read the studies I linked), and those shifts have downstream effects (dating, confidence, social treatment etc). Some guys look great bald, many don't and pretending "head shape doesn't matter" is silly. Hair frames the head and face. Take it away and you're exposing proportions people didn't notice before.
Your claim is basically "if I wouldn’t be upset, nobody should be" and that's not how humans work. Baldness is a real negative signal in a lot of contexts, and "everyone suffers on apps" doesn't erase disadvantages.
Acceptance is great, denial dressed up as pragmatism isn't.
I'm reminded of a girlfriend who patiently explained to me that your hair grows more if you brush it regularly because the brush "pulls it and encouraged it to grow". She said her mother had taught her that.
I thought it was nonsense. Shows what I know. I suppose folk wisdom is vindicated again.
Immediately had to think of Baron von Münchausen pulling himself out of a swamp by his own hair https://en.wikipedia.org/wiki/M%C3%BCnchhausen_trilemma
I just watched this for the first time last week and found it rather delightful.
[flagged]
You don't say. Seeing that Munchausen is a byword for telling tall tales.
Look at his handle… not that yc is for these novelty accounts
So hair grows by pulling itself upward? Perfect. I’m just going to stand under a ceiling fan and wait for my hair to pull itself back onto my bald spots. Science has finally given me a plan.
Just make sure you set the fan to "regrowth" mode and not "recede"
[flagged]
Put some mustard on your head and let a cow lick it dry... The pull will grow hair and the cow tongue will cleanse your aura.
irresponsible to not mention the risk of Cud Cap and Sympathetic Udder Syndrome. I even heard of one guy got Raging Horn
>the cow tongue will cleanse your aura
It's like that three-finger meme from the Tarantino movie, lol.
This points to a potential answer to a long standing question I've had about why some hairs stop growing at certain lengths. If the force is being generated by cellular migration then control over when to stop growing can be mediated by a signal that tells the cells to stop migrating, and that could be based on time or vibration amplitude or something else that correlates with hair length. For hair that grows continually you just ... never turn off cell migration.
I don't believe any hair on the human body truly grows continuously. Even head hair has a lifespan of ~7 years and whatever you can grow in that time is the max. I was a big metalhead in high school and grew my hair out. Indeed, after about 7-8 years it stopped getting longer, right at about waist level, and was stuck there until I finally got sick of it and cut it off.
I think they call this the "terminal length". As long as it will grow before it falls out.
Oh my god I have always asked why eyebrows stop growing and NOBODY ever thinks about it.
> why eyebrows stop growing and NOBODY ever thinks about it
If you clip your eyebrows, will they grow back to their original length? Or is there a process that generates an eyebrow hair and then stops after a pre-determined length of time (with periodic shedding)?
Every hair grows to a maximal length before stopping or falling out. It varies wildly based on genetics, location on the body, and body chemistry.
Animals evolved specialized hairs for different uses. Protection, warmth, display, your armpit hairs wick sweat and keeps your skin from rubbing. It's beneficial to have a system that keeps the specialized hairs in their optimal(ish) configuration and to replace hairs as they become worn and damaged.
Wait until you get older, and you either start trimming them or considering some kind of Yellowbeard style braids
So, the centrifugal force of head-banging is why metalheads grow long hair?
Or is that centripetal force? :)
Apologies for the "low effort" response:
https://xkcd.com/123/
Wow very interesting. This explains how goku turns level 3 as a super saiyan.
Tissot, N., Genty, G., Santoprete, R. et al. Mapping cell dynamics in human ex vivo hair follicles suggests pulling mechanism of hair growth. Nat Commun 16, 10267 (2025). https://doi.org/10.1038/s41467-025-65143-x
So if you shave your head your hair will grow slower?
And grass? What about grass?
I want to keep my favorite reply phrase: "Gras groeit niet harder als je eraan trekt." (Grass doesn't grow faster if you pull on it.)
Grass has a unique cell wall organization [1].
[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC5241289/
That feels like a pretty big clue that mechanics and motility are way more central to tissue dynamics than we give them credit for
I seem to remember there was a report about pulling on the hair of guinea pigs or some other small mammal encouraged hair growth.
How did this explain in-grown hairs?
Pulling doesn't have to happen at the surface?
Is this different from how hair grows on any other animal?
Are most industrial polymers drawn or extruded?
As I’ve ALWAYS suspected
I wonder if that's why it slows/stops growing when split ends are present. I've always wondered how that worked if it was pushing.
I don’t think this is relevant to that at all. This “pulling” is inside the skin still.
But I am also pretty confident that hair does not stop growing because of split ends. That feels like an “old wives tail”.
Presumably it's produced at the same rate but destroyed by drying out and cracking as it gets longer and has less access to oil, so it slows down and may find an equilibrium where it stays the same length.
Sure. If your hair is breaking off at the same rate it’s growing it’ll be a stable length. I have no idea if that happens though. It seems farfetched that hair would actually be splitting that’s aggressively unless it’s visibly very unhealthy.
If you take proper care of it (which includes trimming split ends so that the cracks don't propagate) then sure, but I've previously neglected my hair to the point where my split ends had split ends. I'll absolutely cop to "visibly unhealthy" but there does come a point where the ends start to fall apart and break off easily.
As someone with thinning hair, it's horrible how little study/research is being performed to understand how hair grows and treat hair loss. Most of the products on the market today were discovered by accident and have serious side effects. This condition impacts millions++ of people, yet everyone from physicians to pharmaceutical companies is fine with the status quo of "here, this may work for you" effectively woo medicine.
As someone who has lost at least 80% of his hair as an adult, I don't care about it at all. Get a short haircut and forget about it.
You aren't the only person with opinions on it though. Reminds me of the infamous HN thread where a (woman) poster mentioned offhand she and her husband were saving up for transplant for the sake of the survival of their marriage!
> Most of the products on the market today were discovered by accident and have serious side effects.
Topical minoxidil / finasteride has roughly zero side effects (due to the limited systemic exposure) and has something like a 90% efficacy rate. With 90%+ efficacy it's not a case of "this might work for you" it's "this will almost certainly work for you." It's cheap and it works.
Even oral 1mg finasteride has basically the same side effect profile after 1 year as placebo, side effects always* stop whether you stop taking it or continue taking it. And as an added bonus it significantly reduces your risk of low-grade prostate cancer (30% ish) while not increasing your risk of high-grade prostate cancer. Many of the side effects reported are in people taking 5mg doses for prostate hypertrophy, and the incidence of side-effects is dose dependent. Studies show that sexual side effects are primarily nocebo, if participants were told to expect them the rate was 3X higher than placebo, if they weren't told, they were about the same.
* the category of persistent side-effects has been defined primarily for data collection purposes, there's very little evidence for persistent side effects at all let alone a high incidence thereof. Many of the side effects people claim are related are things that would otherwise happen to you at the age you start to lose your hair regardless. It's good to collect more data though.
> As someone with thinning hair, it's horrible how little study/research is being performed to understand how hair grows and treat hair loss.
Given the size of the market I'd say there's a ton of research being done. It's just a tough nut to crack. There's some good data on PP405, for example.
> With 90%+ efficacy it's not a case of "this might work for you" it's "this will almost certainly work for you." It's cheap and it works.
Maybe for thinning hair only. If you're Norwood class 5–7, it won't help you unless you're a super responder (an outlier).
Yep, you have to start early; it regrows about 2-3 years of losses and prevents further losses.
The fact that we're only now uncovering fundamental mechanics like "hair is pulled, not pushed" kind of highlights how under-invested this area has been
As someone with a race in my head between white hairs and a receding hairline, hair loss does afflict millions of people, but it has no medical impact on people's life, beyond increasing the need to wear a hat when outside in the Sun for long. Is it that surprising that medical professionals would spend their time on other afflictions instead?
> it has no medical impact on people's life, beyond increasing the need to wear a hat when outside in the Sun for long
The impact on mental wellbeing can be pretty severe, though.
That sounds like a social concern, not a medical one.
A social concern where the path of least resistance toward resolution is probably effective medical advancements. For example, studies show bald men face greater challenges in both straight and gay dating in every country where it's researched (so it's not cultural context dependent).
Probably easier to figure out the follicular science than change universal attraction preferences.
Bill Gates kind of argued the other side of that in his old Malaria talk https://youtu.be/ZLkbWUNQbgk?t=258
It’s not really a big deal to be worth spending so much effort on. Baldness doesn’t affect your quality of life.
The only reason men care so much is because long hair was often associated with nobility and power. Ancient gods or classical royalty were usually depicted with long luscious hair. Society has conditioned men to feel like less of a man if they lose their hair.
But that’s BS, bald is also a good look for men. Just embrace it. Isn’t it crazy that even if we came up with a “cure” for baldness, some men would still choose to be bald anyway?
Jean-Luc Picard raised a generation of proud bald heads. We need to continue dreaming of a future where it doesn't matter.
I'd stay bald. I like the way I look. I think, conventionally speaking, I look more masculine without hair. It's all subjective.
Are you bald, or are you just imagining things? It affects your quality of life. Because I know a lot of people who struggle with baldness including some in my family, I take it seriously. If you think depression is worth spending time on, then baldness is worth spending time on too. Some people have a head shape that doesn't suit being bald, and they don't look good bald at all. In today's Western world, the majority of women won't choose a bald person if there’s a similar alternative with hair, it's simple biology. Only a minority of people look attractive bald. Good luck on dating apps being bald, seriously. You have no idea what you are talking about.
What you're saying is basically "Let them eat cake".
Here are some meta analysis + studies that support this:
https://pubmed.ncbi.nlm.nih.gov/37605428
"2024 mixed methods international survey paper summarizes prior experimental and cross sectional work and notes that studies often find more negative perceptions linked to baldness (e.g., being seen as older, less attractive, less successful)"
https://pmc.ncbi.nlm.nih.gov/articles/PMC11977830
I’m a woman, not bald. And men always seem to overestimate the effect “head shape” has on their appearances.
Your face is the most attractive part of your head and is what people pay attention to. If you have a fucked up face, it doesn’t matter if you have the most perfect round skull. And if your skull is a little weird, it won’t matter if your face is genuinely attractive. And you could be a very hairy guy, but if your face is ugly, you’re still screwed.
Bald men struggle on dating apps, because almost all men struggle on dating apps. I have never encountered a man who claimed to have a really delightful experience with dating apps unless he was some ridiculously attractive type. Even in the best cases, they still admit it’s a grind.
If you’re depressed because you’re bald, treat your depression the way actually depressed people do. Exercise, socialize, connect to people. And if that doesn’t work, just take pills or whatever.
What you wrote is just vibes + armchair certainty. Hair loss measurably shifts how people are perceived (you can learn it if you read the studies I linked), and those shifts have downstream effects (dating, confidence, social treatment etc). Some guys look great bald, many don't and pretending "head shape doesn't matter" is silly. Hair frames the head and face. Take it away and you're exposing proportions people didn't notice before.
Your claim is basically "if I wouldn’t be upset, nobody should be" and that's not how humans work. Baldness is a real negative signal in a lot of contexts, and "everyone suffers on apps" doesn't erase disadvantages.
Acceptance is great, denial dressed up as pragmatism isn't.
I'm reminded of a girlfriend who patiently explained to me that your hair grows more if you brush it regularly because the brush "pulls it and encouraged it to grow". She said her mother had taught her that.
I thought it was nonsense. Shows what I know. I suppose folk wisdom is vindicated again.
You should be able to test this by brushing one side of your head more than the other
But why did you think it was nonsense?
Curious if it works on beards, now.
Though, I would also somewhat expect pulling at it increases blood flow, which I would think to have some impact on growth?
Of course it works.
PS Love the bio!
Damn so it is possible to pull yourself up by your bootstraps.