[Biology] Hair health

I spent a while treating hair as a surface problem — something you fix with what you put on it. That was the wrong model. Hair is one of the first things your body defunds when it decides it’s short on resources, because a hair follicle is metabolically expensive and, from the body’s point of view, entirely optional. Nothing dies if you stop growing hair. So the follicle is a fairly honest readout of whether the rest of you is being fed, rested and left alone.

What follows is what actually moved the needle for me, in rough order of how much it mattered: sleep, then carbs, then the handstand thing, then not living in a permanent low-grade panic.

Contents

• Why hair is the first thing to get cut
• Sleep is most of it
  • Don’t train late
• Carbs — the part I had completely wrong
  • Protein: 80–90 g turned out to be enough
• Shirshasana
• Stress, and not rushing
• The ordering

Why hair is the first thing to get cut

Each follicle cycles through three phases. Anagen is active growth, and it lasts years — that’s why scalp hair gets long and eyebrow hair doesn’t. Catagen is a short shutdown, a couple of weeks. Telogen is rest, a few months, after which the hair sheds and the follicle starts over.

At any moment something like 85–90% of your scalp is in anagen. The failure mode that most people actually experience isn’t follicles dying — it’s follicles getting pushed out of anagen early, all at once, in response to some stress a few months back. That’s telogen effluvium, and its signature is the delay: you shed heavily in month three or four for something that happened in month zero. Which is exactly why it’s so hard to debug from the inside. By the time you notice, the cause is gone and you’re blaming your shampoo.

Two things follow from that. First, feedback on anything you change is slow — you’re looking at a three-month lag minimum, and closer to six before you can say anything confidently. Second, the intervention that matters is not “stimulate growth”, it’s “stop giving the follicle a reason to quit”.

Sleep is most of it

If I had to give up everything on this list but one, I’d keep sleep, and it isn’t close.

The targets I actually hold myself to are at least an hour of deep sleep and at least 2 hours 15 minutes of REM. Those aren’t magic numbers — they’re roughly what a genuinely full night produces for me, and they’re useful precisely because they’re not something you can fake by lying in bed longer.

The reason those two stages specifically: most growth hormone release happens in N3 deep sleep, and growth hormone is upstream of basically every tissue that has to rebuild itself on a schedule — which a follicle in anagen very much is. Deep sleep also front-loads into the first half of the night. REM does the other half of the job and concentrates in the back half, which is the part you amputate when you sleep six hours instead of eight. So a short night doesn’t shave a quarter off each stage evenly. It takes a specific bite out of the recovery machinery. I wrote about the stage breakdown in more detail in Importance of sleeping.

The other half of sleeping well is cortisol. Short sleep raises evening cortisol, and cortisol is one of the things that pushes follicles out of anagen. So bad sleep hits hair twice: less repair, more shutdown signal.

Don’t train late

This is the one change with the best ratio of effort to effect, and I resisted it for a long time because late evening was the only time I felt like training.

A hard session raises core temperature, heart rate and catecholamines, and all three have to come down before deep sleep will happen properly. Train at 10pm and you don’t lose sleep hours — you sleep the same seven and a half and just get less N3 out of them, which is the worst possible way to lose sleep because the clock still says you did fine. I could see it in the numbers before I could feel it.

Anything up to about three hours before bed is fine. Past that, either move the session earlier or accept that you’re paying for it.

Carbs — the part I had completely wrong

This is the finding I didn’t expect, and the one I’d most want to tell my past self.

I’d absorbed the ambient idea that carbs are the negotiable macro — the thing you cut first when you want to look better. What I’d actually built was a low-grade chronic energy deficit that I never labelled as one, because I was eating “enough protein” and felt fine.

Follicles don’t care about your macro philosophy. Anagen is one of the fastest-proliferating processes in the human body — hair matrix cells divide about as fast as anything you’ve got. That needs glucose, continuously. When total energy availability drops, the body triages, and hair loses that argument to your heart and your brain every single time. Low energy availability is a well-documented cause of hair shedding, and you don’t have to be anywhere near clinically underfed for it to bite.

The concrete change: 200 grams of sweet potato as a snack, most days. Nothing clever about it. It’s a genuinely large amount of carbohydrate landing at a time of day when I used to eat nothing, plus fibre, plus a pile of beta-carotene. My gym coach pushed me toward fibre specifically, and that turned out to matter more than I gave it credit for — a stable gut is doing real work here, both for absorbing the micronutrients that hair needs and for keeping the whole system out of inflammatory mode.

I’ve also gone back to walnuts. Zinc, biotin, omega-3s, vitamin E — but honestly the more likely mechanism is just that they’re a dense, easy source of calories and fat that I’ll actually eat without thinking about it.

Protein: 80–90 g turned out to be enough

The other correction. Hair is keratin, so protein obviously matters and severe deficiency will absolutely cost you hair. But I’d been treating protein as the thing to maximise, when the actual shape of it is a floor, not a slope. Once you’re over the floor, more protein does nothing for hair, and if the extra protein is displacing carbohydrate you’re making things worse, not better.

My coach put the number at 80–90 g and said stop optimising past it. That’s around 1.2–1.4 g per kilogram for me, which sits comfortably in the range you’d want for someone training regularly. Your number depends on your bodyweight and how much you lift, so don’t take mine literally — take the structure: hit the floor, then spend the remaining appetite on carbs.

The mental model that fixed this for me is that protein is the raw material and carbohydrate is the permission slip. Having bricks doesn’t help if the site is shut down for lack of funding.

Shirshasana

The third lever, and the one I hold most loosely.

I do a headstand and try to hold it for around 200 seconds. The theory is the obvious one — inverting floods the scalp with blood, and a follicle is fed by a capillary. Push-ups in the inverted position are a nice bonus if you can manage them; they’re a genuinely hard shoulder movement and the strength carries over to everything overhead.

Being honest about the evidence: I’m not aware of good data showing that inversions grow hair. Scalp blood flow is usually not the limiting factor for a healthy follicle, and in pattern hair loss the problem is hormonal sensitivity of the follicle itself, not plumbing. So I’d file this under “plausible, cheap, and it does other things I want anyway” rather than under “proven”.

What it definitely does: builds shoulder and core strength, forces a few minutes of stillness and controlled breathing, and — this is the part I actually value — you cannot be upside down and simultaneously worry about a deadline. Which brings us to the last thing.

If you’re starting from zero, don’t chase 200 seconds. Work up against a wall, and don’t do it at all if you’ve got neck or eye issues or high blood pressure without checking with someone qualified first.

Stress, and not rushing

Cortisol pushes follicles into telogen. That’s the mechanistic version, and it’s real — the shedding that shows up three months after a bad quarter at work is not a coincidence.

But the mechanism isn’t the interesting part. The interesting part is that the stress I was carrying was almost entirely about things I had no control over, which meant the worrying bought me exactly nothing and cost me sleep, appetite and hair. Deadlines you can’t move. Outcomes that depend on other people. Comparisons against people whose situation you don’t actually know.

The reframe that stuck: you were given this life, not lent it against a deadline. Rushing doesn’t get you there faster — it just means you were somewhere else in your head the whole time you were passing through. It’s worth sitting with how much you’ve already missed while being busy. Not as a guilt exercise; as a calibration of how expensive the hurrying actually is.

The ordering

If you only take one thing from this, take the ordering, because the ordering is where I was wrong for years:

sleep » carbs (then protein) > shirshasana

Sleep is not one item on a list of several; it’s most of the weight. Carbs were the thing I’d been unknowingly cutting, and adding them back mattered more than any supplement I’ve tried. Protein has a floor you should clear and then stop thinking about. The handstand is a nice-to-have that I do because it’s cheap and I like it.

And under all of it: give it time. You’re looking at a three-month lag before anything you change today shows up on your head, which is either infuriating or freeing depending on how you look at it. I’d argue freeing — it means the only sensible move is to fix the inputs and then stop checking the mirror.