A patient I'll call Helen, 52, brought a sandwich bag to her appointment. It was full of hair from one week of showers. Her hairdresser had told her she was "over-washing".

She wasn't. Here is what was actually happening under her scalp.

Every hair on your head grows from a follicle, and every follicle runs a cycle: a growing phase that lasts years, a short resting phase, then the hair falls and a new one starts. For most of your adult life, oestrogen has been quietly doing one job in that cycle  keeping follicles in the growing phase for longer. The follicle has oestrogen receptors of its own; it's a direct target for the hormone, not a bystander (Ohnemus et al., Endocrine Reviews, 2006).

Oestrogen doesn't taper off politely when the menopause hits. It falls hard, and it keeps falling. When that signal weakens, more follicles drop out of the growing phase early. That's the shedding. But the part nobody explains is what happens next: each time a follicle restarts without that support, it comes back slightly smaller. The hair it makes is finer, shorter, paler. Dermatologists call it miniaturisation.

That's why you're seeing two things at once  hair in the drain and a parting you can see through. It isn't damage. It's follicles shrinking, one cycle at a time.

Helen's hair wasn't over-washed. It was under-signalled.

And here's the frustrating part: none of this shows up on a blood test  even when someone bothers to run one.

Helen had been to her GP. Bloods done. Everything "normal". Sent away.

I looked at the same results and saw three things that were making Reason 1 worse.

Her ferritin was 31. The lab range said normal. The hair-loss literature says otherwise: the threshold repeatedly recommended for women with hair shedding is a ferritin of at least 70 ng/mL (Trost, Bergfeld & Calogeras, Journal of the American Academy of Dermatology, 2006). Perimenopause is exactly when ferritin collapses — the heavy, unpredictable periods of your mid-forties drain iron faster than you replace it. At 31, her follicles were being told there wasn't enough iron to justify growing hair.

Only her TSH had been checked. That's the standard panel. It misses a lot. In one of the largest thyroid-screening studies ever run, roughly 1 in 10 adults had an undetected thyroid abnormality  more common in women, and rising with age (Canaris et al., Archives of Internal Medicine, 2000). A sluggish thyroid slows every follicle's cycle. The tell-tale signs are the ones women describe to me as "straw-like" hair and eyebrows thinning from the outer ends.

She was waking at 3 am, every night. Night sweats, then lying there. Chronic broken sleep keeps cortisol high, and sustained stress is one of the best-documented triggers for pushing follicles into their resting phase en masse  what we call telogen effluvium (Peters et al., American Journal of Pathology, 2006). Then the stress of losing your hair drives the cortisol higher. It's a loop.

So: three separate brakes on the follicle, and a results sheet that said "normal" on every line.

If you take one practical thing from this article: ask your GP for a ferritin level and a full thyroid panel, and say the words "hair loss" when you ask. It's free. Do it.

But correcting all of that takes months  and for some women the hair doesn't fully come back on its own. Which is why, in the meantime, they buy things. And this is where it goes wrong.

The strand of hair you can see and touch is dead keratin. It left the follicle finished. Nothing you put on it can change what the follicle does next.

That single fact explains most of the disappointment in my consulting room.

Thickening shampoos and masks coat the strand so it feels fatter for a wash or two. They do nothing underneath.

Biotin. True biotin deficiency is rare, and the evidence for biotin improving hair in women who aren't deficient is, to put it kindly, thin (Patel et al., Skin Appendage Disorders, 2017). It's a very popular way to spend £12 at Boots.

Rosemary oil. There is one small study, from 2015, in men, comparing it to minoxidil. That's the whole evidence base for the thousands of TikTok videos.

Oral iron. Useful if your ferritin is low  but slow, hard on the stomach, and it does nothing for the oestrogen problem in Reason 1.

None of these are scams. They're just aimed at the wrong place. You've been buying things for the hair, when the thing that's failing is the follicle.

So the question I ended up asking was simpler than I expected: can a follicle that has gone quiet be told to start again? It turns out it can  and the research came from a surprising place.

A miniaturised follicle isn't dead. It's dormant. Small, under-instructed, but still there. And cells that are still there can still receive instructions.

Two categories of ingredient do exactly that.

Peptides are short chains of amino acids that act as messengers. Skin cells recognise them and respond — certain peptides, copper peptides in particular, have been studied for their ability to stimulate follicle activity and improve the tissue around it. They don't feed the hair. They talk to the cells that make it.

PDRN  polydeoxyribonucleotide  is a fragment of DNA, originally derived from salmon, that has been used for years in Korean and Italian regenerative medicine to speed up tissue repair. More recently it's been studied on the scalp, for the same reason: it encourages the cellular activity a dormant follicle has stopped doing on its own.

I'll be honest that this research is younger than I'd like. But it's the first category of ingredient I've seen that goes at the actual problem from Reason 1 — the follicle's signalling  instead of dressing the symptom.

There was a catch, though. And it's the reason most "peptide serums" in Boots do nothing either.

Your scalp is a barrier. That's its job: keep things out. The outer layer is built to stop anything reaching the follicle underneath.

Now think about how you apply a serum. A few drops on your fingertips, then you rub. Most of it coats the lengths  dead hair, Reason 3. Some evaporates. The rest ends up on your pillowcase. The follicle you were aiming at gets a trace, if that.

Clinics solve this with micro-needling: a roller of tiny needles that opens temporary micro-channels in the scalp so active ingredients can actually get in. It works  studies on micro-needling plus a topical show meaningfully better results than the topical alone. It also hurts, draws blood, and costs £150–£300 a session.

So what I wanted for my patients was two things:

1. Something that parts the hair and puts the product on the scalp not on the lengths.
2. Something that opens micro-channels without needles, blood or a clinic appointment.

Peptides and PDRN, delivered into the scalp, at home, in a couple of minutes.

For about a year, I couldn't find it.

What I now recommend

Then a patient came back for a follow-up with a tube in her bag, and asked me what I thought of it.

It was a PDRN and peptide serum applied through a brush head. Thirty-eight bristles part the hair and place the serum directly on the scalp. And the serum itself contains what the manufacturer calls "reedle shot"  microscopic mineral spicules, derived from marine sponge, that create temporary micro-channels on contact. Cold, tingling for about a minute, then absorbed. No needles. No blood. Two minutes a day.

That's Klyver. It's what I'd been describing above without knowing it existed.

In the order this article has laid out:

— Peptides and PDRN signal the dormant follicle (Reason 4)
— The brush puts them on the scalp, not the dead hair (Reason 5)
— The spicules carry them through the barrier — the manufacturer's data puts uptake at roughly ten times that of fingertip application

I won't tell you it works for every woman. Here's what I do tell my patients: a full hair cycle takes time, so give it 8 to 12 weeks, and photograph your parting on day one so you have something honest to compare against.