You noticed more hair in the drain, more hair in the brush, and the ponytail that used to take three turns of the elastic now takes four. You saw a doctor, had blood drawn, and the answer came back in a single sentence: “your blood count is normal”.
You left without an explanation, and the shedding carried on exactly as before.
The trouble is that a normal blood count and healthy iron levels are two different statements. Only one of them is on that piece of paper, and it is not the second one.
A blood count measures what is circulating, not what is stored
The body treats iron as a till and as a savings account. The haemoglobin inside your red blood cells is iron in use, in circulation. Ferritin is the protein that stores iron at rest, in the liver, the spleen, the bone marrow. A blood count looks at the till. Ferritin looks at the savings.
The savings empty first. Iron loss happens in stages, and the stages come in order:
| Stage | What has already happened | Ferritin | Haemoglobin on the blood count |
|---|---|---|---|
| 1. Stores falling | The reserve is being spent to keep production normal | Low | Normal |
| 2. Production affected | There is not enough iron to build new red cells, but the books still balance | Low | Normal or at the bottom of the range |
| 3. Iron deficiency anaemia | The books no longer balance | Low | Below the reference range, with smaller red cells (reduced MCV, the mean corpuscular volume) |
The blood count only flags a problem at stage 3. In the first two it comes back normal, and it comes back normal honestly: it is measuring exactly what it was designed to measure.
There is an aggravating detail nobody mentions. The reference range for haemoglobin is wide. A woman whose usual value is 13.8 g/dL can drop to 12.2 and still be “within normal”, having already travelled a third of the way to anaemia. The lab compares you with the population. Nobody compares you with you.
Why hair feels it before blood does
The follicle matrix is among the fastest dividing tissues in the human body. To divide a cell you have to copy DNA, and the enzyme that sets the speed limit on that copying, ribonucleotide reductase, needs iron to work.
When iron runs short, the body triages. Red blood cells, muscle and brain come first. Hair is not on the priority list of any species that needs to survive, and that is precisely where the cut shows up: the follicle shortens its growth phase, new hair comes in finer, and a block of follicles drops into rest at the same time.
Which means shedding can be the first symptom of a deficiency the blood count cannot see yet. This is not hair being dramatic. It is hair being the first thing switched off.
A “normal” ferritin can mislead too, and here is the trick
Ferritin has a second job: it rises with inflammation. A recent infection, active inflammatory disease, liver disease, heavy alcohol use and obesity all push the number up without a single extra gram of stored iron.
In practice: a ferritin of 45 in someone with active inflammation can be an empty store in disguise. That is why a serious investigation does not ask for ferritin on its own. It comes alongside C-reactive protein (a marker of inflammation) and transferrin saturation, which shows how much of the blood’s iron transporter is actually loaded. A saturation below 20% with a seemingly acceptable ferritin is one of the signals that changes the reading.
On where the cut-off sits, honesty is worth more than tidiness. The World Health Organization treats ferritin below 15 ng/mL as depleted stores in an adult woman, much of the clinical literature uses 30, and part of the trichology literature argues for higher targets, between 40 and 70, with hair specifically in mind. That higher figure is debated and is not a consensus. The person who decides what your number means is your doctor, with your history in hand, not a table on the internet and certainly not a salon.
Why you should not buy the bottle and start on your own
This is the uncomfortable part of the conversation, and it is the part that matters.
Low iron in an adult is a sign, not a diagnosis. The clinical question is not “how much to replace”, it is “where is it going out”. In a woman who menstruates, heavy menstrual bleeding is the most common cause, and plenty of people live with a heavy flow believing it is simply normal for them. But there is also coeliac disease, gastritis from Helicobacter pylori (the bacterium associated with ulcers), previous bariatric surgery, chronic anti-inflammatory use, small and constant bleeding somewhere in the digestive tract. After menopause, low iron calls for a digestive investigation, because it can be the first clue to a lesion that has been bleeding a little for a long time. Supplementing on your own fixes the number and leaves the cause working in silence, sometimes for years.
Dosing does not work the way intuition says it should. Each dose of iron raises hepcidin, the hormone that shuts down intestinal absorption, and that block lasts around a day. Taking it several times a day can absorb proportionally less than a single morning dose or dosing on alternate days. Calibrating that belongs to whoever writes the prescription.
Side effects are common, and one of them has a perverse twist. Constipation, nausea and stomach pain make a lot of people abandon treatment in the second week. Iron also darkens the stool, which is harmless in itself but muddies exactly the signal that would point to digestive bleeding.
Excess iron has no exit door. The body has no efficient route for excreting iron, and the surplus deposits in the liver, heart and pancreas. There is also a specific trap: thalassaemia trait also produces small red cells and is routinely mistaken for iron deficiency. In that case supplementation solves nothing and piles up iron in someone who did not need it.
Hair runs on its own calendar, not yours
Assume the best case: your doctor finds the cause, treats it, and ferritin climbs. Hair does not answer in two weeks.
Refilling stores takes months. After that, the follicle has to come out of rest and return to its growth phase, and new hair grows about a centimetre a month, a little under half an inch. For the first few weeks, what you see in the mirror is still the old wave finishing its fall.
Which is why the mirror is a poor instrument for assessing shedding, and a phone camera is worse. What separates improvement from impression is a repeated measurement, at the same point on the scalp, at the same magnification.
Where a salon fits, and where it does not
Hair therapy does not measure iron, does not read blood work as a diagnosis and does not treat nutritional deficiency. That belongs in a doctor’s office.
What the trichoscope does is measure the scalp: hair density per square centimetre, the calibre of each hair, how much calibre varies between hairs, the state of the ostia (the pores the hair comes out of) and signs of inflammation around the follicle. That measurement separates two things that look identical in the mirror: diffuse thinning without miniaturisation, a pattern consistent with a shedding episode and with systemic causes such as low iron, and progressive miniaturisation, which is a different picture with a different outlook.
That information is useful for the conversation with your doctor, and useful for knowing whether what you are doing to your scalp is accomplishing anything.
See a dermatologist before anything else if there is a patch with a sharp border, smooth shiny scalp where nothing grows any more, a sore, crusting or pain, shedding alongside changes in weight, menstrual cycle or bowel habit, or shedding that has gone past twelve months without recovery. And see a gynaecologist if your menstrual flow requires changing protection every hour, lasts more than seven days, or comes with large clots.
What to do with what you have just read
Three things, in this order.
Book an appointment and bring the question in writing: “my blood count is normal, but what is my ferritin and my transferrin saturation?”. Asking by name changes the conversation.
If you take a supplement containing biotin, stop it two to three days before the blood draw and tell the lab. High-dose biotin interferes with the assay method for several tests, ferritin among them.
Write down the date the shedding started, and whether anything changed in your menstrual flow, diet, surgery or medication in the six months before. That timeline is worth more to a doctor than any description of your hair.
If you would like to talk about your case
The hair assessment with a trichoscope measures density, calibre and variation in calibre, which is what makes it possible to follow a scalp by numbers instead of by impression. You follow the trichoscopy on screen, together with the professional, as the images come up. There is no report, no written findings and nothing handed over on paper: it is a conversation with the measurement in view.
R$200 (Brazilian reais), credited in full towards the protocol. We measure again at the same points during or at the last session and compare them with the image from the first day, at no extra cost.
Tuesday to Saturday, 9am to 6pm, by appointment, in Tatuapé, in the East Zone of São Paulo, near the Carrão and Tatuapé metro stations. Tuesday is the day reserved for scalp therapy. We offer service in English. If you already have blood work in hand, bring it: it helps make sense of what the images are showing.