You are five months into a jar of 10,000 microgram biotin. You always buy the same one, because switching felt like wasting the time you had already put in. The shower drain looks exactly the same, and the question in your head is the same one as always: “maybe it just needs longer?”
It does not need longer. Five months is enough time for a corrected nutrient to show up in your hair. If nothing has changed, the most likely explanation is the one nobody is selling: biotin was not what was missing.
And here is the part the label leaves out. A supplement is not fertiliser. It only restores performance when something is actually lacking, and you cannot find out what is lacking by looking at your hair. You find out in your blood, with tests ordered and interpreted by a doctor.
Hair has a speed, and it is not negotiable
Hair grows about a centimetre a month. That rate is set by the activity of the follicle, not by how many vitamins are on your plate. With adequate nutrition, the follicle is already running at its ceiling.
Which is why “accelerating growth” is a structurally impossible promise. What a supplement does, when it does anything, is release a brake. If no brake is on, there is nothing to release.
Biotin (vitamin B7, also called vitamin H) is involved in keratin production. That much is true, and it is exactly what the advertising leans on. What the ad leaves out is the second half of the sentence: the intake considered adequate for adults is around 30 micrograms a day, and it is in eggs, liver, nuts, pulses and bananas. Genuine biotin deficiency is rare in people who eat food.
When it does happen, there is an identifiable cause: an inherited deficiency of the enzyme biotinidase, bariatric surgery and other malabsorption syndromes, long-term use of certain anticonvulsants, chronic alcohol use, or a habit of eating raw egg white (avidin, a protein in the white, binds biotin and blocks its absorption).
A review published in 2017 gathered the reported cases of hair and nail improvement with biotin. Every one of them had one of those underlying causes behind it. For people without a deficiency, there is no evidence of benefit.
10,000 micrograms is not better, and it has a side effect nobody mentions
Hair jars usually come in 5,000 or 10,000 micrograms. That is more than a hundred times the adequate intake. Biotin is water soluble, the excess leaves in your urine, and that is not the part that worries anyone.
The problem is in the laboratory. Many blood tests use the bond between biotin and a protein called streptavidin as part of how they measure. Biotin circulating at a high concentration competes in that reaction and distorts the result, upwards or downwards depending on how the assay is built.
The FDA, the American regulatory agency, published a safety alert about this in
- The affected tests include troponin (the marker used to investigate a heart
attack), TSH and free T4 (thyroid function), vitamin D, PTH, hCG and ferritin. The agency reported one death linked to a falsely low troponin result.
Notice the irony: ferritin is the single most important test in the investigation of hair loss in women. The supplement you are taking because of the shedding can blur the exact measurement that would explain the shedding.
Doses from 5 milligrams a day (5,000 micrograms) are already enough to interfere. If you take biotin and you have blood drawn, stop two to three days beforehand and tell both the laboratory and your doctor. That piece of information changes how the result is read.
What is worth measuring before you buy any jar
| Nutrient | What a deficiency does to hair | How it is checked | Supplementing with no deficiency |
|---|---|---|---|
| Iron | Diffuse shedding, finer hair, common in menstruating women | Ferritin, full blood count, transferrin saturation | Useless, with a risk of overload |
| Vitamin D | Associated with effluvium and alopecia areata in observational studies | 25-OH vitamin D | No benefit; high doses are toxic |
| Zinc | Shedding, brittle hair, flaking | Serum zinc | Above 40 mg a day it blocks copper absorption and makes shedding worse |
| B12 and folate | Affects cell division in the follicle | B12, serum folate | No effect |
| Thyroid (not a nutrient) | Diffuse shedding, dry hair with no body | TSH and free T4 | Not a supplement issue; it needs medical treatment |
| Biotin | Shedding and brittle nails, in a rare deficiency | Assay rarely available; the cause is investigated instead | No benefit, and it interferes with the tests above |
One honest caveat about ferritin: below 30 ng/mL the literature treats it as iron deficiency even when haemoglobin is normal. Part of the trichology literature works with higher targets, between 40 and 70, specifically for hair. That higher cut-off is debated and is not a consensus. The person who decides what to do with your number is your doctor, with your history in hand.
More is not better: three nutrients where the excess brings hair down
Too much vitamin A causes shedding. The upper limit for an adult is around 3,000 micrograms of retinol a day, and a multivitamin plus a dermocosmetic plus cod liver oil goes past that without trying.
Too much selenium causes shedding and brittle hair. Brazil nuts are very high in selenium, and “two a day” repeated for months gets close to the limit on its own.
Zinc at a high dose brings copper down, and copper deficiency also shows up in hair. It is the classic case of solving one problem by creating another.
Why it worked for your friend
Two explanations, and neither of them is the biotin.
The first is the calendar. The shedding that frightens most women is telogen effluvium: a block of follicles goes into rest at the same time and lets go two to three months later. That pattern has its own curve and tends to resolve in three to six months. Anyone who starts taking something at the peak of the shedding is starting exactly when the curve was about to turn on its own.
The second is the formula. These jars rarely contain biotin alone. They contain iron, vitamin D, zinc. If your friend’s ferritin was 12, she did improve, and she improved because of the iron, at a dose a doctor would have calibrated better.
The useful question is not “which supplement should I take”. It is “what is missing, and how much”.
When it is a medical matter, not a cosmetic one
See a dermatologist before taking any supplement if there is a bald patch with a sharp edge, smooth shiny scalp where nothing grows any more, a sore, a crust or pain, shedding alongside changes in weight, menstrual cycle or nails, or shedding that has gone past twelve months with no sign of regrowth. Signs of excess male hormone (excess body hair, late-onset acne, a changing voice) also call for clinical investigation, not a jar.
Hair therapy works on the terrain: the scalp, inflammation, flaking, the quality of the hair that is coming through. Nutritional deficiency and systemic disease belong in a different consulting room, and the two jobs sit together well.
What to do with what you have just read
Read the label of whatever you are already taking and add up the biotin from every source. If it comes to more than 5,000 micrograms, you have a new piece of information to bring your doctor before your next blood test.
Book an appointment and ask for the investigation: full blood count, ferritin, transferrin saturation, TSH, free T4, 25-OH vitamin D, zinc, B12. With the results in hand, the decision about supplements stops being a guess.
And write down the date the shedding started. That number is worth more than the label on the jar.
If you would like to talk about your case
The trichoscope assessment does not replace a blood test and it is not a medical diagnosis. It answers a different question, one blood cannot answer: what is happening on your scalp right now, with a magnified image, hair density per area, thickness, the state of the follicular openings and the degree of flaking. You follow the trichoscopy on screen, together with the professional, while it is being done.
That measurement is what separates shedding with a predictable end from progressive thinning, and what decides whether it makes sense to treat the terrain while the clinical investigation runs in parallel.
It costs R$200 (Brazilian reais), credited in full towards the protocol. We measure again during or at the last session and compare with the image from the first day, at no additional cost. Bring any test results you already have, even old ones.
We are in Tatuapé, in the East Zone of São Paulo, near the Carrão and Tatuapé metro stations, Tuesday to Saturday, 9am to 6pm, by appointment. Tuesday is the day reserved for scalp therapy. English is spoken here: mention it when you book.