Women's hormones
Why does hair thin in perimenopause? And which blood tests actually explain it
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed September 20266 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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Oestrogen falls in perimenopause, so your normal androgens are left with more say. Hair thins on top while the front hairline often holds. Thyroid trouble and low iron stores cause shedding too. No blood test proves the cause, but SHBG, testosterone, TSH and ferritin narrow it down. If the shedding is diffuse and recent, see telogen effluvium blood tests.
Find the test that reads these markers →As of September 2026. The NHS symptom list for menopause and perimenopause, last reviewed in May 2026, names “hair thinning or hair loss” outright. Hair supplements are marketed hard at this exact group, so it is worth knowing what a blood test can show first.
Your parting looks wider than it did. There is more hair on the pillow and more in the plughole. You are in your forties, your periods have changed, and nobody has joined the two things up. They are often joined up. The full list of perimenopause symptoms shows where hair sits among the rest.
1. Why does hair start thinning in perimenopause?
Oestrogen drops, and the hormones it used to balance get louder.
Androgens are a group of hormones that includes testosterone. Women make them normally, in small amounts. Oestrogen holds them in check. When oestrogen falls through perimenopause, that balance shifts, even if your testosterone number has not moved at all. Some hair follicles on the scalp are sensitive to androgens, and they respond by making finer, shorter hairs.
“FPHL is caused by a combination of genetic and hormonal factors.”
British Association of Dermatologists, female pattern hair loss
FPHL stands for female pattern hair loss. It has a shape you can recognise in the mirror. The same leaflet describes diffuse thinning over the top of the scalp, a mid part line that becomes more visible and widened, and a hairline at the front that often stays normal. It usually starts in the 50s or 60s, sometimes in the 30s or 40s.
Shedding that comes out evenly all over, rather than thinning on top, points somewhere else. That is worth knowing before you spend anything, because the two patterns lead to different markers.
2. Which blood tests actually tell you something?
Three groups of markers. Each one explains a different pattern.
- SHBG and the free androgen index. SHBG is the protein that carries sex hormones around and keeps them inactive. When it falls, more of your testosterone is free to act.
- Total testosterone. Read on its own it means little. Read next to SHBG it tells you how much is actually available.
- FSH and LH. These are the two signals your brain sends to the ovaries. They rise as the ovaries wind down, though they swing about while you are still having periods.
- TSH and free T4. TSH is the signal your brain sends to the thyroid gland. Thyroid trouble is a classic cause of even, all-over shedding.
- Ferritin. Ferritin is the protein that holds iron in reserve, so it shows how much iron you have banked. It is the most-cited marker in female hair loss.
On the thyroid, the numbers are larger than most people expect. A 2022 review in Cureus reports that diffuse shedding affects around 33% of people with an underactive thyroid and around 50% of people with an overactive one. If your loss is even rather than on top, start there.
On iron, the argument is about where the line sits. UK labs often flag ferritin only below about 15 µg/L. A 2002 review in Clinical and Experimental Dermatology recommended 70 µg/L for women with increased shedding, while saying plainly that the right level “is yet to be definitively established”. So a result of 25 can be called normal and still sit well under what that review asked for.
The same review is blunt about zinc. It found no evidence for the popular view that low zinc causes hair loss. That is one supplement claim you can put down.
Helvy's Hormone Balance panel (£99) carries FSH, LH, SHBG, total testosterone and the free androgen index. Ferritin sits on the Vitamins & Minerals panel (£159), alongside iron, transferrin saturation, vitamin D and B12. TSH and free T4 are on the General Energy & Wellness panel (£149). All three are home finger-prick kits.
3. What can a blood test not tell you?
Quite a lot, and being clear about it saves you money.
It cannot confirm perimenopause if you are over 45. NICE guideline NG23 says perimenopause in otherwise healthy women aged 45 or over should be identified from symptoms, without laboratory tests. FSH moves too much from week to week to settle the question. Our perimenopause blood test guide goes through that rule in full.
It cannot name the cause of your hair loss. A blood test measures biomarkers and offers wellness insight. It does not diagnose anything, and a qualified clinician reads your results next to your history. Two women with identical bloods can have very different scalps.
Oestradiol is not part of any Helvy panel. Oestradiol is the main form of oestrogen. If a clinician wants your oestrogen tracked directly, that is a conversation to have with them. Our oestradiol guide explains what the marker does.
Anaemia needs a full blood count, which we do not sell. Ferritin shows your iron stores. A full blood count shows whether the shortage has reached your red blood cells. That one is a GP test, and it is free.
4. When should you see a GP rather than buy a test?
Some patterns need a person looking at your scalp, not a number.
- Hair coming out in patches. That is a different problem from gradual thinning and needs assessing.
- A sore, scaly, itchy or scarred scalp. Female pattern hair loss leaves the skin looking normal.
- Loss that came on fast, over weeks. Illness, surgery, weight loss and severe stress can all trigger it.
- Thinning hair with new facial hair, acne and irregular periods. The dermatologists' leaflet names that combination as a reason to look further.
Treatments for female pattern hair loss exist, and the useful ones are a conversation with a GP or pharmacist. Do not start them off the back of a home test.
If hair is one of several things that have changed, our menopause hub covers the rest, and menopause or thyroid walks through the overlap that catches most people out.
READY TO TEST?
Start with the markers behind the pattern
The quiz asks what changed and when, then points you at the panel that fits. Results in around 5 working days from UKAS-accredited UK laboratories.
Frequently asked questions
Does perimenopause cause hair loss?
The NHS lists hair thinning or hair loss among the symptoms of menopause and perimenopause. As oestrogen falls, your androgens are left with more influence, and androgen-sensitive follicles on the top of the scalp make finer hairs.
Which blood tests should I ask for?
SHBG, total testosterone and the free androgen index for the hormone picture. TSH and free T4 for the thyroid. Ferritin for iron stores. A full blood count from your GP if anaemia is on the table.
Will my hair grow back after menopause?
It depends which kind of loss it is. Shedding triggered by illness, stress or low iron often recovers once the cause is dealt with. Female pattern hair loss tends to progress slowly instead, which is why the dermatologists advise seeing someone early.
What ferritin level do I need for healthy hair?
There is no agreed number. A 2002 review recommended 70 µg/L for women with increased shedding, while saying the right level is not settled. UK labs often flag only below about 15 µg/L, so a result can be called normal and still be low for hair.
Do hair supplements work in perimenopause?
It depends what you are short of. The 2002 review found no evidence that low zinc causes hair loss, and it warned against taking supplements with no proven deficiency. Knowing your iron and thyroid numbers first tells you whether there is anything to correct.
Related guides
Hair Loss Blood Test UK
The full marker list, for any cause of hair loss.
Perimenopause Blood Test UK
Which tests help, and why FSH alone cannot answer it.
Menopause or Thyroid?
The overlap that sends people down the wrong path.
Ferritin, Iron Studies & Your Results
How to read iron stores, not just haemoglobin.