Overview
Six hormones influence hair in women, and the useful framing is not "which one is abnormal" but which balance has shifted — because in the commonest presentation, every individual level is entirely normal.
| Hormone | What it does to hair | Worth testing? |
|---|---|---|
| Estrogen | Prolongs the growing phase; opposes androgen effect at the follicle | Where menopausal status is unclear |
| Testosterone | Converted to DHT in susceptible follicles, driving miniaturization | Yes — with SHBG, so free can be estimated |
| DHT | The active driver of pattern hair loss | Rarely useful to measure directly |
| SHBG | Binds testosterone. Low SHBG means more free, active hormone | Yes — it changes what the testosterone number means |
| Thyroid hormones | Both high and low cause hair loss | Yes, always |
| Prolactin | Raised levels affect hair and cycles | Where cycles are irregular |
The key insight: in the commonest pattern — thinning after menopause — androgens have not risen. Estrogen has fallen, so the same androgen level now acts with less opposition. Which is why a hormone panel in these women usually comes back unremarkable, and why a normal result does not mean hormones are uninvolved.
Estrogen, and what its loss does
Estrogen prolongs the anagen phase — the growing part of the hair cycle. More time growing means longer, thicker hairs and more of them in growth at once.
This is why hair often looks its best in pregnancy, when estrogen is high, and why postpartum shedding is so pronounced when it falls.
Through menopause the same mechanism runs slowly: shorter growing phases, shorter and finer hairs, and reduced opposition to androgen activity at susceptible follicles. Estrogen also supports the scalp tissue itself and sebum production, which is why hair frequently becomes drier and more brittle alongside becoming thinner.
Androgens, stated accurately
The widely repeated version — that androgens surge after menopause and attack the hair — is wrong, and the accurate version explains more.
Female androgen levels decline gradually with age. What changes is the ratio. Estrogen falls faster and further, so the androgens that remain have proportionally more effect.
At the follicle, testosterone is converted by 5-alpha reductase into dihydrotestosterone, which binds androgen receptors in genetically susceptible follicles and progressively shortens each growth cycle. The follicle miniaturizes over years — this is the mechanism of pattern hair loss, and it is why the condition is genetic in susceptibility and hormonal in expression.
Measuring DHT directly is rarely useful, because what matters is receptor sensitivity and local enzyme activity in the follicle, not the circulating level. This is worth knowing because DHT panels are sold on the assumption that the number is actionable, and generally it is not.
Why SHBG changes the interpretation
Most circulating testosterone is bound to sex hormone binding globulin and inactive. Only the free fraction reaches receptors.
So two women with an identical total testosterone can have very different free testosterone, depending on SHBG — and it is the free fraction that acts on the follicle. A testosterone result without SHBG alongside it is difficult to interpret.
SHBG falls with insulin resistance and with higher body weight, and rises with oral estrogen and with thyroid overactivity. Which means insulin resistance can raise free testosterone without total testosterone changing at all — a genuinely common and frequently missed contributor. What SHBG is and what moves it.
Thyroid and prolactin
Thyroid is worth testing in every case, without exception. Both underactive and overactive thyroid cause hair loss, hypothyroidism peaks in exactly this age group, and it is straightforward to detect and treat. Which test does what.
Prolactin is worth checking where cycles are irregular or where there is nipple discharge. Raised prolactin suppresses the reproductive axis and has specific causes — including some medications and, less commonly, a pituitary adenoma — that need identifying rather than treating around.
When the pattern points to something specific
Ordinary pattern hair loss in a woman comes with a normal hormone panel. A few combinations point elsewhere and are worth naming.
Thinning with irregular cycles, acne and unwanted facial hair suggests a genuine androgen excess — polycystic ovary syndrome most commonly, and it frequently comes with insulin resistance that is itself worth addressing.
Rapid onset with marked facial hair growth, voice deepening or clitoral enlargement is a different situation entirely and needs prompt assessment, because it can indicate a hormone-producing tumor. Rare, and specifically the reason the pattern is asked about.
Thinning alongside significant fatigue, weight change and cold intolerance points at thyroid before it points at androgens.
What we would test, and what we would not conclude
A reasonable panel: total testosterone with SHBG, thyroid function, prolactin where cycles are irregular, ferritin — which is not hormonal and is the single most commonly correctable finding — plus vitamin D, and estradiol and FSH where menopausal status needs clarifying. Cycle timing matters for several of these.
What we would not conclude from a normal panel is that hormones are irrelevant. In female pattern hair loss the levels are usually normal and the problem is follicle sensitivity and the shift in balance — neither of which a blood test measures.
And what we would not do is treat a hormone level because hair is thinning, when the level is not itself abnormal.
Frequently asked questions
Which hormone causes hair loss in women? No single one. The commonest mechanism is falling estrogen leaving normal androgen levels less opposed at genetically susceptible follicles. Thyroid disease and raised prolactin are separate, testable causes.
Should I get my DHT tested? Rarely useful. What matters is follicle sensitivity and local enzyme activity rather than the circulating level, so the number seldom changes management.
My hormone panel was normal but my hair is thinning. What does that mean? That is the usual finding in female pattern hair loss. The levels are normal; the follicle response and the estrogen-androgen balance are what changed.
Does hormone therapy help hair? It is not a hair loss treatment and is not prescribed as one. Some women notice improvement, plausibly through the balance, and the evidence for it as a hair intervention is limited.
What if I also have acne and irregular cycles? That combination points toward a genuine androgen excess and is worth investigating specifically rather than treating as ordinary pattern loss.
Where this fits in your plan
The useful panel here is short: testosterone with SHBG, thyroid, prolactin where indicated, and ferritin — read together, against the pattern of loss and against your cycles rather than against a range.
And read by someone willing to say when the panel is normal and the answer lies in follicle sensitivity rather than in a number worth treating. What we check.
We measure first. Then we act.
Diagnostic testing does not diagnose or rule out disease on its own and is interpreted by a licensed provider alongside your history and examination.
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This article is educational and is not medical advice. Treatments are available only to eligible patients following clinical evaluation and within applicable regulations. Individual results vary.
