When thyroid disease, androgen excess, pregnancy or other hormonal changes may contribute to hair loss, and how to decide which tests are useful.
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The same hormonal signal can have different effects in different places. Androgens help a beard develop while contributing to miniaturisation in susceptible scalp follicles. The hormone alone is therefore only part of the explanation; the tissue receiving the signal matters.
This is why a blood test cannot tell the whole story of someone’s hair. It measures what is circulating, not every process happening inside the follicle. Equally, the fact that hormones influence hair does not mean everyone needs an extensive hormone panel.
Testosterone is converted into DHT by an enzyme called 5-alpha reductase. In male pattern hair loss, DHT contributes to progressive miniaturisation of genetically susceptible follicles. Most affected men have hormone levels within the normal range.
Female pattern hair loss is less uniformly dependent on androgens. Some women have androgen excess, many do not, and other mechanisms contribute. A normal result does not rule out the diagnosis, while an elevated result needs interpreting in the context of the whole person.
Lowering DHT can help appropriately selected patients, but this is a treatment decision with potential adverse effects. It is not a general instruction to reduce a normal hormone as far as possible.
Scalp thinning together with increased facial or body hair, persistent acne or irregular periods can justify an assessment for androgen excess. One possible cause is polyendocrine metabolic ovarian syndrome (PMOS), previously called PCOS. The name changed in 2026; you will still encounter both terms in clinics and research.
Hair loss alone does not diagnose PMOS. Assessment may involve menstrual history, clinical signs, appropriate blood tests and consideration of other causes. The wider implications for metabolic and reproductive health matter as well as the hair.
Rapidly developing facial hair, a deepening voice or other pronounced changes need prompt medical review. These should not automatically be assumed to be a familiar hormonal condition.
Pregnancy often reduces shedding by keeping more hairs in the growing phase. After childbirth, many follicles change phase around the same time. The resulting shed appears months later and usually recovers gradually.
Hair can also become thinner around menopause, but ageing, genetics and other health factors overlap with hormonal change. It is too simple to attribute every case to low oestrogen or promise that replacing it will restore density.
Menopausal hormone therapy and contraception should be chosen for their wider clinical indications, benefits and risks. They are not routine hair-growth treatments. If a change followed starting or stopping a hormonal medicine, discuss the timeline with the prescriber instead of altering it yourself.
Both an underactive and an overactive thyroid can cause diffuse shedding. Changes in energy, weight, temperature tolerance, bowel habits or heart rate may provide clues, but symptoms alone cannot establish the diagnosis.
Blood tests can identify thyroid dysfunction when it is suspected. Treating a thyroid disorder may help the hair recover, although visible improvement can lag behind blood results. Continued thinning may also reflect a second condition rather than treatment failure.
Postpartum thyroiditis is particularly easy to miss because fatigue, anxiety and disrupted sleep can be attributed to new parenthood. Mention symptoms beyond the hair if they are persistent or feel out of proportion.
Significant illness or stress can precede telogen effluvium. That does not mean a commercial cortisol test will identify the cause of ordinary thinning, or that a product claiming to “reset cortisol” is an evidence-based hair treatment.
Other endocrine tests may be appropriate when there are specific clues. For example, unexpected milk discharge or menstrual disturbance can justify considering prolactin. Hair loss alone is a weak reason for testing every hormone.
Studies have also linked pattern hair loss with some metabolic conditions, but an association does not prove that one causes the other. Blood pressure, diabetes risk and general health deserve attention on their own merits, without promising that improving a blood marker will necessarily reverse miniaturisation.
A useful test has a reason behind it and a plan for what to do with the result. Tell your clinician about symptoms, medicines, supplements and recent hormonal changes. High-dose biotin supplements can interfere with some laboratory tests, so the laboratory needs to know if you take them.
When a genuine endocrine disorder is found, treat it. When the diagnosis is pattern hair loss with normal circulating hormones, treatment can still be discussed. The aim is an explanation that fits your hair and your health, rather than a search for a number to “optimise”.
