Short answer: Hirsutism is caused by androgens, hormones such as testosterone, acting on hair follicles that are sensitive to them. In about 7 out of 10 women who see a specialist for it, the underlying cause is PMOS, the condition called polycystic ovary syndrome (PCOS) until 2026. Less common causes include an inherited adrenal condition, medications and, rarely, hormone-producing tumors. In some women no hormone problem is found at all. Hirsutism also tends to run in families.
Knowing the cause of your hirsutism matters, because it decides which treatment will work and whether you need any further tests. This article explains what happens inside the hair follicle, goes through the causes from most to least common, and answers a question many readers ask: is hirsutism hereditary?
What happens in the hair follicle
Most of the body is covered in fine, light vellus hair. In certain areas, including the upper lip, chin, chest, abdomen, back and thighs, the follicles respond to androgens. Androgens make these vellus follicles develop into terminal follicles, which produce coarse, dark hair. Inside the follicle, the enzyme 5α-reductase converts testosterone into dihydrotestosterone (DHT), a more potent androgen.[1]
Two factors decide whether this happens:[1]
- How much androgen is circulating. Higher levels of testosterone and other androgens increase the signal reaching the follicles.
- How sensitive the follicles are. Follicle sensitivity varies from person to person. This is why some women develop hirsutism with normal androgen levels in their blood, while others with high levels have little extra hair.
Even women with very high androgen levels, from PMOS or an adrenal condition, may not develop hirsutism.[2]
The causes of hirsutism, from most to least common
The best data come from a study of 950 women referred to two endocrine clinics in Palermo, Italy, because of signs of androgen excess, which in most cases meant hirsutism.[3]
| Cause | Share of patients | What it is |
|---|---|---|
| PMOS (formerly PCOS) | 72.1% | A hormonal and metabolic condition in which the ovaries produce more androgens |
| Idiopathic hyperandrogenism | 15.8% | Raised androgen levels with regular cycles and no other cause found |
| Idiopathic hirsutism | 7.6% | Hirsutism with normal androgen levels and regular cycles |
| Non-classic congenital adrenal hyperplasia (NCAH) | 4.3% | An inherited enzyme problem that makes the adrenal glands overproduce androgens |
| Androgen-secreting tumors | 0.2% | Rare tumors of the ovary or adrenal gland |
These figures come from specialist clinics, so they don’t describe every woman with extra hair. Still, the order is consistent: the Endocrine Society guideline also states that 70-80% of women with hirsutism have PMOS.[1]
PMOS (formerly PCOS)
PMOS is diagnosed in adults when at least two of these are present: signs of androgen excess (such as hirsutism or high testosterone), irregular cycles or ovulation problems, and polycystic ovaries on ultrasound or a high anti-Müllerian hormone (AMH) level.[4] Insulin resistance, where the body needs more insulin than usual to control blood sugar, is common in PMOS and is linked to hirsutism.[2]
In May 2026, PCOS was officially renamed polyendocrine metabolic ovarian syndrome (PMOS) after a global consensus process published in The Lancet. The new name reflects that the condition affects several hormone systems and metabolism, not just the ovaries. The change is being phased in.[5] Read more about how hirsutism and PMOS differ.
Idiopathic hirsutism and idiopathic hyperandrogenism
“Idiopathic” means no clear underlying cause is found. Together, these two groups made up almost a quarter of patients in the Palermo study.[3] The Endocrine Society defines idiopathic hirsutism as hirsutism with normal androgen levels and no other signs of a hormone disorder. It accounts for 5-20% of hirsute women, and about half of women with mild hirsutism.[1] It is a diagnosis of exclusion: your doctor first checks that your cycles are regular and your hormone tests are normal.
Non-classic congenital adrenal hyperplasia (NCAH)
NCAH is an inherited condition in which the adrenal glands lack enough of an enzyme called 21-hydroxylase and make extra androgens. It is passed on in an autosomal recessive way, which means you need a gene change from both parents. It affects about 1 in 1,000 people of European descent. It is much more common in some groups, for example about 1 in 27 Ashkenazi Jewish people and 1 in 53 Hispanic people.[6] It can look very similar to PMOS. The screening test is an early-morning blood test for 17-hydroxyprogesterone.[1]
Medications and other rare causes
Medications
Some medicines can cause hirsutism. The Endocrine Society names testosterone and other anabolic or androgenic steroids, and the epilepsy medicine valproic acid. It also flags a less obvious source: a partner’s testosterone gel, which can transfer through skin contact.[1] The NHS also lists some epilepsy medicines and steroids.[7] If your hair growth started after a new medicine, tell your doctor, but don’t stop a prescribed medicine on your own. Read more in drugs that can cause hirsutism.
Other hormone conditions (rare)
Cushing’s syndrome, where the body makes too much cortisol, and acromegaly, where it makes too much growth hormone, can occasionally cause hirsutism.[7] Doctors also check for thyroid problems and diabetes as part of the work-up.[8] See hirsutism and Cushing’s syndrome.
Is hirsutism hereditary?
Often, yes. Hirsutism runs strongly in families. Both the hormone conditions behind it and the factors that control follicle sensitivity, such as androgen receptor and 5α-reductase activity, have a substantial genetic component.[8] DermNet notes that hirsutism is usually genetic, often with both male and female relatives who have more hair than average.[9]
What family studies show
Most of the research looks at PMOS, the most common cause of hirsutism:
- In a US study of 93 women with PCOS, 24% of their mothers and 32% of their sisters also had PCOS, compared with an estimated 4% in the general population.[10]
- In another US study of 115 sisters of women with PCOS, 22% had PCOS themselves and another 24% had raised androgen levels with regular periods.[11]
- A Dutch study of more than 3,000 twins and sisters estimated that genes explain roughly 70-80% of the differences in who develops PCOS.[12]
These are small to mid-sized studies of PMOS, not of hirsutism itself, so they can’t tell you your personal risk. But they show that if your mother or sister has hirsutism or PMOS, your chance of developing it is higher than average.
Ethnicity and body hair
Normal amounts of body hair vary a lot between ethnic groups. Hirsutism appears to be less common in women of East Asian descent.[2] This is why the Endocrine Society uses different mFG score cutoffs for different groups, from about 2 in some Asian populations to 9-10 in Mediterranean, Hispanic and Middle Eastern women.[1] Having more body hair than your friends of a different background is not automatically a sign of a hormone problem. Our guide to the Ferriman-Gallwey score explains the cutoffs.
What this means for you
If hirsutism runs in your family, it’s still worth getting checked rather than assuming it’s “just genetic”. PMOS and NCAH both run in families and both have specific treatments. NCAH is relevant for family planning, because it can be passed to children, and genetic counseling may be offered.[2]
When to see a doctor quickly
Most hirsutism develops slowly, often starting around puberty. See a doctor soon if:[1], [7]
- The hair growth started suddenly or is getting worse within months
- You notice signs of virilization, such as a deepening voice, an enlarged clitoris or increased muscle mass
- Hair growth keeps getting worse despite treatment
These can be signs of an androgen-secreting tumor. Such tumors are found in about 0.2% of women with androgen excess, but more than half are cancerous, so they need prompt investigation.[1] Irregular or missing periods are also worth raising with a doctor, as they often point to PMOS.[7] Read more about virilization.
How the cause is found
The Endocrine Society recommends a blood test for total testosterone in women with an abnormal hirsutism score. Further tests depend on the results and your symptoms, for example 17-hydroxyprogesterone for NCAH. The guideline advises against routine blood tests for women with regular periods who only have a small area of unwanted hair and a normal score.[1] You can start by scoring yourself with the hirsutism self-check, then read which tests are used to diagnose hirsutism.
Frequently asked questions
What is the most common cause of hirsutism?
PMOS (formerly PCOS). It accounts for about 70-80% of cases.[1], [3]
Can you have hirsutism with normal hormone levels?
Yes. This is idiopathic hirsutism. It is thought to reflect hair follicles that are more sensitive to normal amounts of androgen.[1]
If my mother has hirsutism, will I get it?
Not necessarily, but your chances are higher. In family studies, about a quarter to a third of mothers and sisters of women with PCOS also had it.[10], [11]
Can stress cause hirsutism?
We found no good evidence that stress on its own causes hirsutism. If you notice new hair growth, it’s more useful to check for PMOS, medicines and other hormone causes.
Key takeaways
- Hirsutism results from androgens acting on sensitive hair follicles.
- PMOS (formerly PCOS) is by far the most common cause, at about 70-80% of cases.
- Around 1 in 4 women seen in specialist clinics have normal hormones or no identifiable cause.
- Hirsutism and PMOS run in families, and normal body hair varies between ethnic groups.
- Sudden or rapidly worsening hair growth, or signs of virilization, need prompt medical attention.
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Sources
- Martin KA, Anderson RR, Chang RJ, et al. Evaluation and Treatment of Hirsutism in Premenopausal Women: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(4):1233-1257. PubMed 29522147
- Escobar-Morreale HF, Carmina E, Dewailly D, et al. Epidemiology, diagnosis and management of hirsutism: a consensus statement by the Androgen Excess and Polycystic Ovary Syndrome Society. Hum Reprod Update. 2012;18(2):146-170. PubMed 22064667
- Carmina E, Rosato F, Jannì A, Rizzo M, Longo RA. Extensive clinical experience: relative prevalence of different androgen excess disorders in 950 women referred because of clinical hyperandrogenism. J Clin Endocrinol Metab. 2006;91(1):2-6. PubMed 16263820
- Teede HJ, Mousa A, Tay CT, et al. Summary of the 2023 international evidence-based guideline for the assessment and management of polycystic ovary syndrome: an Australian perspective. Med J Aust. 2024;221(7). Link
- Teede HJ, Bahri Khomami M, Morman R, et al. Polyendocrine metabolic ovarian syndrome, the new name for polycystic ovary syndrome: a multistep global consensus process. Lancet. 2026;407(10545):2329-2339. PubMed 42119588
- Livadas S, Bothou C. Management of the female with non-classical congenital adrenal hyperplasia (NCCAH): a patient-oriented approach. Front Endocrinol. 2019;10:366. Link
- NHS. Excessive hair growth (hirsutism). Accessed October 2026. Link
- Azziz R. The evaluation and management of hirsutism. Obstet Gynecol. 2003;101(5 Pt 1):995-1007. PubMed 12738163
- DermNet. Hirsutism: excessive hair in females. Accessed October 2026. Link
- Kahsar-Miller MD, Nixon C, Boots LR, Go RC, Azziz R. Prevalence of polycystic ovary syndrome (PCOS) in first-degree relatives of patients with PCOS. Fertil Steril. 2001;75(1):53-58. PubMed 11163816
- Legro RS, Driscoll D, Strauss JF 3rd, Fox J, Dunaif A. Evidence for a genetic basis for hyperandrogenemia in polycystic ovary syndrome. Proc Natl Acad Sci U S A. 1998;95(25):14956-14960. PubMed 9843997
- Vink JM, Sadrzadeh S, Lambalk CB, Boomsma DI. Heritability of polycystic ovary syndrome in a Dutch twin-family study. J Clin Endocrinol Metab. 2006;91(6):2100-2104. Link
This article is for education and is not medical advice. Talk to a doctor about diagnosis and treatment.