Short answer: Hirsutism and hypertrichosis both mean “too much hair,” but they are different conditions. Hirsutism is coarse, dark hair in a male pattern in women, driven by androgens (hormones such as testosterone). Hypertrichosis is excess hair anywhere on the body, in any sex or age, that is not caused by androgens.[1][2][3] “Werewolf syndrome” is a nickname for the rare, inborn forms of hypertrichosis.
If you have more hair than you would like, the word you see online matters, because it points to different causes and different next steps. Hirsutism is common and usually linked to hormones. Hypertrichosis is much less common and has a long list of possible causes, from medicines to rare genetic conditions.[2][3] This article explains how to tell them apart, what causes each, and what the facts are behind the “werewolf syndrome” headlines.
Hirsutism vs. hypertrichosis: the key differences
The main difference is where the hair grows and why. Hirsutism is defined as excessive terminal hair (thick, pigmented hair) that appears in a male pattern in women.[3] It shows up in androgen-sensitive areas such as the upper lip, chin, chest, stomach, lower back and inner thighs. In these areas, androgens turn fine, light vellus hair into coarse terminal hair.[3][4]
Hypertrichosis is hair growth beyond what is normal for a person’s age, sex and ethnic background.[1][2] It is not limited to women or to a male pattern, and it often affects areas that do not depend on androgens, such as the forehead, arms or back of a child.[1][2]
| Hirsutism | Hypertrichosis | |
|---|---|---|
| Who it affects | Women (the term is used for women) | Anyone: women, men, children, babies |
| Where the hair grows | Male-pattern areas: face, chest, stomach, back, thighs | Anywhere, either all over the body or in one patch |
| Main driver | Androgens, or follicles that are extra sensitive to them | Not androgens: genes, medicines, illness, local skin factors |
| How common | Common | Uncommon; inborn forms are very rare |
| Typical cause | PMOS (formerly PCOS) | Medicines, malnutrition, other illnesses, rare genetic conditions |
If you are not sure which one describes you, our hirsutism self-check walks you through the hair pattern doctors look at, and the Ferriman-Gallwey score explains how hirsutism is measured.
What causes hirsutism?
Hirsutism happens when androgen levels are higher than usual, or when hair follicles react more strongly to normal levels.[5] The most common cause is PMOS, previously called polycystic ovary syndrome (PCOS).[5] PCOS was officially renamed polyendocrine metabolic ovarian syndrome (PMOS) in 2026 after a global consensus process published in The Lancet.[6]
Other, less common causes include certain medicines (including some epilepsy medicines and steroids), Cushing’s syndrome, acromegaly and, rarely, a tumor that makes hormones.[5] Sometimes no clear cause is found.[5] A tendency to more body and facial hair also runs in families.[4] For the full picture, read what causes hirsutism.
What causes hypertrichosis?
Doctors sort hypertrichosis by when it starts (congenital, meaning present at birth, or acquired later in life) and how much skin it covers (generalized, meaning widespread, or localized, meaning one area).[2] The acquired type is far more common than the congenital type.[2]
Acquired hypertrichosis (develops later in life)
Known causes of widespread hair growth later in life include:[1][2]
- Medicines: ciclosporin (an immune-suppressing drug), phenytoin (an epilepsy drug), androgenic steroids and minoxidil.[1] Other drugs, such as corticosteroids and interferon, have also been linked to it.[2]
- Malnutrition, including from anorexia nervosa.[1][2]
- Porphyria cutanea tarda, a disorder of how the body makes heme (part of red blood cells).[1]
- Other conditions, such as hypothyroidism (an underactive thyroid) and juvenile dermatomyositis, an inflammatory disease of the skin and muscles in children.[2]
- Cancer. A rare form called acquired hypertrichosis lanuginosa, sometimes called “malignant down,” causes fine, soft hair, usually on the face, and is often linked to a cancer diagnosis. Doctors don’t know why cancer triggers it.[1]
Localized hypertrichosis (a single patch)
Hair can also thicken in one area only. DermNet lists these causes:[1]
- More blood flow to one area of skin
- Repeated rubbing or scratching, for example with lichen simplex, a chronic itchy skin condition
- Wearing a plaster cast for a while
- Repeated use of minoxidil, strong steroid creams, iodine or a light treatment called PUVA on that area
- Long eyelashes caused by some medicines, such as bimatoprost eye drops
Some birthmarks are hairy too. A Becker nevus, for example, is a large brown patch, usually on the shoulder or upper chest, that often becomes darker and hairy after puberty. It is about five times more common in males and is considered harmless.[7]
Congenital hypertrichosis (present from birth)
These are the forms behind the “werewolf syndrome” nickname. They are believed to be genetic, either inherited or caused by a new gene change.[1]
- Congenital hypertrichosis lanuginosa: The fine baby hair (lanugo) that is usually shed before birth stays and keeps growing. DermNet describes it as “a very rare syndrome with only about 50 cases reported worldwide since the Middle Ages.”[1]
- Congenital hypertrichosis terminalis: Thick, dark hair grows over the whole body. It is almost always linked to gingival hyperplasia, an overgrowth of the gums.[1]
- Nevoid hypertrichosis: A single, well-defined patch of thick hair, such as one very bushy eyebrow. A tuft of hair over the lower back can be a sign of spina bifida, so it should be checked by a doctor.[1]
Congenital hypertrichosis can also be one feature of a wider genetic syndrome, so a baby with widespread hair from birth is usually assessed for other conditions.[2] Read more in hirsutism in babies, toddlers and kids.
Werewolf syndrome: facts and fiction
“Werewolf syndrome” is not a medical term. It is a popular nickname for the rare congenital forms of hypertrichosis, especially when hair covers the face and body.[1] The condition is real, but the people who have it are not “half animal.” They simply have hair follicles that keep producing hair where most people’s don’t.
Is werewolf syndrome genetic?
Often, yes. In 2011, researchers studied a five-generation Chinese family with 11 affected members who had widespread hair from birth, along with a previously reported Mexican family.[8] In both families, a piece of DNA from another chromosome had been inserted into the X chromosome at the same spot, close to a gene called SOX3. The insertions were found in affected family members and not in 1,274 people without the condition.[8]
The researchers think the extra DNA may switch on SOX3 in hair follicles, but they could not prove it, because they did not detect SOX3 activity in the follicles they tested.[8] So the gene link is a strong lead, not a settled explanation. The study also does not tell us anything about treating hirsutism or baldness.
Is there a cure?
There is no cure for the inborn forms. For acquired hypertrichosis, treating the cause, such as stopping a medicine with your doctor’s agreement or treating malnutrition, may help.[1] Otherwise, treatment for both conditions is hair removal.[1]
How is excess hair treated?
The approach depends on the cause. For hirsutism, doctors look for and treat hormonal causes, and may offer the combined pill, anti-androgen medicines or a prescription cream for facial hair (eflornithine).[3][5] See hirsutism medication for details. For hypertrichosis, hormone treatment does not help, because androgens are not the cause.[1][2]
Temporary hair removal
Shaving, waxing, plucking, hair removal creams and bleaching are the at-home options the NHS lists.[5] They work immediately but have to be repeated, and they can cause skin irritation, allergic reactions or scarring.[1] Shaving does not make hair grow back thicker. It only looks coarser because the cut tip is blunt.[9] These are practical tools rather than medical treatments, so there are no trials comparing them for hypertrichosis.
Laser hair removal and IPL
Evidence: Strong Laser hair removal is recommended in the Endocrine Society hirsutism guideline for women with brown, auburn or black hair.[3] DermNet notes that it seems to have fewer side effects and longer-lasting results than older methods.[1] Results are not permanent and vary from person to person, and treatment is usually not available on the NHS.[5] Women of Mediterranean or Middle Eastern background treated on the face have a higher risk of paradoxical hypertrichosis, meaning more hair growth near the treated area.[3] Read our guide to laser, IPL and electrolysis.
Electrolysis
Evidence: Moderate Electrolysis destroys hair follicles one by one with an electric current. The Endocrine Society suggests it for white or blonde hair, which lasers cannot target well.[3] It treats one follicle at a time and, like laser, can be expensive.[5]
When to see a doctor
See a doctor if you are not sure what kind of hair growth you have, and soon if:[3][5]
- New thick, dark hair starts suddenly or gets worse within months
- Your voice gets deeper, your muscles get bigger, or your clitoris gets larger (signs of virilization)
- Your periods become irregular or stop
- Fine, soft hair suddenly appears on your face or body as an adult[1]
- Hair growth started after a new medicine
- A baby has a tuft of hair over the lower back
Sudden, fast hair growth with signs of virilization can point to a hormone-producing tumor, which is rare but needs quick testing.[3] Learn more about virilization.
Frequently asked questions
Is hirsutism a type of hypertrichosis?
Not quite. Both mean extra hair, but doctors use “hirsutism” for androgen-driven, male-pattern hair in women, and “hypertrichosis” for extra hair that is not caused by androgens.[2][3]
Is werewolf syndrome real?
Yes, in the sense that congenital hypertrichosis exists. It is extremely rare: congenital hypertrichosis lanuginosa has only about 50 reported cases worldwide since the Middle Ages.[1] “Werewolf syndrome” is just a nickname.
Can medication cause hypertrichosis?
Yes. Ciclosporin, phenytoin, minoxidil and androgenic steroids are known causes.[1] Don’t stop a prescribed medicine on your own. Talk to your doctor about alternatives.
Can men have hypertrichosis?
Yes. Unlike hirsutism, hypertrichosis affects any sex and age.[1] Read more in excessive body hair in men.
How do I know if I have hirsutism or hypertrichosis?
Look at the pattern. Coarse, dark hair on the face, chest, stomach or back, especially with acne or irregular periods, points to hirsutism. Hair in unusual places, all over, or in one patch points to hypertrichosis. A doctor can confirm it with an exam and, if needed, blood tests.[1][3]
Key takeaways
- Hirsutism is androgen-driven, male-pattern hair growth in women. Hypertrichosis is extra hair anywhere, in anyone, that is not caused by androgens.
- The most common cause of hirsutism is PMOS (formerly PCOS). Acquired hypertrichosis is usually caused by medicines, malnutrition or another illness.
- “Werewolf syndrome” refers to inborn hypertrichosis, which is extremely rare and often genetic.
- Hair removal works for both. Hormone treatment helps hirsutism but not hypertrichosis.
- Sudden hair growth, virilization or new fine hair on the face as an adult needs a prompt medical check.
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Sources
- DermNet. Hypertrichosis. Accessed October 2026. Link
- Pavone P, Praticò AD, Falsaperla R, et al. Congenital generalized hypertrichosis: the skin as a clue to complex malformation syndromes. Ital J Pediatr. 2015;41:55. PubMed 26242548
- 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
- DermNet. Hirsutism. Accessed October 2026. Link
- NHS. Hirsutism. Accessed October 2026. Link
- Teede HJ, et al. Polyendocrine metabolic ovarian syndrome, the new name for polycystic ovary syndrome: a multistep global consensus process. Lancet. 2026;407(10545):2329-2339. Published online May 12, 2026. PubMed 42119588
- DermNet. Becker naevus. Accessed October 2026. Link
- Zhu H, Shang D, Sun M, et al. X-linked congenital hypertrichosis syndrome is associated with interchromosomal insertions mediated by a human-specific palindrome near SOX3. Am J Hum Genet. 2011;88(6):819-826. PubMed 21636067
- DermNet. Shaving. Accessed October 2026. Link
This article is for education and is not medical advice. Talk to a doctor about diagnosis and treatment.