Short answer: Hormones shape your hair in two opposite ways. Androgens such as testosterone can turn fine, light body hair into coarse, dark hair on the face and body, while thinning hair on the scalp in women who are prone to it. Big hormone shifts, such as after childbirth, stopping the pill, menopause or thyroid problems, can also cause shedding or change how your hair feels. Many of these changes are temporary.
Maybe your chin hairs got darker in your twenties, your hair fell out in clumps a few months after having a baby, or your scalp hair feels thinner and drier than it used to. Hormones are behind many of these changes. Here is how the main ones work, which changes usually reverse on their own and when it is worth seeing a doctor.
How hair grows
Each hair grows from a follicle in a cycle: a growing phase, a short transition and a resting phase, after which the hair falls out and a new one starts. Follicles cycle independently of each other, so you shed a few hairs every day rather than all at once.[1] Losing about 50 to 100 hairs a day is normal.[3][6]
There are two main hair types on the body. Vellus hair is fine, short and usually light. Terminal hair is larger and more heavily pigmented, like the hair on your head, eyebrows and, in adults, the armpits and pubic area.[1] Hormones can change which type a follicle produces.
Androgens: the main hormones behind unwanted hair
Androgens are often called “male” hormones, but everyone makes them. In androgen-sensitive areas, such as the upper lip, chin, chest and stomach, androgens turn vellus follicles into terminal follicles, so fine hair becomes coarse and dark. Inside the follicle, an enzyme called 5-alpha reductase converts testosterone into dihydrotestosterone (DHT), a stronger androgen.[1] When this happens in a male-like pattern in women, it is called hirsutism.
How much hair grows depends on two things: How much androgen is in your blood, and how sensitive your follicles are. Sensitivity varies a lot between people, which is why some women with normal hormone levels still develop hirsutism.[1] Read more in what causes hirsutism and what causes excess testosterone in females.
Why androgens can thin scalp hair
On the scalp, the effect can be the opposite. In female pattern hair loss, follicles gradually shrink, so the hair grows back finer and the overall volume drops. Genes play a large role, and most affected women have normal androgen levels in their blood. The exact role of androgens and estrogen in women is still unclear.[2] Around 40% of women show some signs of hair loss by age 50.[2]
PMOS (formerly PCOS)
PMOS, previously called polycystic ovary syndrome (PCOS), is the condition most often behind raised androgens in women. It affects about 10% to 13% of women worldwide.[8] The name was changed in 2026 to reflect that it affects several hormone systems and metabolism.[9] PMOS can cause hirsutism, acne and scalp thinning, although not every woman gets all three. See hirsutism and acne and hair loss in PMOS.
Pregnancy and childbirth
Many women notice heavy shedding after having a baby. It usually starts about two months after the birth and peaks around four months. This is a form of telogen effluvium, a temporary increase in shedding, and it is normal.[3] MedlinePlus notes that hair loss after childbirth often improves within 6 months to 2 years.[4]
Starting or stopping the pill
Stopping birth control pills is a known trigger for temporary shedding.[3] Some birth control pills can also cause hair loss while you take them.[4] On the other hand, the combined pill is the first-line medication for hirsutism, because it can reduce unwanted hair growth over about six to nine months.[1] If your hair changed after starting or stopping a pill, mention it to your doctor.
Thyroid hormones
Your thyroid gland makes hormones that control your metabolism. An underactive thyroid (hypothyroidism) can cause thin, brittle hair and nails and dry skin early on, and thinning eyebrows later if it is not treated.[5] Thyroid disease is also a recognized cause of hair loss.[4] The good news is that hair loss from a medical condition usually stops or grows back once the condition is treated.[6] Read more in can the thyroid cause hirsutism?
Menopause and aging
As women age, hair tends to become thinner and less dense.[4] Hair loss around menopause often improves within 6 months to 2 years, according to MedlinePlus.[4] At the same time, some women notice more chin or upper lip hair after menopause. Our article on hirsutism and menopause explains why, and our guide to whether leg hair stops growing with age covers changes in body hair.
Other things that change your hair
Stress, illness and weight loss
High stress, a high fever, surgery, recovering from an illness and losing 20 pounds or more can all trigger temporary shedding. It usually stops by itself, and hair often regains its fullness within 6 to 9 months.[3]
Diet and nutrients
Iron deficiency is a common, temporary cause of hair loss.[6] Severe malnutrition, for example in anorexia nervosa, can cause the opposite: a growth of fine, soft hair on the body.[7] Many hair supplements are sold with big claims, but evidence is thin. The NIH Office of Dietary Supplements says claims that biotin improves hair are supported, at best, by a few case reports and small studies, and that biotin deficiency is rare.[10] High-dose biotin can also distort thyroid and other hormone test results.[10]
Medications
Several common medicines are linked to hair loss, including retinoids, some birth control pills, beta-blockers, calcium channel blockers, certain antidepressants and NSAID painkillers such as ibuprofen.[4] Other drugs can increase body hair, including minoxidil, ciclosporin, phenytoin and anabolic steroids.[7] Never stop a prescribed medicine without talking to your doctor. See our list of drugs that can cause hirsutism.
Coloring, bleaching and styling
Harsh hair-care products and hairstyles that pull on the hair are listed by the American Academy of Dermatology as causes of hair loss.[3] If your hair feels different after coloring, bleaching or heat styling, gentler products, less heat and looser styles are low-risk changes worth trying.
When to see a doctor
See a doctor if you are worried about changes in your hair, or if hair loss is affecting how you feel.[6] See a doctor soon if you notice:
- New coarse, dark hair on your face, chest or stomach that appears suddenly or gets worse quickly
- A deepening voice, an enlarged clitoris or increased muscle mass, which are signs of virilization
- Irregular or missing periods
- Heavy shedding that lasts more than a few months, or bald patches
- Dry skin and brittle nails alongside thinning hair, which can point to a thyroid problem
Our hirsutism self-check can help you judge whether your body hair is within the usual range.
Frequently asked questions
Can hormones change your hair texture?
Yes. Androgens can make fine body hair coarse and dark, and an underactive thyroid can make hair thin and brittle.[1][5]
Which hormone causes facial hair in women?
Mainly androgens such as testosterone and its stronger form, DHT, acting on sensitive hair follicles.[1]
Does hair grow back after hormonal shedding?
Usually, yes. Shedding after childbirth, stress or stopping the pill is usually temporary.[3] Female pattern hair loss is different and often needs treatment.[2]
Why is my hair thinning but my facial hair getting thicker?
Androgens affect follicles differently depending on where they are. They can make facial hair coarser while shrinking scalp follicles in women who are genetically prone.[1][2]
Key takeaways
- Androgens turn fine body hair into coarse, dark hair in sensitive areas, which causes hirsutism.
- The same hormones can thin scalp hair in women who are prone to female pattern hair loss.
- Shedding after childbirth, stress or stopping the pill is common and usually temporary.
- Thyroid problems, low iron and some medicines can also change your hair.
- Sudden or rapidly worsening hair growth, or signs of virilization, need a prompt medical check.
Free: The Hirsutism Action Plan
A 12-page guide: what’s causing your hair growth, which tests to ask your doctor for, and which treatments actually work, plus a printable doctor visit checklist.
You’ll also get our weekly email. Unsubscribe anytime.
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
- DermNet. Female pattern hair loss. Accessed October 2026. Link
- American Academy of Dermatology. Do you have hair loss or hair shedding?. Accessed October 2026. Link
- MedlinePlus. Hair loss. Accessed October 2026. Link
- MedlinePlus. Hypothyroidism. Accessed October 2026. Link
- NHS. Hair loss. Accessed October 2026. Link
- DermNet. Hypertrichosis. Accessed October 2026. Link
- Teede HJ, Tay CT, Laven JJE, et al. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. J Clin Endocrinol Metab. 2023;108(10):2447-2469. PubMed 37580314
- 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
- NIH Office of Dietary Supplements. Biotin: Fact Sheet for Health Professionals. Accessed October 2026. Link
This article is for education and is not medical advice. Talk to a doctor about diagnosis and treatment.