Hair Loss in Men and Women: Medical Causes, Diagnosis, and Treatment Options

Hair loss is one of the most common concerns I evaluate in dermatology practice, and it is also one of the most emotionally charged. Nearly every patient who comes in for hair loss has already spent months trying to diagnose themselves with varying degrees of accuracy. The most important thing I tell them early is that hair loss is not one condition — it is a symptom with many causes, and the treatment approach differs entirely depending on which cause is driving it. Treating androgenetic alopecia the same way you treat telogen effluvium fails. Treating alopecia areata like iron deficiency anemia fails. Getting this right starts with a careful history, examination, and often bloodwork — not with grabbing the first product from a pharmacy shelf.

Normal Hair Growth: A Baseline for Understanding Loss

Normal scalp hair grows in cycles. The anagen (growth) phase lasts 2–7 years, during which the follicle actively produces a hair strand. This is followed by a brief catagen (transition) phase of 2–3 weeks, then a telogen (resting) phase of approximately 3 months, after which the hair is shed and a new anagen cycle begins. The scalp contains approximately 100,000 follicles, and at any given time about 85–90% are in anagen and 10–15% are in telogen. Losing 50 to 100 hairs per day is entirely normal — it is the visible consequence of follicles transitioning from telogen to the new anagen phase.

Noticeable hair loss occurs when this balance is disrupted: either follicles are permanently miniaturizing (androgenetic alopecia), an abnormally large percentage is pushed into telogen simultaneously (telogen effluvium), follicles are attacked by the immune system (alopecia areata), or the follicle is physically or structurally damaged (scarring alopecias).

Androgenetic Alopecia: The Most Common Type in Both Sexes

Androgenetic alopecia (AGA) is the most prevalent cause of hair loss, affecting approximately 50% of men by age 50 and 40–50% of women by age 50. It is a genetically driven, hormonally mediated process in which scalp follicles are progressively miniaturized by dihydrotestosterone (DHT), a potent androgen derived from testosterone via the enzyme 5-alpha reductase. Miniaturized follicles produce progressively shorter, finer, less pigmented hairs until they eventually become dormant.

Male Pattern Hair Loss

In men, AGA follows the Norwood-Hamilton scale, which classifies progression from Type I (minimal frontotemporal recession) through Type VII (only a horseshoe fringe of hair remaining at the sides and back). The pattern typically begins at the temples and crown. The sides and back of the scalp retain their hair because those follicles are DHT-resistant — this is why hair transplants work and why donor hair is harvested from these zones.

Female Pattern Hair Loss

In women, AGA presents differently and is classified by the Ludwig scale (I–III). Women typically experience diffuse thinning over the central and crown area while the frontal hairline is relatively preserved — a pattern described as a "Christmas tree" on parting. Complete baldness as seen in men is uncommon. AGA in women can begin as early as the twenties or thirties, and accelerates at menopause when estrogen's partial protective effect on follicles diminishes. In premenopausal women with AGA, androgen levels are often normal — the follicles are simply more sensitive to circulating DHT.

Telogen Effluvium: The Shedding After a Shock

Telogen effluvium (TE) is characterized by diffuse hair shedding — handfuls in the shower, clumps on the pillow — occurring 2 to 4 months after a triggering event that shocked a large proportion of follicles into the telogen (resting) phase simultaneously. The lag time is characteristic and clinically important: patients experiencing TE after a major illness in February will notice shedding in April or May and may not connect the two.

Common triggers include: major surgery or general anesthesia, childbirth (postpartum telogen effluvium is extremely common and typically begins 2–4 months after delivery), significant physical or emotional stress, rapid or extreme weight loss (crash dieting), high fever or severe acute illness (COVID-19 is now among the most common triggers), hypothyroidism or hyperthyroidism, and nutritional deficiencies — particularly iron and protein.

Telogen effluvium is typically self-limiting. Once the trigger resolves, follicles return to anagen and shedding normalizes over 3 to 6 months, with full density regained by 6 to 12 months in most cases. Chronic telogen effluvium — lasting more than 6 months — is less common, often has a persistent triggering factor, and warrants comprehensive blood work to identify correctable causes.

Alopecia Areata: When the Immune System Attacks Hair Follicles

Alopecia areata (AA) is an autoimmune condition in which T-lymphocytes attack the hair follicle, disrupting the anagen phase and producing characteristic non-scarring patchy hair loss. The classic presentation is one or more smooth, round or oval patches of complete hair loss on the scalp, ranging from a few centimeters to much larger. Exclamation mark hairs — short hairs that taper at the base — at the edge of a patch are a characteristic finding on examination.

AA can progress to alopecia totalis (complete scalp hair loss) or alopecia universalis (complete body hair loss) in a minority of patients. It is associated with other autoimmune conditions including thyroid disease, vitiligo, and type 1 diabetes. The lifetime prevalence is approximately 2% of the population.

First-line treatment for limited patches is intralesional corticosteroid injections, which stimulate regrowth in responsive patients. For extensive or refractory AA, JAK inhibitors — particularly baricitinib (Olumiant) and ritlecitinib (Litfulo), both recently FDA-approved for AA — represent a significant advance, with ritlecitinib approved specifically for patients 12 and older with severe AA. They block the inflammatory signaling pathway that drives follicular attack and have shown regrowth rates substantially higher than prior treatments.

Thyroid-Related Hair Loss

Both hypothyroidism and hyperthyroidism can cause diffuse hair thinning and shedding. Thyroid hormone regulates the hair growth cycle, and dysfunction in either direction disrupts it. Hypothyroid hair loss tends to be diffuse thinning with a dull, dry texture; the outer third of the eyebrows is a classical but inconsistent finding. Hyperthyroid hair loss tends to produce a finer, more brittle texture.

Thyroid-related hair loss is largely reversible once the thyroid condition is effectively treated and hormone levels normalized — though improvement typically takes 6 to 12 months after achieving euthyroid status. A TSH is the appropriate initial screening test and should be included in the workup of any patient with unexplained diffuse hair loss.

Iron Deficiency and Hair Loss

Iron deficiency is the most common nutritional cause of hair loss, particularly in premenopausal women with heavy menstrual periods, vegetarians, and people with malabsorptive GI conditions. Ferritin, the iron storage protein, is the most sensitive marker. While the exact threshold is debated, most dermatologists target a ferritin level of 40 ng/mL or above for optimal hair growth, and levels below 30 ng/mL are associated with telogen effluvium even in the absence of frank anemia.

Iron deficiency hair loss presents as diffuse shedding, similar to telogen effluvium. Treatment with iron supplementation (typically ferrous sulfate 325 mg once or twice daily with vitamin C to enhance absorption, taken away from food and calcium) generally produces noticeable improvement in 3 to 6 months once ferritin levels are restored. A full blood count and ferritin level should be standard in the hair loss workup.

Treatment Options

Minoxidil

Minoxidil is FDA-approved for both male and female pattern hair loss and is available over the counter in 2% and 5% topical solutions and foam. It prolongs the anagen phase and increases follicular blood supply. Typical results: 20–40% of users experience meaningful regrowth, and a larger proportion experience stabilization. The 5% foam formulation is now preferred for women due to better cosmetic acceptability and equivalent or better efficacy than 2% solution. Oral low-dose minoxidil (2.5 mg daily for women, 2.5–5 mg for men) has emerged as a clinically effective alternative with growing evidence, now widely used off-label. Side effects include initial shedding during the first 4–6 weeks (alarming but temporary), and with topical use, possible facial hair growth in some women. Minoxidil must be continued indefinitely — cessation leads to return of loss within 3 to 6 months.

Finasteride (Men)

Finasteride 1 mg daily (Propecia) is an oral 5-alpha reductase inhibitor that blocks the conversion of testosterone to DHT, reducing DHT levels in the scalp by approximately 60%. It is FDA-approved for male pattern hair loss and is highly effective: clinical trials show 83% of men maintained hair count versus placebo, and approximately 66% experienced visible regrowth at two years. It must be taken continuously — stopping leads to reversal within 12 months. Side effects include sexual dysfunction (decreased libido, erectile dysfunction, ejaculatory disorder) in a small percentage (approximately 1.4–3.8% in trials), which is reversible in most cases upon stopping. Post-finasteride syndrome — a controversial persistent syndrome of sexual, neurological, and psychological side effects after stopping — is poorly characterized but has prompted FDA label updates.

Spironolactone (Women)

Spironolactone is an aldosterone antagonist with anti-androgen properties widely used off-label for female androgenetic alopecia, particularly in premenopausal women with hormonal features. It blocks androgen receptors in the hair follicle and reduces adrenal androgen production. Doses of 100–200 mg daily are typically used. Evidence from observational studies and small trials supports efficacy in female AGA. Side effects include menstrual irregularity, breast tenderness, and the requirement for contraception given teratogenic risk. Not appropriate during pregnancy. Potassium levels should be monitored, particularly in patients taking ACE inhibitors or ARBs.

Platelet-Rich Plasma (PRP)

PRP involves drawing the patient's blood, centrifuging it to concentrate platelets and growth factors, and injecting the concentrate into the scalp. The growth factors — including platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) — are thought to stimulate follicular activity. Evidence from randomized controlled trials is encouraging for AGA and alopecia areata, though methodological variation across studies limits definitive conclusions. PRP is generally considered a useful adjunct, particularly for patients who cannot use or have not responded adequately to first-line treatments. Typical protocol is 3 monthly sessions followed by maintenance every 3–6 months.

Hair Transplant Surgery

Hair transplant surgery — predominantly follicular unit extraction (FUE) or follicular unit transplantation (FUT/strip) — is the only current option that provides permanent redistribution of DHT-resistant follicles from the donor area to thinning zones. Results are permanent and natural-appearing in skilled hands. Candidates must have sufficient donor hair, stable pattern loss, and realistic expectations. Cost ranges from $4,000 to $15,000 or more depending on the extent of coverage. Medical therapy (minoxidil and/or finasteride) should be continued after transplant to preserve non-transplanted native hairs from continued miniaturization.

When Hair Loss Reverses on Its Own

Telogen effluvium following a discrete trigger (childbirth, illness, crash dieting, surgery) is expected to self-resolve as the triggering factor resolves. Most patients recover full or near-full density within 6 to 12 months. Alopecia areata in its patchy form also frequently regrows spontaneously, though recurrence is common. Iron deficiency and thyroid-related hair loss are largely reversible with treatment of the underlying cause. Androgenetic alopecia does not reverse on its own — it is progressive and requires ongoing intervention to halt or partially reverse miniaturization.

When to See a Doctor

See a dermatologist or physician if you are shedding noticeably more than usual, notice widening part lines or decreased density, see patchy or irregular hair loss, or if hair loss is accompanied by other symptoms such as fatigue, weight changes, or irregular periods. Blood work including TSH, ferritin, complete blood count, and in women a hormonal panel can rule out reversible systemic causes quickly. Early intervention for androgenetic alopecia specifically matters — follicles that are miniaturizing but not yet dormant respond to treatment; follicles that are gone do not. JourneyDoctors connects you with trained specialists from $19. Start a consultation today — no waiting room, no referral needed.

This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment.

Frequently Asked Questions

Is hair loss from stress permanent?

No, in most cases. Stress-triggered telogen effluvium is reversible once the stressor resolves. Shedding peaks 2–4 months after the stressor and typically resolves over the following 3–6 months, with full regrowth by 6–12 months. However, sustained chronic stress that is not addressed can produce ongoing shedding or, in genetically predisposed individuals, accelerate underlying androgenetic alopecia, which is progressive.

Can you regrow hair once it's lost?

It depends on the cause. Telogen effluvium, alopecia areata (often), and hair loss from correctable causes like iron deficiency or hypothyroidism can fully regrow. Early-stage androgenetic alopecia — where follicles are miniaturizing but not yet dormant — can experience partial regrowth with minoxidil and/or finasteride/spironolactone. Late-stage AGA where follicles have become completely dormant generally does not respond to topical or oral treatments and requires hair transplant for cosmetic correction.

How do I know if my hair loss is hormonal?

Hormonal hair loss in women typically presents as central scalp thinning with preserved frontal hairline, often worsening around hormonal transitions such as stopping the pill, postpartum, perimenopause, or with PCOS-related androgen excess. Blood tests including testosterone, DHEA-S, and sex hormone-binding globulin (SHBG) can identify androgen excess, though most women with AGA have normal androgen levels. A dermatologist can assess the pattern and order appropriate tests.

Does wearing hats cause hair loss?

No. This is a persistent myth. Wearing hats does not cause follicular miniaturization, restrict blood flow sufficiently to damage follicles, or accelerate androgenetic alopecia. Extremely tight hairstyles worn consistently — such as tight braids, weaves, or ponytails — can cause traction alopecia, a form of hair loss from mechanical tension on the follicle. Traction alopecia is initially reversible if the tension is removed; if sustained for years, it can cause permanent follicular scarring.

Should I take biotin supplements for hair loss?

Biotin supplementation is appropriate only in documented biotin deficiency, which is rare in people with normal diets. In biotin-sufficient individuals — which describes most people — biotin supplements do not promote hair growth and do not treat any common cause of hair loss. They are however heavily marketed for this purpose. A meaningful caution: high-dose biotin supplementation interferes with multiple laboratory assays, producing falsely abnormal thyroid function, cardiac troponin, and hormone results. If you are taking biotin and having blood work, stop it for at least 48 hours beforehand.