Dermatology� August 8, 2026� 8 min read

Hair Loss Causes: Why It Happens and What Actually Works

Medically Reviewed by Dr. Mark Stevens, Dermatology, Stanford Medicine on August 8, 2026. Adheres to strict medical communication criteria.

Dr. Hannah Lee, MD, FAAD

Dermatologist, NYU Langone at Premedice Systems

Summary & Key Takeaway

Hair loss (alopecia) is the thinning or shedding of hair from the scalp or body, affecting over 80 million Americans and triggered by genetics, hormones, medical conditions, medications, stress, or nutritional deficiencies. Losing 50�100 hairs per day is normal. But when you notice thinning patches, a widening part, or clumps of hair falling out, it's natural to worry. The emotional impact is significant � studies show that hair loss causes anxiety, depression, and reduced quality of life comparable to other chronic skin conditions. The good news: most forms of hair loss are treatable, and effective options have expanded significantly in recent years. The key is identifying the cause, because the treatment depends entirely on why you're losing hair. [Premedice](/) can help you evaluate your symptoms and determine whether medical evaluation is warranted.

?? Core Insights

Androgenetic alopecia (pattern hair loss) is the most common cause, affecting 50% of men by age 50 and 25% of women by age 60 � it's genetic and hormonal, not caused by shampoo or hat-wearing
FDA-approved treatments for pattern hair loss include minoxidil (topical, available over-the-counter) and finasteride (oral, prescription) � both are effective but require ongoing use to maintain results
Sudden, patchy hair loss (alopecia areata) is an autoimmune condition affecting 2% of the population � treatments include corticosteroid injections, JAK inhibitors (baricitinib), and topical immunotherapy
Reversible causes of diffuse hair loss include thyroid disease, iron deficiency, vitamin D deficiency, crash dieting, major surgery, childbirth, and certain medications � addressing the underlying cause restores growth
Newer treatments like low-level laser therapy, platelet-rich plasma (PRP) injections, and JAK inhibitors have expanded options beyond traditional minoxidil and finasteride. [Premedice](/) can help you identify the cause of your hair loss and determine the most appropriate treatment

Androgenetic Alopecia: The Most Common Cause

Androgenetic alopecia � pattern hair loss � is the most common form of hair loss, affecting approximately 50% of men and 25% of women by age 50. In men, it follows a predictable pattern: receding hairline (forming an 'M' shape), thinning at the crown, and progressive merging of the two areas. In women, it typically presents as diffuse thinning along the part line (a widening part) with preservation of the frontal hairline. The cause is genetic sensitivity of hair follicles to dihydrotestosterone (DHT), a hormone derived from testosterone. DHT miniaturizes hair follicles over successive growth cycles, producing progressively thinner, shorter hairs until the follicle stops producing visible hair.

Androgenetic alopecia is progressive � without treatment, it worsens over time. However, it's highly treatable when caught early. Minoxidil (Rogaine) is a topical solution (2% or 5%) applied twice daily that prolongs the growth phase of hair follicles and stimulates miniaturized follicles. It's available over-the-counter and works in about 60% of users, with results visible after 4�6 months. Finasteride (Propecia) is an oral prescription medication that blocks the conversion of testosterone to DHT, reducing DHT levels by about 70%. It's more effective than minoxidil in men, particularly for frontal hair loss, and works in about 80% of men. Women of childbearing age should not take finasteride due to birth defect risk.

Reversible Causes: When Hair Loss Signals Something Else

Diffuse hair loss � thinning all over the scalp rather than in a pattern � can signal underlying medical conditions that are treatable. Thyroid disease (both hyperthyroidism and hypothyroidism) is a common cause; treating the thyroid disorder typically restores hair growth within 6�12 months. Iron deficiency anemia, even without anemia (just low ferritin), can cause significant hair shedding � ferritin levels below 40 ng/mL are associated with hair loss in many people. Vitamin D deficiency, zinc deficiency, and protein malnutrition are also reversible causes.

Telogen effluvium is a temporary form of diffuse hair loss triggered by a major physiological stressor: childbirth (postpartum hair loss), major surgery, severe illness (including COVID-19), crash dieting, rapid weight loss, or emotional trauma. It occurs 2�4 months after the triggering event and typically resolves within 6�12 months. Certain medications � including beta-blockers, retinoids, anticoagulants, anticonvulsants, and some antidepressants � can cause hair loss as a side effect. If you notice sudden, diffuse shedding, a medical evaluation (blood tests for thyroid, ferritin, vitamin D, CBC, and metabolic panel) can identify reversible causes.

Alopecia Areata: Autoimmune Hair Loss

Alopecia areata is an autoimmune condition in which the immune system attacks hair follicles, causing smooth, round patches of complete hair loss. It affects about 2% of the population and can occur at any age. In most cases, it begins suddenly and can be triggered by stress, illness, or environmental factors in genetically predisposed individuals. The hair follicles are not destroyed � they're in a?? state and can regrow when the immune attack is suppressed. About 50% of people with a single patch experience spontaneous regrowth within a year.

Treatment options have improved significantly. For small patches, corticosteroid injections into the scalp (triamcinolone acetonide) are first-line, with regrowth in 60�80% of treated areas within 3�6 months. For more extensive disease, topical immunotherapy (squaric acid dibutylester, diphenylcyclopropenone) can stimulate regrowth by creating a controlled allergic reaction. The most significant advance is JAK inhibitors � oral medications (baricitinib/Olumiant, recently approved by the FDA for severe alopecia areata) that block the immune pathway attacking hair follicles. Clinical trials showed that 35�40% of patients achieved 80% or more scalp hair regrowth with JAK inhibitors. These represent the first targeted therapy for alopecia areata.

Newer Treatments: PRP, Laser, and Beyond

Low-level laser therapy (LLLT) uses red light to stimulate cellular metabolism in hair follicles, promoting growth. FDA-cleared laser devices (caps, combs, headbands) have shown modest but consistent benefits in clinical trials � about 20�30% improvement in hair density over 6 months. It's most effective for early-to-moderate androgenetic alopecia and is often used as an adjunct to minoxidil or finasteride. LLLT is safe, painless, and has no systemic side effects.

Platelet-rich plasma (PRP) involves drawing your blood, concentrating the platelets (which contain growth factors), and injecting it into the scalp. Multiple studies show PRP increases hair density and thickness in androgenetic alopecia, with results comparable to or better than minoxidil. Typically, 3�4 treatments are performed monthly, followed by maintenance treatments every 6�12 months. PRP is most effective for early-to-moderate hair loss and is considered an adjunct therapy rather than a standalone treatment. Emerging treatments include topical JAK inhibitors, exosome therapy, and stem cell-based approaches � these are promising but still in early clinical investigation.

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About the Author

Dr. Hannah Lee, MD, FAAD

Dr. Lee is a board-certified dermatologist specializing in hair disorders and medical dermatology.

Expert Takeaway

Hair loss has many causes, and treatment depends entirely on the diagnosis. Pattern hair loss responds to minoxidil, finasteride, and newer treatments. Sudden or patchy loss requires medical evaluation. Diffuse shedding often has reversible causes like thyroid disease or nutritional deficiency.

QFrequently Asked Questions

Q1Will I go completely bald?

Not necessarily. Androgenetic alopecia varies widely in severity � some men develop only mild recession, while others lose most scalp hair. Genetics determine both the pattern and severity. Starting treatment early (when thinning first becomes noticeable) produces the best results and can significantly slow or halt progression. Complete baldness is not inevitable for most people with pattern hair loss.

Q2Do hair growth supplements work?

Most hair growth supplements have limited evidence. Biotin only helps if you have a true deficiency (rare). The best approach is correcting documented deficiencies � iron, vitamin D, zinc, or protein. Excessive biotin can interfere with lab tests, so inform your doctor.

Q3How long before minoxidil or finasteride work?

Minoxidil takes 4�6 months for visible improvement and 12 months for full effect. Initial shedding in the first 2�4 months is normal and indicates it's working. Finasteride takes 6�12 months. Both require indefinite use � hair loss resumes within months of stopping.

Q4Is hair loss related to testosterone levels?

Not directly. Pattern hair loss is caused by follicle sensitivity to DHT, not total testosterone levels. Men with normal testosterone can have pattern hair loss if their follicles are DHT-sensitive. Blood testosterone levels are not useful for diagnosing or managing pattern hair loss.

Q5Can AI help diagnose or track hair loss?

AI tools can help track hair loss progression through photo analysis, correlate shedding patterns with health data (medications, stress, nutrition), and provide personalized treatment recommendations based on your specific type and severity of hair loss. Premedice can help you evaluate your symptoms, review relevant lab results, and determine whether a dermatology referral or specific treatment is appropriate.