Androgenetic alopecia is the most common non-scarring hair loss, characterized by progressive miniaturization of hair follicles in androgen-sensitive scalp regions. Men show bitemporal recession and vertex thinning (Hamilton–Norwood patterns); women show diffuse central thinning with preserved frontal hairline (Ludwig/Sinclair patterns). Dihydrotestosterone (DHT) acting on genetically susceptible follicles shortens anagen and miniaturizes follicles. Management is long-term and aims to slow loss and promote regrowth: topical minoxidil, oral finasteride/dutasteride (men), low-level laser therapy, antiandrogens in women, and hair transplantation for suitable candidates.
Epidemiology
- Affects up to 50% of men by age 50; prevalence increases with age in both sexes.
- Strong genetic component; polygenic inheritance.
Pathophysiology
- 5α-reductase converts testosterone to DHT, which binds androgen receptors in follicular dermal papilla of susceptible areas, shortening anagen and reducing shaft diameter.
- Microinflammation and altered perifollicular signaling may contribute.
Clinical Features and Classification
- Men: Hamilton–Norwood I–VII; “whorl” vertex and bitemporal recession.
- Women: Ludwig I–III or Sinclair 1–5; widened midline part with frontal hairline largely preserved; “Christmas tree” sign.
- Dermoscopy: hair shaft diameter diversity (>20%), peripilar signs, miniaturized hairs.
Differential Diagnosis
- Telogen effluvium (diffuse shedding), chronic telogen effluvium (women), alopecia areata incognita, traction alopecia, frontal fibrosing alopecia (receding frontal line with scarring), tinea capitis.
Workup
- Clinical diagnosis. Consider ferritin, TSH if diffuse shedding or symptoms; in women with signs of hyperandrogenism (hirsutism, acne, irregular menses), assess androgens (total/free testosterone, DHEAS, prolactin).
- Baseline photos and trichoscopy for monitoring.
Management
- Foundational counseling
- Early, continuous therapy is key; benefits plateau while on treatment and regress after stopping.
- Set realistic expectations: slowing loss is success; regrowth varies.
- Topical and oral hair growth promoters
- Minoxidil:
- Men: 5% solution/foam once or twice daily.
- Women: 5% once daily foam or 2% solution twice daily; 5% often more effective but may increase facial hypertrichosis.
- Initial shedding possible in 6–8 weeks; peak effect ~6–12 months; continue long-term.
- Oral minoxidil (off-label):
- Low-dose 0.625–2.5 mg/day; can be effective for both sexes; monitor BP, edema, tachycardia, hypertrichosis; avoid in pregnancy; coordinate with primary care for cardiovascular history.
- Antiandrogens and 5α-reductase inhibitors
- Men:
- Finasteride 1 mg/day (type II 5α-RI): improves hair count and slows loss; sexual adverse effects occur in a minority; discuss risks including rare persistent symptoms; teratogenic to male fetuses—handle tablets with care.
- Dutasteride 0.5 mg/day (type I/II 5α-RI) off-label; often more potent; similar side-effect profile.
- Women:
- Premenopausal: spironolactone 50–200 mg/day; contraception recommended; monitor potassium in at-risk patients; helps acne/hirsutism.
- Postmenopausal: finasteride 1–5 mg/day or dutasteride off-label may help; ensure no pregnancy potential; evidence strongest at higher doses with monitoring.
- Cyproterone acetate where available; consider risks (VTE, hepatic).
- Devices and procedures
- Low-level laser/light therapy (LLLT) caps/combs: modest benefit; needs ongoing use.
- Platelet-rich plasma (PRP): series of injections can improve density/shaft diameter; protocols vary; maintenance needed.
- Microneedling: adjunct to topicals; weekly/biweekly sessions shown to enhance minoxidil response.
- Hair transplantation:
- Follicular unit extraction (FUE) or strip FUT; ideal when donor area stable and expectations realistic.
- Women are candidates with stable AGA and adequate donor density; address diffuse thinning first.
- Adjuncts and lifestyle
- Gentle hair care; avoid tight hairstyles/traction; treat seborrheic dermatitis if present.
- Nutritional optimization if deficient (iron, vitamin D); supplements only if deficiency documented.
- Special considerations
- Pregnancy: avoid 5α-RIs, spironolactone, oral minoxidil; topical minoxidil typically avoided—discuss risk/benefit.
- Monitoring: photos, hair counts/part width, trichoscopy every 6–12 months.
References (recent guidelines and key reviews)
- International and AAD consensus on AGA diagnosis and treatment, 2022–2024.
- RCTs and meta-analyses of minoxidil (topical/oral), finasteride/dutasteride, PRP, and LLLT, 2021–2024.
- Women’s AGA and antiandrogen therapy reviews, 2022–2024.