News & Insights

Understanding Hair Growth and Hair Loss: Evidence-Based Insights and FDA-Approved Treatments

November 24, 2025
Hair Growth and Hair Loss

Hair loss is one of the most common reasons patients seek dermatologic care, with significant psychosocial impact. Advances in molecular biology and immunology have revealed that hair follicles are dynamic mini organs with immune, hormonal, and regenerative functions.¹ Recent studies highlight the role of inflammation, hormonal signaling, and immune privilege disruption in the pathogenesis of alopecia. This article reviews the biology of hair growth, major causes of hair loss, and US Food and Drug Administration (FDA)-approved treatments. 

The Biology of Hair Growth 

Hair follicles cycle through anagen (growth), catagen (regression), and telogen (rest) phases. Wnt/β-catenin signaling and androgen receptor activity maintain anagen, while immune privilege shields follicles from autoimmune attack.² Disruption of these pathways—by genetic, hormonal, or immune mechanisms—leads to asynchronous cycling and visible thinning or shedding. These insights have paved the way for targeted molecular therapies such as Janus kinase (JAK) inhibitors. 

Major Causes of Hair Loss 

Androgenetic Alopecia (AGA) 

AGA, or pattern hair loss, results from progressive follicular miniaturization driven by dihydrotestosterone (DHT) in genetically predisposed follicles.³ It affects up to 80% of men and 40% of women. 

Alopecia Areata (AA) 

AA is an autoimmune condition in which autoreactive CD8⁺ T cells attack anagen follicles, breaching immune privilege.⁴ 

Telogen Effluvium (TE) 

TE is caused by premature follicular transition into the telogen phase, often triggered by systemic stressors such as illness, surgery, or hormonal shifts. The COVID-19 pandemic increased awareness of post-infectious TE, typically presenting 2 to 3 months after infection with spontaneous regrowth.5 

Scarring Alopecias 

Cicatricial (scarring) alopecias, including lichen planopilaris, frontal fibrosing alopecia, and central centrifugal cicatricial alopecia (CCCA), cause irreversible follicular destruction and fibrosis.⁶ 

FDA-Approved Therapies for Hair Loss 

AGA 

  • Topical minoxidil (2% and 5%): FDA approved for men and women, topical minoxidil enhances follicular blood flow and prolongs anagen.⁷ 
  • Finasteride 1 mg: FDA approved for male AGA, finasteride inhibits type II 5-α-reductase, lowering DHT. The European Medicines Agency (EMA) updated labeling in 2025 regarding suicidal ideation risk.⁸ 
  • Low-level laser therapy (LLLT): FDA-cleared devices show modest improvements in hair density when used adjunctively.⁹ 

AA 

The JAK inhibitor era has transformed severe AA management: 

  • Baricitinib (JAK 1/2 inhibitor) was approved in 2022 for adults with severe AA.10 
  • Ritlecitinib (JAK 3/TEC inhibitor) received approval in 2023 for patients ≥ age 12 years. 
  • Deuruxolitinib (JAK 1/2 inhibitor) was approved in 2024, providing an additional oral option for adults. 

TE and Scarring Alopecias 

No FDA-approved drugs exist for TE or cicatricial alopecias; management focuses on identifying triggers, reducing inflammation, and preventing permanent loss.⁶ Off-label modalities, such as low-dose oral minoxidil, microneedling, and platelet-rich plasma (PRP), are supported by emerging evidence.11,12 

Emerging Research and Clinical Insights (2023–2025) 

  • Oral vs topical minoxidil: A 2024 randomized controlled trial found 5 mg oral minoxidil comparable to topical 5% minoxidil for male AGA, with predictable hypertrichosis.13
  • Microneedling adjunct: Meta-analyses confirm microneedling enhances topical minoxidil efficacy.11
  • PRP optimization: Double-spin PRP methods yield more consistent platelet concentrations and clinical outcomes.12

 

Clinical Challenges 

Patient Misconceptions 

Patients often conflate FDA approval with FDA clearance; pharmacologic agents, such as minoxidil and finasteride, are approved, whereas LLLT devices are cleared for safety equivalence. 

Safety Monitoring 

The 2025 EMA finasteride update highlights psychiatric risk screening. For JAK inhibitors, baseline and periodic laboratory monitoring are mandatory. 

Adherence and Expectations 

Hair regrowth typically requires 3 to 6 months and can take 9 to 12 months or more for noticeable improvement; counseling should reinforce treatment adherence and realistic timelines. 

Health Equity 

Persistent disparities in diagnosing and managing CCCA among Black women necessitate early trichoscopic screening and culturally competent care.14 

Conclusion 

The management of hair loss has evolved into a mechanism-driven, evidence-based field. FDA-approved treatments now address both hormonal and autoimmune pathways. Ongoing research into follicular immunobiology and regenerative medicine will continue to expand therapeutic options and improve outcomes for diverse patient populations. 

References 

  1. Schneider MR, Schmidt-Ullrich R, Paus R. The hair follicle as a dynamic miniorgan. Curr Biol. 2009;19(3):R132-R142. doi:10.1016/j.cub.2008.12.005 
  2. Gilhar A. Collapse of immune privilege in alopecia areata: coincidental or substantial? J Invest Dermatol. 2010;130(11):2535-2537. doi:10.1038/jid.2010.260 
  3. Cortez GL, Hassun K, Linhares LRP, Florenço V, Pinheiro MVB, do Nascimento MM. Male androgenetic alopecia. An Bras Dermatol. 2025;100(2):308-321. doi:10.1016/j.abd.2024.08.004  
  4. Villasante Fricke AC, Miteva M. Epidemiology and burden of alopecia areata: a systematic review. Clin Cosmet Investig Dermatol. 2015;8:397-403. doi:10.2147/CCID.S53985 
  5. Mieczkowska K, Deutsch A, Borok J, et al. Telogen effluvium: a sequela of COVID-19. Int J Dermatol. 2021;60(1):122-124. doi:10.1111/ijd.15313  
  6. Alenezi S, Ezzat R, Miteva M. Frontal fibrosing alopecia (FFA) part I—diagnosis and clinical presentation. J Am Acad Dermatol. 2025;S0190-9622(25)00040-4. doi:10.1016/j.jaad.2024.10.126 
  7. Olsen EA, Dunlap FE, Funicella T, et al. A randomized clinical trial of 5% topical minoxidil versus 2% topical minoxidil and placebo in the treatment of androgenetic alopecia in men. J Am Acad Dermatol. 2002;47(3):377-385. doi:10.1067/mjd.2002.124088 
  8. Measures to minimise risk of suicidal thoughts with finasteride and dutasteride medicines. European Medicines Agency. May 8, 2025. Accessed November 18, 2025. https://www.ema.europa.eu/en/news/measures-minimise-risk-suicidal-thoughts-finasteride-dutasteride-medicines 
  9. Zarei M, Wikramanayake TC, Falto-Aizpurua L, Schachner LA, Jimenez JJ. Low level laser therapy and hair regrowth: an evidence-based review. Lasers Med Sci. 2016;31(2):363-371. doi:10.1007/s10103-015-1818-2 
  10. King B, Ohyama M, Kwon O, et al. Two phase 3 trials of baricitinib for alopecia areata. N Engl J Med. 2022;386(18):1687-1699. doi:10.1056/NEJMoa2110343 
  11. Pei D, Zeng L, Huang X, Wang B, Liu L, Zhang G. Efficacy and safety of combined microneedling therapy for androgenic alopecia: a systematic review and meta-analysis of randomized clinical trials. J Cosmet Dermatol. 2024;23(5):1560-1572. doi:10.1111/jocd.16186 
  12. Xiao C, Zhang GH, Li HQ, Yang PP, Zhang HB, Mu YX. Meta-analysis of efficacy of platelet-rich plasma combined with minoxidil for androgenetic alopecia. Aesthetic Plast Surg. 2024;48(21):4554-4566. doi:10.1007/s00266-024-04054-6 
  13. Penha MA, Miot HA, Kasprzak M, Müller Ramos P. Oral minoxidil vs topical minoxidil for male androgenetic alopecia: a randomized clinical trial. JAMA Dermatol. 2024;160(6):600-605. doi:10.1001/jamadermatol.2024.0284 
  14. Jackson T, Sow Y, Dinkins J, et al. Treatment for central centrifugal cicatricial alopecia—Delphi consensus recommendations. J Am Acad Dermatol. 2024;90(6):1182-1189. doi:10.1016/j.jaad.2023.12.073 
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