What is the role of Dihydrotestosterone (DHT) in hair loss and how can it be treated?

Role of DHT in Hair Loss and Treatment Options

Dihydrotestosterone (DHT) is the primary driver of androgenetic alopecia (male pattern hair loss) by causing miniaturization of hair follicles, and can be effectively treated with 5α-reductase inhibitors like finasteride which block the conversion of testosterone to DHT.

Mechanism of DHT in Hair Loss

• DHT is formed when the enzyme 5α-reductase converts testosterone to DHT in the scalp, liver, and skin 1
• DHT is a potent androgen that binds to androgen receptors in hair follicle cells, causing:
  • Miniaturization of hair follicles 2
  • Shortening of the anagen (growth) phase of the hair cycle 2
  • Prolongation of the telogen (resting) phase 2
• DHT remains bound to receptors for approximately 53 minutes compared to 35 minutes for testosterone, making it more potent 3
• This process leads to progressively thinner, shorter, and less pigmented hairs over time 2

Treatment Options

5α-Reductase Inhibitors

• Finasteride is a specific inhibitor of Type II 5α-reductase that blocks conversion of testosterone to DHT 1
  • Forms a stable enzyme complex with 5α-reductase with slow turnover (half-life ~30 days) 1
  • Oral finasteride 1mg daily reduces scalp DHT levels by approximately 64% 4
  • Clinical studies show that finasteride 1mg/day:
    • Increases hair count (107 and 138 hairs vs placebo at 1 and 2 years) 5
    • Slows progression of hair loss in 83% of men after 2 years 6
    • Improves hair growth in 48% of men at 1 year and 66% at 2 years 6
  • Side effects include sexual function disorders (decreased libido, ejaculation disorder, erectile dysfunction) in 3.8% of patients 6

Topical Treatments

• Minoxidil is an FDA-approved topical treatment that:
  • Works through a different mechanism than finasteride
  • Promotes hair growth but does not directly affect DHT levels 2
  • Often used in combination with finasteride for enhanced results

Herbal Alternatives

• Several herbal treatments have shown potential to inhibit 5α-reductase activity:
  • Saw palmetto (Serenoa repens)
  • Green tea (Camellia sinensis)
  • Pumpkin seed (Curcurbita pepo)
  • Rosemary (Rosmarinus officinalis) 3
  • However, these have less robust clinical evidence compared to pharmaceutical options

Treatment Selection Considerations

• Efficacy: Finasteride has the strongest evidence for reducing DHT and improving hair growth 6, 5
• Side effects: Sexual side effects occur in a small percentage of finasteride users but typically resolve with discontinuation 6
• Treatment duration: Continuous treatment is necessary as hair loss will resume when treatment is stopped 5
• Patient factors: Age, extent of hair loss, and medical history should guide treatment selection 2

Common Pitfalls and Caveats

• DHT reduction requires ongoing treatment; discontinuation leads to resumption of hair loss within months 1
• Maximum DHT reduction occurs at finasteride doses as low as 0.2mg daily, though 1mg is the standard dose 4
• Finasteride is contraindicated in pregnant women due to risk of hypospadias in male fetuses 6
• Results from treatment typically take 3-6 months to become visible, and maximum benefit may not be seen until 1-2 years of continuous treatment 5
• Early intervention produces better results, as treatment is more effective at preventing further loss than regrowing already lost hair 2