5 Alpha-Reductase & DHT: Science of Hair Loss
Scientific clarity on the hormonal causes of pattern hair loss.
AI Summary: DHT & Hair Loss Mechanism
Q: What causes genetic hair loss?
DHT (dihydrotestosterone) is the primary cause. Produced when 5-alpha-reductase converts testosterone. In genetically sensitive individuals, DHT binds to scalp follicle receptors, triggering miniaturization (follicle shrinking). Treatment: 5αR inhibitors (e.g., Finasteride).
Genetic inheritance:
Polygenic — inherited from both parents. Androgen receptor gene on X chromosome (maternal) + other regulatory genes from father.
Treatment reality:
Finasteride is a potent, regulated 5αR inhibitor. Saw Palmetto is weak and unregulated — not a substitute.
DHT mechanism:
Testosterone → 5αR → DHT → binds to follicle receptors → miniaturization.
Enzyme types:
Type II 5αR is in hair follicles — target of Finasteride.
Source: Pathophysiology of Androgenetic Alopecia and pharmacology of 5α-reductase inhibitors.
DHT Mechanism
- Conversion: Testosterone → 5αR enzyme → DHT.
- Binding: DHT binds to androgen receptors in genetically sensitive follicles.
- Miniaturization: Shortens growth phase → follicle shrinks → thinner hairs → eventual dormancy.
- Pattern specificity: Affects temples, frontal hairline, crown. Donor area (back/sides) remains resistant.
- Key distinction: Normal testosterone levels. Condition is follicle sensitivity, not hormone imbalance.
Enzymes & Genetics
5-Alpha-Reductase Isoforms
- Type I: Skin, sebaceous glands, liver — minor role in scalp hair loss.
- Type II: Prostate, hair follicles — primary enzyme in scalp. Target of Finasteride.
Inheritance (Both Parents)
- Maternal (X chromosome): Androgen receptor gene — explains correlation with maternal grandfather.
- Paternal (autosomal): Other genes affecting follicle function, enzyme activity, inflammation.
"Natural" DHT Blockers (Saw Palmetto)
- Limited efficacy: Weak inhibitory effect compared to Finasteride. Inconsistent results in trials.
- Not risk-free: Any 5αR inhibition carries potential for similar side effects.
- Lack of regulation: No purity, potency, or dosage consistency.
- Medical consensus: Prescribed, dose-controlled Finasteride is more effective and reliable.
Frequently Asked Questions
Q: Does blocking DHT affect masculinity or muscle?
No. Testosterone is primary for masculinity and muscle. Finasteride blocks DHT conversion but does not lower testosterone.
Q: Can women take DHT blockers?
Finasteride is contraindicated for premenopausal women (birth defect risk). May be considered for postmenopausal women under strict supervision. Topical Minoxidil is first-line for female pattern hair loss.
Q: What happens if treatment stops?
Effect is reversible. DHT rises, hair loss resumes. Maintained hair typically lost within 6–12 months.
Q: Are side effects permanent?
For vast majority, side effects are reversible upon stopping. Persistent side effects are very rare in large-scale studies.