Dihydrotestosterone (DHT) is the primary hormone responsible for male pattern baldness, driving the miniaturization process that turns thick terminal hair into thin vellus hair over months and years. Understanding exactly how DHT works on your follicles is the first step toward choosing the right treatment.
This guide covers the biology of DHT, the hormonal cascade that causes hair loss, and the proven methods for interrupting it.
How DHT Is Produced
Testosterone, the primary male sex hormone, is converted into DHT by an enzyme called 5-alpha reductase. This conversion happens in several tissues throughout the body, including the scalp, prostate, and skin.
There are two types of 5-alpha reductase:
- Type I: Found primarily in the skin and sebaceous glands
- Type II: Found primarily in the hair follicles and prostate
Type II is the main driver of scalp hair loss. Men with androgenetic alopecia have higher levels of 5-alpha reductase activity in their scalp tissue and higher concentrations of DHT in their follicles compared to men without hair loss.
The Conversion Process
| Step | What Happens | Location |
|---|---|---|
| 1 | Testes produce testosterone | Bloodstream |
| 2 | Testosterone reaches scalp tissue | Hair follicle |
| 3 | 5-alpha reductase converts testosterone to DHT | Dermal papilla |
| 4 | DHT binds to androgen receptors | Hair follicle bulge |
| 5 | Binding triggers miniaturization signals | Follicle shrinks |
Why Only Some Follicles Are Affected
DHT circulates throughout the entire scalp, yet hair on the back and sides remains unaffected. The difference is genetic. Follicles on the top and front of the scalp carry androgen receptors that are programmed to respond to DHT. Follicles on the occipital and temporal regions (back and sides) lack these receptors.
This genetic programming explains several important facts:
- Hair transplants work because relocated follicles keep their original DHT resistance
- Two brothers can have very different hair loss patterns despite similar DHT levels
- Some men have high testosterone and no hair loss, while others with lower testosterone lose hair rapidly
The key factor is not how much DHT you produce, but how your follicles respond to it. For a full breakdown of androgenetic alopecia causes, including the genetic inheritance patterns involved, see our detailed guide.
The Miniaturization Timeline
When DHT binds to a susceptible follicle's androgen receptor, it does not kill the follicle immediately. Instead, it triggers a gradual process:
- Anagen phase shortens: The active growth phase drops from 2 to 6 years to progressively shorter periods
- Telogen phase lengthens: The resting phase between growth cycles increases
- Hair caliber decreases: Each cycle produces thinner, shorter, less pigmented hair
- Follicle shrinks: The dermal papilla and follicle bulge physically reduce in size
- Vellus conversion: Terminal hair becomes fine, colorless vellus hair
This entire process can take 5 to 15 years per follicle. Because different follicles are at different stages, the overall effect is gradual thinning rather than sudden baldness. The Norwood scale maps how this pattern typically progresses across the scalp.
Hormonal Factors Beyond DHT
While DHT is the primary driver, several other hormonal factors influence androgenetic alopecia:
Cortisol and Stress Hormones
Chronic stress elevates cortisol, which can disrupt the hair growth cycle. High cortisol does not cause androgenetic alopecia, but it can accelerate loss in men who already have the genetic predisposition. It also triggers telogen effluvium, a temporary shedding condition that makes pattern baldness appear worse.
Thyroid Hormones
Both hypothyroidism and hyperthyroidism can cause diffuse hair thinning. If your hair loss does not follow the typical Norwood pattern (temples and crown), your dermatologist should check thyroid function before assuming androgenetic alopecia.
Insulin and IGF-1
Insulin resistance has been linked to higher 5-alpha reductase activity. Men with metabolic syndrome may experience faster hair loss progression. This is one reason why diet and exercise can play a supporting role in hair loss management.
How DHT-Blocking Treatments Work
Finasteride
Finasteride inhibits Type II 5-alpha reductase, reducing scalp DHT levels by approximately 60 to 70%. At 1mg daily:
- 80 to 90% of users halt further hair loss
- 65% experience measurable regrowth
- 2 to 4% experience sexual side effects, which are reversible on discontinuation
- Results typically appear at 3 to 6 months
Dutasteride
Dutasteride inhibits both Type I and Type II 5-alpha reductase, reducing DHT by approximately 90%. It is more effective than finasteride but carries a higher side effect profile. It is FDA approved for benign prostatic hyperplasia (BPH) and used off-label for hair loss.
Topical DHT Blockers
Topical finasteride and other formulations aim to reduce scalp DHT without significantly lowering systemic DHT levels. This approach may reduce the risk of systemic side effects while maintaining local efficacy, though long-term studies are still ongoing.
Why Transplanted Hair Resists DHT
Hair transplant surgery works because of a principle called donor dominance. Follicles from the back and sides of the scalp are genetically resistant to DHT. When these follicles are relocated to the hairline or crown, they retain that resistance permanently.
This is why:
- FUE grafts (up to 5,000 per session) achieve 90 to 95% survival rates
- Transplanted hair continues growing for life
- The safe extraction limit is 45% of donor follicles to preserve the donor area's appearance
To check your hair transplant candidacy, consider your current Norwood stage and donor area density.
Practical Takeaways
DHT is the primary cause of male pattern baldness, but it is also the most treatable aspect. Blocking DHT with finasteride or dutasteride is the single most effective non-surgical intervention. For men who want to restore density beyond what medication can achieve, hair transplantation offers a permanent solution because of the inherent DHT resistance in donor follicles.
The most important step is confirming your hair loss type before starting any treatment. Misdiagnosis leads to wrong treatment in roughly 28% of cases.
Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. Always consult a board-certified dermatologist or hair restoration specialist for diagnosis and treatment recommendations specific to your situation.
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