What is DHT?

DHT is a more potent androgen that binds to androgen receptors in target tissues, including the hair follicle.

In individuals with a genetic predisposition, DHT binds to receptors in the hair follicle, triggering a process called follicular miniaturization. This shortens the anagen (growth) phase and prolongs the telogen (resting) phase, resulting in progressively finer, shorter hairs until the follicle stops producing hair entirely.

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.

What is 5-Alpha Reductase

5-Alpha Reductase is an intracellular enzyme that catalyzes the conversion of testosterone to dihydrotestosterone (DHT).

There are 2 iso-forms of 5-Alpha Reductase: Type I & 2

Type I : 5-Alpha Reductase

Primary locations: Sebaceous glands, epidermis (skin), liver, brain, and adrenal glands.
Function: Involved in skin physiology, sebum production, and neurosteroid metabolism.
pH optimum: Functions optimally at pH 6.0–8.5 (neutral to alkaline).
Hair follicle role: Minor presence in the outer root sheath. Not the primary isoform in the dermal papilla.

Type II : 5-Alpha Reductase

Primary locations: Hair follicles (dermal papilla), prostate, seminal vesicles, epididymis, and liver (minor).
Function: Primary enzyme for DHT production in androgen-sensitive tissues including hair follicles and prostate.
pH optimum: Functions optimally at pH 5.0–6.0 (acidic).
Hair follicle role: Predominantly expressed in the dermal papilla and outer root sheath of scalp hair follicles.

Inheritance (Both Parents)

Maternal (X chromosome): Androgen receptor gene — explains correlation with maternal grandfather.
Paternal (autosomal): Other genes affecting follicle function, enzyme activity, inflammation.

Relevance to Pattern Hair Loss

Type II predominance: Research indicates that Type II 5-alpha-reductase is the primary isoform expressed in human scalp hair follicles, particularly in the dermal papilla cells.
Regional variation: Studies have shown that Type II enzyme activity may be higher in frontal and temporal scalp regions compared to occipital (donor) regions in individuals with pattern hair loss.
DHT production: Local DHT production within the hair follicle — via Type II enzymatic conversion — is considered more biologically relevant than circulating DHT levels.
Type I role: Type I may contribute to sebum production and skin health but is not considered the primary driver of hair follicle miniaturization.

Clinical observation: The differential distribution of Type II 5-alpha-reductase in susceptible scalp regions aligns with the patterned nature of androgenetic alopecia — affecting frontal, temporal, and crown areas while sparing the occipital donor zone.

5-Alpha Reductase Targeted Treatment

The question of which enzyme isoform to target in treating hair loss is informed by the tissue distribution and biological role of each type.

Type II Targeting

Rationale: Type II is the predominant isoform in hair follicles and the prostate.
Selectivity: Agents that selectively inhibit Type II reduce DHT production in hair follicles while potentially preserving Type I activity in skin and other tissues.
Clinical literature: Published studies have investigated Type II inhibition in the context of androgenetic alopecia and benign prostatic hyperplasia.

Type I Targeting

Rationale: Type I is present in skin, sebaceous glands, and brain. Its role in hair follicle miniaturization is less clearly established in current literature.
Considerations: Inhibition of Type I may affect sebum production and neurosteroid metabolism. The clinical significance of these effects continues to be studied.

Dual Targeting (Both Types)

Approach: Some research has examined agents that inhibit both Type I and Type II isoforms.
Trade-offs: Broader enzyme inhibition may result in more complete DHT reduction but also affects a wider range of tissues.
Current understanding: The relative importance of Type I versus Type II in hair loss continues to be investigated in clinical research.

Research Results: Medical literature indicates that Type II 5-alpha-reductase is the primary isoform in human scalp hair follicles. The clinical significance of Type I inhibition for hair loss treatment remains an area of ongoing investigation.

"Natural" 5-Alpha Reductase 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.

FAQ

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.

Q: Which enzyme type is more important for hair loss? Current research suggests Type II 5-alpha-reductase is the primary isoform in scalp hair follicles and plays a more direct role.

Q: Are there genetic differences in enzyme types? Yes. Genetic variations in the SRD5A2 gene (encoding Type II) have been studied in relation to pattern hair loss susceptibility.

Q: Does Type I affect hair at all? Type I is present in sebaceous glands and may influence scalp environment through sebum production, but its direct role in follicular miniaturization is less established.

Q: Why does donor hair resist DHT? Research indicates that occipital scalp follicles may have lower levels of Type II 5-alpha-reductase activity and androgen receptor expression compared to frontal follicles.

5 Alpha-Reductase & DHT