Frontal and vertex follicles have up to 3x higher androgen receptor density than occipital follicles, and this single biological fact explains the entire pattern of male androgenetic alopecia. Understanding how androgen receptors distribute across your scalp, and tracking the density consequences zone by zone, gives you the data to target treatments where they matter most.
The Biology Behind Patterned Hair Loss
Androgenetic alopecia does not occur randomly. It follows a predictable pattern because androgen receptor (AR) density varies across distinct scalp zones. When dihydrotestosterone (DHT) circulates through the bloodstream, it binds to androgen receptors in hair follicles. The more receptors a follicle has, the more DHT it absorbs, and the faster it miniaturizes.
This is why the Norwood Scale exists. Hair loss progresses through numbered stages because follicles in different zones have different levels of androgen sensitivity.
Androgen Receptor Distribution by Zone
| Scalp Zone | Relative AR Density | Norwood Stage Affected | Typical Graft Need |
|---|---|---|---|
| Frontal hairline | Very high (2.5 to 3x baseline) | Norwood 2 to 3 | 800 to 2,200 grafts |
| Temporal points | High (2 to 2.5x baseline) | Norwood 2 to 3 | Included in hairline count |
| Vertex (crown) | High (2 to 3x baseline) | Norwood 3V to 5 | 2,000 to 4,500 grafts |
| Midscalp | Moderate (1.5 to 2x baseline) | Norwood 4 to 5 | Part of larger procedures |
| Parietal (sides) | Low (1x baseline) | Norwood 6 to 7 only | Rarely needed |
| Occipital (back) | Lowest (resistant) | Preserved in all stages | Donor zone, not recipient |
The occipital zone's low AR density is what makes hair transplants possible. Follicles extracted from the back of the head (FUE recovery: 7 to 10 days, graft survival: 90-95%) retain their DHT resistance when transplanted to the hairline or vertex.
How Androgen Receptors Drive Miniaturization
When DHT binds to an androgen receptor inside a hair follicle cell, it triggers a cascade that shortens the anagen (growth) phase and prolongs the telogen (resting) phase. Over multiple hair cycles, this produces:
- Thinner hair shafts: Terminal hairs (thick, pigmented) gradually become vellus hairs (thin, colorless)
- Shorter growth cycles: Each cycle produces a shorter hair before shedding
- Longer rest periods: Follicles spend more time dormant between growth cycles
- Eventual follicle death: After enough cycles of miniaturization, the follicle produces no visible hair
This process happens faster in zones with higher AR density because those follicles absorb more DHT per hair cycle. A frontal follicle with 3x the AR density of an occipital follicle will miniaturize approximately 3x faster under the same DHT exposure.
Mapping Your Personal AR Distribution Through Tracking
You cannot directly measure your androgen receptor density at home. But you can infer it from your zone-specific density data over time. The zones that lose density fastest are the zones with the highest functional AR density.
How to Build Your Personal AR Map
Month 1 to 3: Establish Zone Baselines
Use myhairline.ai to measure density in each of these zones:
- Left and right temples
- Central hairline
- Frontal midscalp
- Vertex (crown)
- Left and right parietal (sides)
- Occipital (back, for reference)
Record the density reading for each zone. Your occipital reading serves as your personal "100% baseline" since that zone is resistant to DHT.
Month 3 to 12: Track Zone-Specific Changes
Repeat the same measurements every 4 weeks. After 6 to 12 months, you will have enough data points to see which zones are declining and at what rate.
Calculate Zone Sensitivity Scores
For each zone, calculate:
- Percentage of density remaining compared to your occipital baseline
- Rate of density change per month
- Rank zones from most to least affected
This creates your personal androgen receptor distribution map.
Example Zone Sensitivity Data
| Zone | Month 0 Density | Month 6 Density | Monthly Rate | Sensitivity Rank |
|---|---|---|---|---|
| Left temple | 185 FU/cm2 | 168 FU/cm2 | -2.8/month | 1 (highest) |
| Right temple | 182 FU/cm2 | 170 FU/cm2 | -2.0/month | 2 |
| Vertex | 178 FU/cm2 | 169 FU/cm2 | -1.5/month | 3 |
| Frontal midscalp | 190 FU/cm2 | 185 FU/cm2 | -0.8/month | 4 |
| Left parietal | 195 FU/cm2 | 194 FU/cm2 | -0.2/month | 5 |
| Occipital | 200 FU/cm2 | 200 FU/cm2 | 0.0/month | 6 (lowest) |
This data tells you that your left temple has the highest functional AR density and is your most vulnerable zone. Treatment should prioritize this area.
Why Your Pattern Differs from Others
The Norwood Scale describes common patterns, but individual variation is significant. Some men progress through the classic hairline recession pattern (Norwood 2 to 3 to 4). Others start with vertex thinning (Norwood 3V) while their hairline remains intact. A smaller group experiences diffuse thinning across the top.
These variations map directly to individual differences in AR distribution:
| Pattern Type | AR Distribution | Norwood Progression |
|---|---|---|
| Hairline-first | Highest AR density at frontal hairline | N2, N3, N4 (front to back) |
| Vertex-first | Highest AR density at crown | N3V, N5 (crown expanding) |
| Simultaneous | Equal AR density front and top | N4, N5 (both zones at once) |
| Diffuse | Moderately elevated AR across entire top | Non-classic thinning pattern |
Your tracking data reveals which pattern you follow. This information is valuable for treatment planning and for hair transplant design if you eventually pursue surgical restoration.
Targeting Treatment to High-AR Zones
Once your tracking data identifies your most sensitive zones, you can focus treatment resources accordingly.
Topical DHT Suppression
Topical finasteride and dutasteride solutions can be applied directly to the zones with the highest density decline. This delivers the active ingredient where AR density is highest. Studies suggest topical finasteride reduces scalp DHT by up to 70% with lower systemic absorption than the oral 1mg dose.
Oral Finasteride Coverage
Oral finasteride (1mg daily) provides systemic DHT reduction of approximately 70%. It is effective across all zones simultaneously: 80-90% of users halt further loss, and 65% experience regrowth. Side effects occur in 2-4% of users and are reversible on discontinuation.
Minoxidil as Zone-Specific Booster
Apply minoxidil (40-60% regrowth efficacy) preferentially to your highest-sensitivity zones. While minoxidil works through a different mechanism (vasodilation and growth factor stimulation rather than DHT suppression), concentrating it on your most affected zones maximizes its impact where you need it most.
PRP for Targeted Density Recovery
Platelet-Rich Plasma therapy ($500 to $2,000 per session, 30-40% density increase) can be directed to specific zones. Your tracking data showing which zones have lost the most density helps your provider focus injections where the follicles need the most support.
The Donor Zone Advantage
The occipital zone's low AR density is permanent and genetically encoded. This is the principle of donor dominance: follicles transplanted from the back of the head retain their DHT resistance in their new location.
For patients tracking toward Norwood 4 (2,500 to 3,500 grafts needed) or Norwood 5 (3,000 to 4,500 grafts), understanding donor zone stability through tracking data helps plan the timing and scope of a transplant procedure. FUE extraction from the occipital zone (recovery: 7 to 10 days) harvests follicles that will resist DHT for a lifetime.
Average follicular unit density varies by ethnicity: Caucasian hair averages 200 FU/cm2, Asian hair averages 170 FU/cm2, and African hair averages 150 FU/cm2. These baseline differences affect how many grafts can be safely extracted while maintaining donor zone density (safe extraction limit: 45% of available grafts).
Connecting Your Data to Long-Term Planning
Your zone-specific density tracking data serves multiple purposes:
- Identifies your personal vulnerability pattern for targeted treatment
- Measures treatment effectiveness zone by zone
- Predicts future progression based on current decline rates
- Informs transplant planning by showing which zones will need grafts and when
- Documents response to treatment changes when you add or modify your regimen
The men who manage androgenetic alopecia most effectively are those who understand their personal AR distribution pattern and track their response to treatment with data, not guesswork.
Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. Androgenetic alopecia treatment should be discussed with a board-certified dermatologist. Finasteride and dutasteride require prescriptions. Side effects, while uncommon, should be discussed with your doctor before starting treatment.
Map Your Scalp Zones Today
Upload your scalp photos to myhairline.ai/analyze to get zone-by-zone density measurements. Your first scan establishes the baseline that reveals which zones are most sensitive to DHT and where to focus your treatment efforts.