Terminal hair regrowth from Finasteride indicates true follicle reversal, while vellus regrowth alone does not guarantee long-term density improvement. Knowing which type you are growing changes how you interpret your tracking data and whether you need to add complementary treatments.
Terminal vs Vellus: What is the Difference?
Every hair on your scalp falls into one of three categories based on shaft diameter:
| Hair Type | Diameter | Appearance | Growth Length |
|---|---|---|---|
| Terminal | Over 60 micrometers | Thick, pigmented, visible | 30cm+ (2 to 6 year anagen) |
| Intermediate | 30 to 60 micrometers | Medium thickness, pigmented | Variable |
| Vellus | Under 30 micrometers | Fine, often colorless, barely visible | Under 2cm |
Androgenetic alopecia is the process of terminal hairs miniaturizing into vellus hairs through progressive DHT-driven follicle shrinkage. Finasteride reverses this process in some follicles by reducing DHT, allowing the follicle to produce thicker hair in the next growth cycle.
The critical question is: how far has this reversal gone? A follicle producing vellus hair that shifts to intermediate is improved but may not contribute meaningfully to visible density. A follicle producing terminal hair again represents a complete or near-complete reversal.
Step 1: Take a Baseline That Measures Diameter, Not Just Count
Before evaluating regrowth quality, you need a baseline that captures hair thickness. Standard density counts (follicular units per square centimeter) miss the quality dimension entirely.
When you scan with myhairline.ai, the AI analysis estimates shaft diameter categories across your scan area. Record:
- Total density count: Follicular units per cm2
- Thick hair percentage: Hairs estimated over 60 micrometers
- Thin hair percentage: Hairs estimated under 30 micrometers
- Average diameter estimate: Overall thickness indicator
This baseline tells you your starting ratio of terminal to miniaturized hairs. After 6 to 12 months on Finasteride, changes in this ratio reveal the quality of your regrowth.
Step 2: Understand the Regrowth Timeline
Finasteride regrowth does not appear as fully terminal hair overnight. The follicle recovers gradually over multiple growth cycles:
- Cycle 1 (months 3 to 6): Miniaturized follicle sheds its thin hair and enters a new anagen phase. The new hair may be only slightly thicker than the previous one.
- Cycle 2 (months 6 to 12): The follicle produces a thicker hair as the sustained low-DHT environment allows the dermal papilla to recover. Intermediate-thickness hairs appear.
- Cycle 3 (months 12 to 24): If the follicle is capable of full reversal, it now produces a hair close to or at terminal thickness.
Not all follicles complete all three cycles of recovery. Some stabilize at the intermediate stage. Your tracking data reveals where each zone stands in this progression.
Step 3: Scan Monthly and Track the Diameter Trend
Monthly scans from month 3 through month 24 capture the regrowth quality trajectory. Here is what to look for:
Positive trajectory (terminal regrowth):
- Density count increases AND average diameter increases
- Thin hair percentage decreases month over month
- Thick hair percentage increases month over month
- Regrowth is visible to the naked eye by month 9 to 12
Plateau trajectory (vellus or intermediate regrowth):
- Density count increases BUT average diameter stays flat or decreases
- New hairs are fine and barely visible
- Part-line coverage does not improve despite higher density numbers
- Thin hair percentage remains high or increases
Step 4: Compare Regrowth Quality by Zone
Different scalp zones may show different regrowth quality. Scan at least three areas:
| Zone | Typical Regrowth Quality on Finasteride |
|---|---|
| Frontal hairline | Often intermediate to terminal; responds well in early Norwood stages |
| Mid-scalp | Best regrowth zone; most likely to produce terminal hairs |
| Crown (vertex) | Variable; may produce more vellus than terminal initially |
| Temples | Slowest to respond; often produces intermediate hairs |
If your mid-scalp shows terminal regrowth but your hairline shows only vellus, your overall density number may look good while your visual appearance has not improved as much. Zone-specific tracking catches this discrepancy.
Step 5: Decide When to Add Minoxidil
If your month 12 data shows predominantly vellus or intermediate regrowth, adding Minoxidil can help push those follicles toward terminal hair production. Minoxidil works through a different mechanism (vasodilation and potassium channel opening) that complements Finasteride's DHT reduction.
The combination protocol:
- Continue Finasteride 1mg daily (maintains DHT suppression)
- Add Minoxidil 5% once or twice daily to the areas showing weak regrowth
- Continue tracking monthly for an additional 6 months
- Evaluate whether the combination produces thicker regrowth than Finasteride alone
Clinical data shows Minoxidil adds 40 to 60% moderate regrowth on its own. Combined with Finasteride, the complementary mechanisms can convert intermediate hairs to terminal that Finasteride alone could not.
Step 6: Set Realistic Expectations by Norwood Stage
Your Norwood stage at the time you started Finasteride predicts regrowth quality:
| Starting Norwood | Expected Regrowth Quality |
|---|---|
| Norwood 2 | Mostly terminal; high reversal potential |
| Norwood 3 | Mix of terminal and intermediate |
| Norwood 3V | Terminal at hairline, intermediate at vertex |
| Norwood 4 | Intermediate in most zones; some terminal at hairline |
| Norwood 5+ | Mostly vellus or intermediate; limited terminal regrowth |
Earlier intervention means more follicles are still in the early stages of miniaturization and have a higher chance of full terminal reversal. This is why tracking early, even at Norwood 2, provides the best long-term outcome data.
Interpreting Your 12-Month Regrowth Report
At the 12-month mark, export your complete tracking timeline from myhairline.ai. A positive regrowth quality report shows:
- Average diameter trend increasing across months 6 to 12
- At least 50% of new growth classified as intermediate or terminal
- Visual improvement visible in comparison photos
- Density count stable or increasing
If your 12-month data shows predominantly vellus regrowth with no upward diameter trend, your follicles may have miniaturized past the point of full reversal. This does not mean Finasteride is failing. It may still be preventing further loss. But it does mean additional treatments are needed for cosmetically meaningful regrowth.
Start Tracking Your Regrowth Quality
Take your first diameter-inclusive scan at myhairline.ai/analyze. Whether you are just starting Finasteride or are 6 months in, a scan today establishes the reference point for evaluating your regrowth quality over the next 12 months.
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Finasteride is a prescription medication with potential side effects in 2 to 4% of users. Consult your dermatologist for personalized treatment recommendations. myhairline.ai is a tracking tool, not a diagnostic or treatment platform.