Every hair on your scalp is independently cycling through four phases: anagen (growth), catagen (regression), telogen (rest), and exogen (shedding). Anagen lasts 2 to 7 years, catagen takes 2 to 3 weeks, and telogen persists for 3 to 6 months. Understanding these phases is the key to interpreting density tracking data accurately and avoiding false alarms about treatment failure.
Why Hair Cycling Matters for Tracking
When you take density readings with myhairline.ai over several months, you will see small fluctuations. These are not random noise. They reflect the natural turnover of follicles moving between growth and rest. At any moment, roughly 85 to 90% of your scalp follicles are in anagen, 1 to 2% are in catagen, and 10 to 15% are in telogen.
This means your density readings are always a snapshot of a moving system. A single low reading does not mean you are losing hair. A single high reading does not mean your treatment is working perfectly. Only the trend across multiple readings, spanning at least 6 to 12 months, reveals your true trajectory.
The Four Phases Explained
Anagen: The Growth Phase
Anagen is the active growth period when the hair follicle produces a visible shaft. This phase determines your maximum possible hair length.
| Anagen Detail | Value |
|---|---|
| Duration | 2 to 7 years |
| Percentage of follicles | 85-90% at any time |
| Growth rate | ~1 cm per month (0.35 mm/day) |
| Density contribution | Maximum, shaft fully present |
During anagen, the follicle is anchored deep in the dermis and actively producing keratin. Hairs in anagen are firmly rooted and resistant to shedding from normal brushing or washing. This is the phase you want to maximize with treatment.
Finasteride works primarily by extending the anagen phase. By reducing DHT levels, it allows follicles to remain in active growth longer. This is why finasteride halts further loss in 80 to 90% of users and produces visible regrowth in 65% of them. The regrowth occurs because miniaturized follicles re-enter a full anagen cycle.
Catagen: The Regression Phase
Catagen is a brief transitional period when the follicle detaches from its blood supply and begins to shrink.
| Catagen Detail | Value |
|---|---|
| Duration | 2 to 3 weeks |
| Percentage of follicles | 1-2% at any time |
| Growth rate | None (shaft production stops) |
| Density contribution | Shaft still visible but no longer growing |
This phase is short and affects very few follicles simultaneously. You are unlikely to detect catagen directly in density readings. However, a cluster of follicles entering catagen together (which can happen after seasonal triggers or stress) may produce a brief measurable dip.
Telogen: The Resting Phase
Telogen is the dormant phase when the old hair shaft sits loosely in the follicle while a new anagen hair begins forming beneath it.
| Telogen Detail | Value |
|---|---|
| Duration | 3 to 6 months |
| Percentage of follicles | 10-15% at any time |
| Shedding | 50 to 100 hairs per day is normal |
| Density contribution | Reduced, shaft loosely anchored |
Telogen is where most density fluctuations originate. A higher-than-normal percentage of follicles entering telogen simultaneously (telogen effluvium) produces noticeable thinning. Stress, illness, surgery, crash diets, and hormonal changes can all push follicles into telogen prematurely.
In tracking data, a telogen shift appears as a 5 to 15% density decline over 2 to 3 months, followed by recovery over the next 4 to 6 months as new anagen hairs replace them. This U-shaped pattern is the hallmark of a temporary telogen event, not progressive hair loss.
Exogen: The Shedding Phase
Exogen is the active release of the old telogen hair from the follicle. Some researchers consider it part of telogen, but it is functionally distinct because the new anagen hair is already growing beneath the shed hair.
| Exogen Detail | Value |
|---|---|
| Duration | Days to weeks |
| Daily shedding rate | 50 to 100 hairs |
| Density impact | Temporary, new shaft already in progress |
Exogen shedding is what you see in the shower drain or on your pillow. Counting shed hairs is unreliable for tracking because shedding varies dramatically by hair washing frequency, physical activity, and season. Density measurement is more reliable because it captures what remains on the scalp, not what falls off.
Seasonal Cycling Patterns in Tracking Data
Research shows that human hair has a seasonal shedding pattern. Telogen rates peak in late summer and early autumn (August to October in the Northern Hemisphere). This means your density readings may dip slightly during this period and recover in winter and spring.
| Season | Telogen Percentage | Expected Density Impact |
|---|---|---|
| Spring (Mar to May) | 10-12% | Stable to slightly increasing |
| Summer (Jun to Aug) | 12-15% | Gradual decline possible |
| Autumn (Sep to Nov) | 14-18% | Lowest readings of the year |
| Winter (Dec to Feb) | 10-12% | Recovery to baseline |
When reviewing your myhairline.ai tracking data, compare readings from the same season across different years. Comparing an October reading to a March reading will make treatment look ineffective when it may actually be working fine.
How Treatment Interacts with Hair Cycling
Finasteride and the Growth Cycle
Finasteride extends anagen and shortens telogen by reducing the DHT that miniaturizes follicles. In tracking data, this appears as:
- Months 1 to 3: Possible initial shedding as weak telogen hairs are pushed out by new anagen hairs
- Months 3 to 6: Density stabilization as new anagen hairs mature
- Months 6 to 12: Gradual density increase as previously miniaturized follicles produce thicker shafts
- Year 1 to 2: Peak improvement, then maintenance
The initial shedding phase is the most misinterpreted event in hair tracking. Users see a density dip in the first 1 to 3 months of finasteride and assume the drug is making things worse. In reality, this shedding indicates the drug is working. New anagen hairs are displacing the old, miniaturized telogen hairs.
Minoxidil and the Growth Cycle
Minoxidil stimulates anagen entry and prolongs anagen duration through vasodilation and potassium channel opening. In tracking data:
- Weeks 2 to 8: Significant shedding (more dramatic than finasteride) as telogen hairs are forced out
- Months 2 to 4: Density may appear worse than baseline
- Months 4 to 6: New, thicker anagen hairs become visible. Density begins recovering.
- Months 6 to 12: 40 to 60% of users see moderate improvement
Minoxidil shedding is typically more noticeable than finasteride shedding. The tracking data will show a deeper initial dip before recovery. This is normal and expected.
PRP and the Growth Cycle
Platelet-Rich Plasma therapy stimulates follicle stem cells and can push resting follicles back into anagen. At $500 to $2,000 per session, tracking density response to PRP is essential for determining whether to continue treatment. Studies show a 30 to 40% density increase in responders, but results vary significantly between individuals.
Reading Your Tracking Data: Phase-Aware Interpretation
Pattern 1: Small Fluctuation (Normal Cycling)
A density variation of 3 to 5% between consecutive monthly readings, with no sustained direction. This is normal telogen turnover.
Action: Continue current treatment. No changes needed.
Pattern 2: Seasonal Dip and Recovery
A 5 to 10% density decline over 2 to 3 months in late summer to autumn, followed by full recovery by winter.
Action: Note the seasonal pattern. Compare year-over-year, not month-over-month.
Pattern 3: Treatment-Induced Shedding
A 10 to 20% density drop in the first 1 to 3 months after starting finasteride or minoxidil, followed by recovery and improvement by month 6.
Action: Do not stop treatment. This shedding indicates response. Continue tracking.
Pattern 4: Sustained Decline (True Progression)
A downward trend across three or more consecutive readings spanning 6 to 12 months, with no recovery.
Action: Consult a dermatologist. Current treatment may need adjustment. Consider adding a second treatment or increasing dose.
Pattern 5: Telogen Effluvium Event
A sudden, diffuse density drop of 15 to 30% following a stressor (illness, surgery, crash diet), followed by gradual recovery over 6 to 9 months.
Action: Identify the trigger. Telogen effluvium is self-resolving once the trigger is removed.
Setting Up Phase-Aware Tracking
To get the most from your density tracking data, follow this protocol:
- Monthly readings: Take density photos at the same time of day, same lighting, same angle. Consistency removes variables.
- Log treatments: Record start dates, dose changes, and missed days for all medications and supplements. myhairline.ai timestamps correlate density changes with treatment events.
- Note stressors: Mark major life events, illnesses, surgeries, and diet changes. These help explain telogen shifts months later.
- 12-month minimum: Do not draw conclusions from fewer than 12 months of data. Hair cycling operates on multi-month timescales.
- Season-adjusted comparison: Always compare same-season readings across years for the most accurate trend assessment.
What Your Cycle Data Means Long Term
After 12 to 18 months of tracking, your data reveals your personal cycling pattern. You will know your seasonal baseline, your response to treatment, and whether your density is stable, improving, or declining. This information is more valuable than any single clinic visit because it captures the dynamic, cyclical nature of hair biology over time.
A dermatologist sees a snapshot. Your tracking data is the full movie. Bring your density tracking history and anagen to telogen ratio tracking data to consultations so your doctor can make informed decisions based on objective measurements, not a single examination.
Start Tracking Your Hair Cycle Today
Get your baseline density reading at myhairline.ai/analyze and begin building the dataset that separates normal cycling from real progression.
This content is for informational purposes only and does not constitute medical advice. Consult a board-certified dermatologist for diagnosis and treatment of hair loss conditions.