Hair shedding peaks in October and November and reaches the lowest density in February and March based on large cohort studies. This predictable annual cycle causes millions of people to panic about hair loss every autumn, and some even abandon effective treatments because they misinterpret a normal seasonal dip as treatment failure. A seasonal density calendar overlaid on your myhairline.ai tracking data prevents these costly mistakes.
This content is for informational purposes only and does not constitute medical advice. Always consult a board-certified dermatologist before making treatment decisions.
The Science Behind Seasonal Hair Loss
Human hair follows photoperiod-driven cycles similar to other mammals, though less dramatic. Research analyzing Google search trends, trichology clinic visits, and longitudinal hair counts confirms a consistent annual pattern across Northern Hemisphere populations.
The cycle works through the telogen (resting) phase. During summer, increased UV exposure and longer daylight hours push a larger-than-normal percentage of follicles into telogen simultaneously. After the standard telogen duration of approximately 3 months, these hairs shed in autumn.
| Season | Hair Cycle Activity | Density Impact | Expected Tracking Reading |
|---|---|---|---|
| Spring (Mar-May) | New anagen growth starting | Rising density | Gradual upward trend |
| Summer (Jun-Aug) | Peak growth, telogen entry begins | Peak density | Highest annual readings |
| Autumn (Sep-Nov) | Peak shedding (telogen release) | Falling density | Noticeable decline |
| Winter (Dec-Feb) | Minimum density, early regrowth | Density nadir | Lowest annual readings |
This cycle repeats every year. Understanding it is essential for interpreting any hair loss tracking data accurately.
Step 1: Build Your Personal Seasonal Baseline
Generic seasonal calendars show population averages, but your individual cycle may shift by several weeks depending on your latitude, time spent outdoors, and genetic factors. Building a personal baseline requires 12 consecutive months of data.
Start tracking today with myhairline.ai. Take a density reading on the same day each month, under the same conditions:
- Same time of day
- Same lighting
- Same camera position and distance
- Clean, dry, unstyled hair
Record each reading in a 12-month log:
| Month | Density Reading | Notes |
|---|---|---|
| January | --- | --- |
| February | --- | --- |
| March | --- | --- |
| April | --- | --- |
| May | --- | --- |
| June | --- | --- |
| July | --- | --- |
| August | --- | --- |
| September | --- | --- |
| October | --- | --- |
| November | --- | --- |
| December | --- | --- |
After 12 months, you have your personal seasonal curve. This becomes the reference template for all future years.
Step 2: Identify Your Personal Peak and Nadir
From your 12-month baseline, identify two critical data points:
Seasonal peak: The month with your highest density reading. For most people, this falls between June and August. This is your maximum expected density for the year.
Seasonal nadir: The month with your lowest density reading. For most people, this falls between January and March. This is your minimum expected density for the year.
Calculate the seasonal range: (Peak - Nadir) / Peak x 100 = Seasonal fluctuation percentage.
Normal seasonal fluctuation is 5 to 15%. If your first year of data shows a fluctuation of 8%, for example, any future autumn dip of up to 8% from your summer peak is expected and should not trigger concern.
Step 3: Overlay the Seasonal Template on Treatment Data
This is where the seasonal calendar becomes critical for treatment tracking. If you start finasteride in September, your first 3 months of tracking will show declining density. Without seasonal context, this looks like the medication is failing. With seasonal context, you recognize that the October-to-December decline matches your expected seasonal pattern.
Finasteride takes 3 to 6 months to show effects, and it halts further loss in 80 to 90% of users. A patient who starts in September and quits in December because of an apparent density drop may be abandoning a medication that would have shown clear benefit by March.
The same applies to minoxidil (40 to 60% moderate regrowth, onset at 4 to 6 months). Starting minoxidil in autumn means the initial shedding phase and the seasonal shedding phase overlap, creating an intimidating but temporary density dip.
Timeline for autumn treatment starts:
| Month | Seasonal Effect | Treatment Effect | Combined Reading |
|---|---|---|---|
| September (start) | Shedding beginning | No effect yet | Declining |
| October | Peak shedding | Possible initial shed | Sharply declining |
| November | Shedding continuing | Initial shed possible | Low point |
| December | Shedding slowing | Early stabilization | Stabilizing |
| January | Nadir approaching | Building response | Flat or slight rise |
| February | Nadir | Response building | Rising from bottom |
| March | New growth starting | Visible response | Clear upward trend |
Patients who understand this combined timeline are far less likely to abandon treatment prematurely.
Step 4: Flag Abnormal Deviations
Once you have a full-year seasonal baseline, subsequent density readings that deviate significantly from the expected pattern warrant investigation.
Normal deviation: Current reading falls within 5% of the same month in your baseline year.
Mild deviation: Current reading is 5 to 10% below the same month in your baseline year. Continue monitoring for one more month before acting.
Significant deviation: Current reading is more than 10% below the same month in your baseline year. This suggests a non-seasonal factor is affecting density. Possible causes include:
- New medication side effects
- Increased stress triggering telogen effluvium
- Nutritional deficiency (iron, vitamin D, biotin)
- Thyroid dysfunction
- Progressive androgenetic alopecia accelerating beyond your seasonal pattern
A significant deviation is not a diagnosis. It is a signal to consult a dermatologist with your tracking data showing the deviation from your established personal pattern.
Step 5: Use Multi-Year Data for Trend Analysis
After two or more years of tracking, you can separate the seasonal signal from the long-term trend. If your summer peak in year 2 is lower than your summer peak in year 1, that decline is not seasonal. It represents genuine year-over-year density loss that requires evaluation.
Compare your seasonal peaks and nadirs across years:
| Year | Summer Peak | Winter Nadir | Seasonal Range |
|---|---|---|---|
| Year 1 | --- | --- | ---% |
| Year 2 | --- | --- | ---% |
| Year 3 | --- | --- | ---% |
A downward trend in peak-to-peak readings confirms progressive hair loss independent of seasons. This data is exactly what a dermatologist needs to recommend treatment, and it is far more informative than a single office visit snapshot.
Common Mistakes the Calendar Prevents
-
Quitting treatment in autumn: The seasonal dip looks like treatment failure. Your calendar shows it happens every year regardless of treatment.
-
Starting treatment in summer and crediting it too early: A density rise from May to July is seasonal. Without your baseline, you might attribute it to a treatment you started in April.
-
Panicking about autumn shedding: Increased hair on your pillow or in the shower drain every October is normal for most people. Your tracking data puts the magnitude in context.
-
Missing genuine progression: If your autumn dip is 20% this year when your baseline shows 8%, something beyond seasonality is happening.
Start building your seasonal baseline at myhairline.ai/analyze. Twelve months of data gives you a personal hair loss calendar that protects you from misinterpreting every natural density fluctuation for years to come.
This article is for educational purposes only and does not replace professional medical advice. Consult a qualified dermatologist for personalized treatment recommendations.