Scalp hair shedding increases by up to 60% in autumn, creating a temporary density dip that can look alarming on a tracking chart if you do not know to expect it. This guide explains the science behind seasonal shedding, shows you how to identify the pattern in your myhairline.ai data, and helps you avoid making treatment changes based on a normal biological cycle.
This content is for informational purposes only and does not constitute medical advice.
The Science of Seasonal Hair Shedding
Human hair follows a growth cycle with three phases: anagen (growth, lasting 2 to 7 years), catagen (transition, lasting 2 to 3 weeks), and telogen (rest, lasting 2 to 4 months). At any given time, approximately 85 to 90% of your scalp hair is in anagen and 10 to 15% is in telogen.
Research published in the British Journal of Dermatology found that the proportion of hairs entering telogen peaks in July, with the resulting shedding peaking in September through November. This is why many people notice increased hair fall on their pillow, in the shower, and on their brush during autumn months.
| Month | Telogen Entry Rate | Shedding Level | Density Impact |
|---|---|---|---|
| January to March | Low | Minimal shedding | Stable/recovering |
| April to June | Moderate | Normal shedding | Stable |
| July to August | Peak telogen entry | Shedding starting to increase | Beginning of dip |
| September to November | Declining entry, peak shed | Maximum shedding | Lowest density point |
| December | Low | Shedding normalizing | Recovery beginning |
The evolutionary explanation is that thicker hair growth in winter protects the scalp from cold, while summer sun triggers a partial telogen release. The practical impact is a temporary density dip of 5 to 15% that recovers naturally over the following 3 to 4 months.
Why Seasonal Shedding Confuses Treatment Tracking
If you start finasteride in April and take your monthly density readings through September, your data may show 3 months of stable or improving density followed by a density dip in September or October. Without understanding seasonal shedding, this dip looks like treatment failure.
The misinterpretation leads to one of two costly mistakes:
- Abandoning a working treatment: You stop finasteride because you think it stopped working, when the density dip was seasonal and would have recovered on its own.
- Adding unnecessary treatments: You add minoxidil or schedule PRP sessions ($500 to $2,000 each) to address a temporary seasonal dip that would have resolved without intervention.
Both mistakes waste time and money. Both are preventable with seasonal awareness in your tracking data.
How to Build a Seasonal Baseline
The first year of tracking establishes your personal seasonal pattern. Take monthly readings with myhairline.ai for 12 consecutive months. Your data will show:
- Which months have your highest density (typically late winter/spring)
- Which months have your lowest density (typically autumn)
- The magnitude of your personal seasonal variation
Once you have this baseline, you compare subsequent readings to the same month in the previous year rather than to the previous month. Year-over-year comparison at the same calendar point eliminates seasonal noise from your trend analysis.
Year 1 October reading: Norwood 3 (your first autumn dip on record)
Year 2 October reading: Norwood 3 (same as year 1, meaning no progression)
Year 2 October reading: Norwood 3.5 (worse than year 1, suggesting genuine progression beyond seasonal variation)
This year-over-year comparison is the most reliable method for distinguishing seasonal shedding from treatment failure or progressive androgenetic alopecia.
Seasonal Tracking Calendar
Use this framework for your monthly readings:
| Quarter | Expected Pattern | Tracking Focus |
|---|---|---|
| Q1 (Jan to Mar) | Recovery and peak density | Best time to assess true baseline density |
| Q2 (Apr to Jun) | Stable density, pre-shed | Good window for treatment start dates |
| Q3 (Jul to Sep) | Telogen entry increasing, early shedding | Expect density dip, do not change treatments |
| Q4 (Oct to Dec) | Peak shedding, then recovery begins | Compare to prior year Q4, not to Q2 |
If you are currently on finasteride (80 to 90% halt further loss) or minoxidil (40 to 60% regrowth), maintain your treatment protocol through seasonal dips. These medications work on the follicular cycle, not on seasonal shedding patterns. Stopping treatment during a seasonal dip does not address the shedding and may restart androgenetic alopecia progression.
For a broader understanding of telogen-phase shedding and recovery, see our telogen effluvium recovery guide.
When a Seasonal Dip Is Not Seasonal
Your tracking data should raise concern if any of the following occur:
- The density dip is significantly larger than the same period in the previous year
- Density does not recover to near-baseline levels within 3 to 4 months after the dip
- The dip follows the Norwood pattern (temples and vertex) rather than a diffuse pattern
- The shedding started outside the typical July to November window
Any of these patterns suggests that something beyond seasonal variation is driving the loss. Consult a dermatologist and bring your myhairline.ai tracking data showing the year-over-year comparison. For step-by-step guidance on tracking progression patterns, see how to track hair loss progression.
The Bottom Line
Seasonal shedding is normal, temporary, and recoverable. It happens to everyone, regardless of treatment status. The only way to prevent it from triggering unnecessary panic or treatment changes is to track density over a full annual cycle and compare year-over-year rather than month-to-month.
Start building your seasonal baseline with a free reading at myhairline.ai/analyze.