Late-Summer Hair Loss: Why It Peaks in September

Every September, the same thing happens in clinics across Europe. The phone starts ringing, and the sentence is almost always identical: “I came back from holiday and my hair is falling out.”

The shower drain looks worse. There is more hair on the pillow, more on the brush, more in your hand when you run your fingers through it. And because it happens right after the most relaxed weeks of the year, it feels completely unfair.

Here is the part almost nobody explains: the hair you are losing in September was not damaged in September. It stopped growing in June and July. What you are seeing now is a delayed release, on a biological schedule that is roughly a hundred days long.

That distinction matters, because it separates two very different situations. One resolves on its own by late autumn. The other is the early, visible edge of a permanent condition — and every month you spend calling it “just the season” is a month of density you do not get back.

This article explains the mechanism, gives you a way to measure what is actually happening on your own head, and sets out the five signs that mean this is no longer seasonal.

The 100-day rule: why September, not August

Your hair does not grow continuously. Each follicle runs an independent cycle with three phases:

• Anagen — the active growth phase, lasting 2 to 6 years. At any moment, roughly 85–90% of your hair is here.
• Catagen — a short transition phase of 2 to 3 weeks.
• Telogen — the resting phase, lasting around 3 months. The hair is finished, anchored but no longer growing. At the end of telogen, it is pushed out by the new hair forming beneath it.

The critical point is that shedding is not the moment the hair dies. It is the moment the replacement arrives — about 100 days later.

This is where the seasonal pattern comes in. The most cited evidence is a Swiss study by Kunz, Seifert and Trüeb, published in Dermatology in 2009, which analysed trichograms from 823 healthy women over six years. The analysis showed an annual periodicity in hair growth and shedding, with the highest proportion of telogen hairs in summer, a second and less pronounced peak in spring, and the lowest telogen rates in late winter.

Follow the arithmetic. If the largest wave of hairs enters the resting phase in June and July, and the resting phase runs about three months, those hairs are released in September and October. Spring’s smaller peak produces a smaller echo in early summer.

Search behaviour confirms that this is when people notice. A 2018 time-series analysis of Google Trends data published in the British Journal of Dermatology found that interest in hair loss follows a consistent annual rhythm rather than a random one — and other work has reported increased shedding around August and September in different populations, suggesting the pattern is not limited to one ethnic group.

So the two things Italians and Europeans search for — hair loss in June and July and hair loss in September — are not two problems. They are the beginning and the end of the same cycle.

What summer actually does to your hair

Seasonality explains the timing. It does not explain everything. Summer stacks several additional pressures on the hair cycle, and it helps to separate the ones that cause shedding from the ones that cause breakage — because they look similar in the sink and mean entirely different things.

Factors that push hairs into the resting phase (real shedding)

• UV exposure and heat. Prolonged sun on an uncovered scalp is a physiological stressor. One long-standing hypothesis is that humans retain a vestigial version of the seasonal moult seen in other mammals: more hair is held through the summer as UV protection, then released when the photoperiod shortens.
• Rapid weight loss and restrictive diets. The pre-holiday diet is one of the most common and most underestimated triggers. Caloric restriction and low protein intake are classic causes of telogen shedding, and the effect appears months after the diet, not during it.
• Illness, high fever, and medication changes. Any significant systemic stress — including a fever above 39°C, surgery, or a new drug — can push a large cohort of follicles into telogen at once.
• Psychological stress. Yes, stress-related hair loss is real, and the delay is the reason people miss the connection. A stressful June shows up as shedding in September, by which point the stressor has usually passed and no longer feels relevant.

Factors that damage the hair shaft (breakage, not shedding)

• Sea salt, chlorine, and repeated wet-dry cycles raise the cuticle and make the fibre brittle.
• Heat styling on sun-damaged hair compounds the effect.
• Tight styles worn all summer create mechanical tension at the root.

How to tell them apart in ten seconds: pick up a fallen hair and look at the end that was attached to your scalp. A shed telogen hair has a small, pale, solid bulb — a tiny club shape. A broken hair has no bulb; both ends look the same, and the hair is usually shorter than your full length. Bulbs mean shedding. No bulbs mean damage, and damage is a haircare problem, not a follicle problem.

How much shedding is normal?

The standard figure is 50 to 100 hairs per day, and it is a useful anchor as long as you understand two things about it.

First, that number is not distributed evenly. You do not lose 12 hairs at breakfast. Most telogen hairs are already detached and are simply waiting to be dislodged, so they arrive in bulk when you wash or brush. A wash-day count is a cumulative count, not a daily one. If you wash twice a week, seeing 200 hairs in the shower is arithmetically unremarkable.

Second, perception is unreliable. Long hair looks like more hair. A dark bathroom floor looks like more hair. And once you are worried, you start looking — which alone doubles the number you notice.

A 7-day count that actually means something

Do this before you buy anything or change anything:

1. Pick a normal week. No new products, no change in washing frequency.
2. Every day, collect the hairs you find — brush, pillow, shower drain, hands — into one envelope per day.
3. On wash days, count the shower hairs separately and note them.
4. At the end of the week, divide the total by seven.

An average consistently above roughly 100 per day, sustained for more than a few weeks, is a real signal worth taking to a doctor. The International Society of Hair Restoration Surgery describes a related clinical marker for acute telogen effluvium: diffuse thinning, a more visible scalp, and the collection of more than 100 shed hairs after five days without shampooing.

The count is also your defence against the opposite error — three months of anxiety over a number that turns out to be entirely normal.

Seasonal shedding, telogen effluvium, or pattern hair loss?

Three different things produce “my hair is falling out.” They require three different responses.

The trap is that these overlap. Seasonal shedding sitting on top of early pattern hair loss is extremely common, and it is exactly the scenario in which the seasonal explanation becomes dangerous — because it is partly true, and being partly true makes it convincing enough to ignore the rest.

Five signs it is not just the season

1. It is still happening in December

Seasonal shedding is self-limiting. It builds through September, peaks, and eases through October and November. If shedding follows a seasonal peak and decreases within two to three months, that is generally reassuring; if it continues, worsens, or comes with other symptoms, another cause is likely involved. Put a date in your calendar: 30 November. If nothing has improved by then, this is not the calendar.

2. The loss has a shape

This is the single most important sign. Seasonal shedding and telogen effluvium are diffuse — they thin everything, everywhere, more or less evenly. Androgenetic alopecia is patterned. If your temples are receding, your crown is showing through under overhead light, or your parting is measurably wider than it was last year, the pattern is doing the talking, and the season is a coincidence.

3. The regrowth is thinner than what fell out

Look at the short new hairs at your hairline. In seasonal shedding, the replacements come back with the same calibre as the hairs they replace. In pattern hair loss, each cycle produces a hair that is finer, shorter, and lighter in colour than the last — miniaturisation. Wispy, baby-fine regrowth in a receding zone is not recovery. It is the mechanism of the condition.

4. The year-on-year photograph disagrees with you

Find a photo of yourself from last summer, in daylight, from the same angle. Density is almost impossible to judge in the mirror day to day, and very easy to judge across twelve months. Photographs are also the only objective baseline you will have if you eventually consult a specialist.

5. There are scalp symptoms, or the loss is patchy

Persistent itching, burning, redness, scaling, tenderness, or round bald patches with clean edges are not seasonal and not androgenetic. These point towards inflammatory, autoimmune, or scarring alopecias, where early diagnosis genuinely changes the outcome. This category does not wait for November — see a dermatologist now.

One additional risk multiplier: family history combined with age. Visible thinning before 30 in someone with a family history of baldness tends to progress further and faster. The seasonal explanation is least reliable exactly in the group most inclined to believe it.

What to do in September: a six-week plan

Most of the money spent on hair in September is spent in the first ten days, out of panic, on products chosen at random. Do this instead.

Weeks 1–2 — Measure before you medicate.
Run the 7-day count. Take four baseline photographs — front, both temples, crown from above — in daylight, on the same day of the week, with dry, unstyled hair. Write down anything from the previous 3–6 months that could be a trigger: illness, fever, surgery, a diet, a new medication, a period of heavy stress.

Weeks 2–3 — Correct what is genuinely correctable.
Ask your doctor whether blood tests are appropriate. The panel usually discussed for diffuse shedding includes full blood count, ferritin, TSH with thyroid function, and vitamin D, sometimes with B12 and zinc. Be aware that the evidence here is more debated than supplement marketing suggests: a controlled study of 90 women with chronic telogen effluvium found no significant difference from controls in haemoglobin, ferritin, vitamin B12, vitamin D, copper, biotin, or thyroid function results. Testing exists to find a real deficiency worth correcting — not to justify a supplement stack.

On that note: biotin does nothing for hair unless you are actually deficient, which is rare in people eating a normal diet. Fixing a genuinely low ferritin is worth doing. Taking eight supplements because a shampoo advert suggested it is not.

Weeks 3–4 — Stop making it worse.
Washing does not cause hair loss, and washing less does not save hair — it only concentrates the same shedding into fewer, more alarming events. Wash normally with a gentle shampoo. Reduce heat styling and tight styles for a few weeks while the summer-damaged shaft recovers. Do not start and abandon three different treatments in a month; nothing in hair biology gives a verdict in under three months.

Weeks 4–6 — Decide whether this needs a doctor.
If the count is normalising and the photographs look stable, you have your answer and it cost you nothing. If the pattern signs above are present, book a proper assessment — dermatologist or hair restoration surgeon — with your photographs and your count in hand. For confirmed androgenetic alopecia there are established medical treatments, including topical minoxidil and, for men, oral finasteride. These are prescription decisions with real considerations and side-effect profiles; they belong to a doctor who has examined you, not to a forum.