Hair health · Seasonality
Autumn hair loss: what science says — and what’s actually worth taking
It starts in the shower drain. Then it's the brush, the pillow, the mark on the shoulder of a dark sweater. Every year, around September, thousands of people in Portugal search for the same thing with the same question in mind: is this normal, or is something wrong? In the vast majority of cases, it's normal — and it's temporary. This article explains why, how to distinguish seasonal shedding from shedding that warrants clinical investigation, and what makes sense to do in the coming weeks.
hairs per day is the range considered normal by most clinical sources
is the delay between hair entering resting phase in summer and falling out in early autumn
Is autumn hair loss real?
It's not just an impression or a summer-end myth. It's a measurable pattern, documented for decades in dermatological studies using trichograms and phototrichograms.
A landmark study followed 823 healthy women over six years and demonstrated a clear annual periodicity in hair growth and shedding: the proportion of hairs in the resting phase — called telogen — peaks in summer, with a second smaller peak in spring, and a minimum at the end of winter.
Subsequent work, using phototrichograms in long-term follow-ups, places the highest percentages of telogen in August, September, and October, with minimum values in December, January, and February. A study with nearly 2,900 participants over two consecutive years found the same pattern: more shedding between July and October, less in January.
In other words: the peak of hairs that enter the resting phase is in summer. The peak of hairs that fall out is in late summer and early autumn. That's why September is the month when everyone notices.
A relevant detail from the data: this seasonal variation appears regardless of whether the person already has male or female pattern hair loss. It's a biological rhythm that overlays everything else happening on the scalp.
The four pillars
Why hair falls out three months after summer
Four mechanisms explain almost everything observed in September — and, above all, explain why the phenomenon tends to resolve itself.
The hair follicle cycle
Each follicle goes through three phases: anagen (active growth, between two and six years), catagen (transition, two to three weeks), and telogen (resting, a few months, at the end of which the hair detaches to make way for new hair). At any given moment, some hair is in the resting phase — that's how the system works.
Photoperiodism
The most cited hypothesis for seasonality is the solar shield: the body maintains a greater proportion of hair during the peak of summer, a time of higher radiation on the scalp. It's the same mechanism linked to day length that regulates fur shedding in mammals — an evolutionary echo that continues to function despite central heating.
The three-month lag
Hairs that enter telogen in summer don't fall out immediately. They remain in the resting phase and are only released about three months later, which places the shedding precisely at the transition to autumn. The cause is in summer; the effect appears in September.
The false alarm of wash day
A hair that detaches from the follicle doesn't fall out immediately — it remains tangled in the rest of the hair. Those who wash their hair every two or three days release all these hairs at once in the shower. The tuft seems dramatic, but it corresponds to two or three days of accumulated normal shedding.
This is the reference range — and seasonal shedding is an oscillation, not a new baseline
Some dermatologists work with a broader range, from 50 to 150. Seasonal shedding adds a temporary variation to this baseline for a few weeks. To evaluate progress objectively, it's advisable to always compare equivalent wash days — never a wash day with a day when only brushing occurred.
Practical examples
What to do in the next six weeks
None of these measures stop shedding that is already underway — because, as explained below, that's not biologically possible. What they do is reduce noise and prepare the next growth cycle.
Ferritin
Reflects iron stores. It can be low without the complete blood count indicating anemia — and often goes unnoticed.
25(OH)D
September is when reserves are at their highest point of the year. If the value is already low now, it will be worse in winter.
TSH
Thyroid function is a frequent and often unidentified cause of diffuse hair loss.
Complete blood count
Completes the basic screening and contextualizes the ferritin value. It costs little and changes the conversation.
Less mechanical tension
Less tight ponytails, less aggressive brushing of wet hair, less direct heat.
Sufficient protein
Hair is keratin. In phases of marked caloric restriction, it's the first thing to protect.
Clean scalp
A scalp without flaking or irritation is the ground where new hairs are born.
Photographic record
The same part, the same light, once a week. It's the most honest way to evaluate progress — memory is unreliable.
Seasonal or clinical? How to distinguish
Seasonal hair loss is a form of telogen effluvium — the clinical term for diffuse hair shedding that occurs when an unusual number of follicles enter the resting phase at the same time. The difference between the seasonal version and the version requiring investigation lies in the pattern, duration, and density.
| Seasonal hair loss | Hair loss requiring evaluation | |
|---|---|---|
| Duration | A few weeks; tends to stabilize from October onwards | Several consecutive months, or progressively worsening |
| Pattern | Diffuse — uniform throughout the scalp | Localized — temples, crown, or areas without hair |
| Density | Returns to the same point year after year | The parting widens; the scalp becomes visible |
| Recurrence | Has happened in previous Septembers | First time, or progressively worse |
Medical evaluation is warranted when hair loss is accompanied by persistent fatigue, weight changes, cold intolerance, brittle nails with ridges, very heavy menstrual cycles, or when it occurred two to three months after surgery, infection, childbirth, a very restrictive diet, or a period of intense stress.
Smart supplementation
Why most hair supplements don't solve this
Here's the inconvenient part for supplement sellers. A hair that has already entered telogen is disconnected from the dermal papilla and blood supply. It is biologically pre-programmed to detach. No shampoo, serum, or capsule will re-attach it to the follicle.
The practical consequence is this: if someone starts a hair supplement today and the shedding stops within six weeks, there's no way to know if it was the supplement or the calendar — because that's exactly when seasonal effluvium resolves itself. This is why these products seem to work so well in October and November.
This doesn't mean there's nothing to do. It means that useful intervention isn't stopping current shedding: it's ensuring that the next growth cycle has raw material. Supplements are exactly that — a complement to a varied diet, never a substitute for it or for clinical evaluation.
Three micronutrients have authorized health claims in the European Union specifically for the maintenance of normal hair: zinc, selenium, and biotin. This is an important difference from most hair marketing — it means that the relationship with hair has been evaluated and accepted, not just asserted.
Nutrined
Hairformula 120 Caps
Combines in a single daily dose nutrients with authorized claims for hair — zinc and biotin, which contribute to the maintenance of normal hair — along with B-complex vitamins and cystine, an amino acid present in the keratin structure. For those who prefer a combined approach instead of managing three separate bottles, this is the simplest option to maintain throughout autumn and winter.
View Nutrined's Hairformula →Now Foods
Zinc Glycinate 30 mg
Zinc in the form of chelated bisglycinate, chosen for good digestive tolerance. Zinc contributes to the maintenance of normal hair, the normal functioning of the immune system, and the protection of cells against undesirable oxidation.
View product →Now Foods
Selenium 100 mcg
Selenium in L-selenomethionine, in a discreet daily dose. Selenium contributes to the maintenance of normal hair and the normal functioning of the immune system. Soil in Portugal is relatively poor in this mineral, making dietary intake more variable than supposed.
View product →Now Foods
Iron Complex
Iron combined with vitamin C, folate, and vitamin B12. Iron contributes to the reduction of tiredness and fatigue and to the normal formation of red blood cells and hemoglobin; vitamin C increases iron absorption. It is only advisable when there is a confirmed deficiency in analyses.
View product →Frequently asked questions
The questions that always come up in September
How long does autumn hair loss last?
Typically a few weeks. Trichogram data show that telogen percentages begin to decrease from October and reach their minimum in winter. If it persists for more than three months, it is no longer reasonable to attribute it to the season.
Does seasonal shedding lead to hair thinning?
Not with seasonal shedding. Density returns to the same point year after year. When the parting progressively widens year after year, it is a different type of shedding and warrants dermatological evaluation.
Does biotin cure hair loss?
Biotin contributes to the maintenance of normal hair, but a true biotin deficiency is rare in those with a varied diet. Without a deficiency, supplementing doesn't add anything — and high doses interfere with thyroid tests and cardiac markers.
Does it make sense to take collagen for hair?
Collagen has no authorized health claims in the European Union for hair. Hair is keratin, not collagen. Ensuring total protein intake throughout the day has a more solid basis.
The useful intervention is not to stop the shedding that is already underway. It is to ensure that the next cycle does not find the tank empty.
September is a month when many people panic buy — and October is the month when almost everyone thinks the purchase worked. The calendar is generous with hair products. It is more worthwhile to take advantage of this time of year to do what is rarely done: measure. Ferritin, 25(OH)D, TSH and blood count cost little, take one morning, and transform a diffuse concern into an informed decision. If there is nothing to correct, that's good news. If there is, it was found at the right time — before winter, and in time for the next growth cycle.
Caring for your hair judiciously
- Nutrients with authorized health claims for the maintenance of normal hair: zinc, selenium, and biotin
- Selected brands, with chelated forms and transparent compositions
- Advice from someone who knows the catalogue — and knows when the answer is "get tested first"
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