Why more hair falls out in autumn: what is known

Every year, around September and October, the same conversation comes round: "my hair is falling out like mad". For a long time, this was treated as folk wisdom. Today we know it has a scientific basis: several studies, in men and women and in different countries, show that the human hair cycle varies over the year and that hair loss tends to increase in late summer and autumn.

That does not mean that all October hair loss is harmless. Seasonal shedding is moderate, diffuse and passes on its own in a few weeks. If it is heavy, lasts for months, appears as patches or comes with other signs, there may be another cause behind it, which autumn has only made more visible.

What the studies say

The seasonality of human hair has been studied in three different ways, and all point in the same direction.

Measuring the cycle over the year

In the classic study by Randall and Ebling (1991), in Sheffield (United Kingdom), 14 healthy men were followed for more than a year. The proportion of growing follicles (anagen phase) was highest in March, above 90%, and fell progressively to a low in September. Hair loss was greatest between August and September, at about 60 hairs a day, more than double the previous winter.

Examining the scalps of many women

In Switzerland, Kunz, Seifert and Trüeb (2009) analysed, over six years, the trichograms of 823 healthy women complaining of hair loss. The percentage of hairs in the resting phase (telogen phase) was highest in July, with a second, smaller peak in April, and lowest in February. The pattern repeated regardless of age and year. Because resting hairs fall about two to three months later, a peak of telogen hairs in July translates into more hair loss between September and October.

See what people are searching for

Hsiang and colleagues (Hsiang et al., 2018) analysed Google searches for "hair loss" between 2004 and 2016 in eight countries in both hemispheres. In all of them, summer and autumn were associated with more searches. The fact that the pattern reverses with the hemisphere reinforces that it is the season, not the calendar month, that counts.

What these studies do not say

These are studies with limitations: small samples (in the Sheffield case), people who were already complaining of hair loss (in the Swiss case) or indirect data (internet searches). They show a consistent pattern, but the magnitude varies greatly from person to person. Many people notice no difference at all.

Why it happens

There is no definitive explanation, but there are several well-founded hypotheses.

Day length (photoperiod)

In mammals, moulting is regulated by day length, through melatonin and prolactin. Sheep, horses and dogs moult in well-defined seasonal cycles. Humans have lost much of this mechanism, but follicles have melatonin and prolactin receptors and seem to retain an "echo" of this regulation. The longer days of summer would be the signal that leads more follicles to enter the resting phase.

Protecting the scalp in summer

An evolutionary hypothesis suggests that having more hair in summer would protect the scalp from solar radiation. Follicles would hold on to hairs for longer during the summer and release them afterwards, when radiation decreases. It is a plausible explanation, but hard to prove.

Summer itself

Besides the biological clock, summer brings factors that can add up: sun, chlorine, salt and heat damage the hair shaft and make hairs more brittle; holidays with different routines, sleep and diet; summer diets. These factors do not explain the seasonal pattern (which exists in people who work indoors), but may make it more visible. See Hair after summer: how to recover it.

The September "return"

The end of the holidays, the return to work and school and the change of routine are, for many people, a period of stress. An episode of intense stress can trigger a telogen effluvium, which is noticed two to three months later. On this, see Stress and hair loss: what is known.

Seasonal shedding or hair loss that deserves attention?

How much hair is normal to lose?

The most-quoted figure is 50 to 100 hairs a day, but it is an estimate and varies greatly. It depends on hair density, length (long hair looks like "more") and how often you wash: someone who washes their hair twice a week sees, on wash day, the hairs accumulated over several days. More important than counting hairs is noticing a clear change from what is usual for you.

How to tell the difference

Autumn may reveal another problem

An early androgenetic alopecia, an iron deficiency or a thyroid change can go unnoticed for months. When seasonal shedding is added, the hair suddenly seems thinner and the person finally decides to seek help. It is not autumn that causes the problem, but it may be the moment it becomes visible. If this year's hair loss seems different from that of previous years, that is a good reason to get assessed. See also Female hair loss and Hair loss: why it happens and what to do.

What to do in autumn

Seasonal shedding does not need treatment: the follicles releasing the hair are already producing a new one. What you can do is not add other causes and look after the hair that remains.

What helps

• Stay calm and keep to your routine. Wash your hair as often as usual. Washing does not make hair fall out that was not going to fall.
• Eat a varied and sufficient diet, with protein at every meal and sources of iron. Suggestions in Autumn eating for hair.
• Trim the ends damaged by summer, to reduce breakage that is mistaken for hair loss.
• Treat your hair gently: conditioner, wide-toothed comb, hairdryer at a moderate temperature.
• Photograph your parting once a month, in the same light, to compare objectively.
• Look after your sleep and stress when returning to routine.

What is not worth doing

• Buying "anti-hair-loss" supplements without a confirmed deficiency. The evidence shows a benefit only in those who are deficient, and some, in excess, cause hair loss.
• Ampoules and shampoos that promise to "stop seasonal shedding". Seasonal shedding is the natural end of a cycle and there is no solid evidence that these products change it.
• Stopping washing or combing your hair out of fear.
• Starting restrictive diets, which can add a telogen effluvium.

When you should ask for an assessment

At Luxmed, the Hair Medicine consultation includes a clinical history, examination of the scalp and trichoscopy, which shows the proportion of thin hairs and signs of miniaturisation and inflammation. This is how seasonal shedding is distinguished from an alopecia that deserves follow-up. When indicated, we request blood tests.

This article is for information purposes and does not replace a medical consultation. The results of any treatment vary from person to person.

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