Seasonal hair shedding: normal or a warning sign?

Is it normal to lose hair every day?

Yes. Each hair grows for several years (the anagen phase), then rests for about three months (the telogen phase) before falling out; a new hair then forms in the same follicle. At any time, about nine hairs in ten are growing.

A figure of 50 to 100 hairs lost per day is often quoted. It is an order of magnitude, not a precise threshold: it depends on how the hairs are counted, and some specialists even consider it too high.

Does seasonal shedding really exist?

Yes, and it has been measured. In England, fourteen healthy men were followed for eighteen months. The share of growing hairs peaked in March, at over 90%, and reached its low point in September. Shedding, for its part, peaked in August and September: about 60 hairs a day, more than double the previous winter.

In Zurich, a six-year study looked at 823 healthy women who had consulted for hair loss. The proportion of resting hairs was highest in summer, with a second, smaller peak in spring, and lowest in late winter. A resting hair falls out in the following weeks or months: hence more hair in the brush in late summer and autumn.

Nobody knows exactly why. Summer sunlight is the explanation most often suggested. These studies are old and small, but other work points in the same direction.

Telogen effluvium: when shedding speeds up

Sometimes, a shock to the body pushes many hairs into the resting phase at the same time. They fall out together, usually two to three months later, sometimes a little more: this is telogen effluvium. This delay explains why people rarely make the link with the cause, often forgotten by the time the shedding starts.

The best-known triggers:

• A high fever, a severe infection or an operation. After COVID-19, shedding began on average about two months later in the studies.
• Childbirth: shedding often begins around the second month and peaks around the fourth.
• A strict diet or major weight loss.
• Severe stress: bereavement, separation, job loss, a loved one's illness.
• Some medicines, or stopping the contraceptive pill.
• A thyroid disorder, or iron deficiency, although this last link is still debated.

Telogen effluvium does not leave bald patches. Once the cause has gone, shedding usually stops within two to six months; volume returns more slowly, often within six to nine months. If the cause persists, however, shedding can go on.

Which signs call for a medical opinion?

Diffuse shedding a few months after an identifiable event, in a healthy person, often needs nothing more than an explanation. A medical opinion is useful, however, if:

• bald patches appear;
• shedding has lasted more than six months: this is called chronic telogen effluvium, which sometimes hides early androgenetic alopecia;
• your parting is widening or your ponytail is getting thinner, which points rather to androgenetic alopecia;
• your scalp is red, flaky, itchy, burning or painful;
• your eyebrows, eyelashes or body hair are falling out too;
• other signs come with the shedding: unusual tiredness, weight change, irregular periods, acne or new hair growth on the face or body;
• or simply if this shedding worries you.

What I look at during the consultation

I start with the history of the shedding: since when, how fast, what happened in the preceding months, medicines, diet, family history.

Then I examine. For the pull test, I take a lock of about fifty hairs and pull gently: if more than one hair in ten comes out, shedding is active. I look closely at the scalp with an illuminated magnifier (dermatoscope), which helps distinguish telogen effluvium from androgenetic alopecia. Standardised photographs serve as a reference for follow-up.

A blood test is not routine. I suggest one when the history or examination points to a cause, or when shedding goes on: for example to check iron stores (ferritin) or the thyroid.

What does not help, and may even get in the way

"Hair" supplements. Without a proven deficiency, no robust study shows that they make hair grow back. Some nutrients can even do harm at high doses: too much vitamin A or selenium can, on its own, cause hair loss.

Biotin (vitamin B7). A true deficiency is rare with a normal diet, and no benefit has been shown without a deficiency. Yet many hair supplements contain high doses, and biotin can distort some blood tests, upwards or downwards, including thyroid tests. The US Food and Drug Administration (FDA) issued a warning in 2017, renewed in 2019, notably about troponin, a test used to diagnose a heart attack. If you take it, say so before any blood test.

If iron deficiency is confirmed, I correct it: this is justified for your health, even though its direct effect on hair is still debated. Beyond that, no treatment has been shown to speed up the end of acute telogen effluvium: the priority is to find the cause, remove it if possible, and then let time do its work.

What about PRP?

At the practice, I offer scalp PRP as an add-on treatment in androgenetic alopecia, when follicles are still present. It has no place in seasonal shedding or temporary telogen effluvium, which resolve on their own. If the examination reveals androgenetic alopecia behind the shedding, we discuss the options together; the article on male pattern baldness describes the treatments for men. Very often, explaining and monitoring is enough.