Shedding More Hair in Late Summer and Fall?What Studies Show

Every hair on your scalp runs on its own cycle: a long growing phase, then a resting phase, then it falls out and a new one starts. Several studies have found that this cycle tilts with the seasons, so more hairs rest, and then fall, around the same time each year.

The study of women

Swiss dermatologists looked back over 6 years at 823 healthy women who came in worried about hair loss.¹ Women with a disease or a medicine known to cause shedding were left out, and each had a sample of hairs checked under a microscope to count how many were in the resting phase.¹

• Resting hairs peaked in summer.¹
• A smaller peak seemed to appear in spring.¹
• Resting hairs were lowest in late winter.¹

Two long studies of men

The patterns in men point the same way.

Study	What it found
14 men in Sheffield, England, checked every 28 days for 18 months	Growing hairs peaked in March and fell to a low in September.2 Shed hairs peaked around August and September, at about 60 a day, more than double the winter rate.2
10 men in France, photographed for 8 to 14 years	Resting hairs peaked at the end of summer and start of autumn.3 Some men had two peaks a year, and men with very few resting hairs showed no pattern.3

These are small studies, the men’s studies didn’t include women, and the French study came from a hair-care company’s lab.³ But three groups, using different methods, found a similar late-summer rise.

What this means for your drain

In the Sheffield study, shed hairs peaked in August and September, when the fewest hairs were growing.² So more hair in the brush in late summer and fall fits the research. If that happens to you around the same time each year, and settles on its own, a seasonal pattern is a reasonable explanation.

For scale, US dermatologists say shedding 50 to 100 hairs a day is normal.⁴ Excessive shedding usually follows a trigger by a few months, such as:⁴

• Giving birth, a high fever, an operation or an illness
• Losing 20 pounds or more
• Heavy, ongoing stress
• Stopping the pill

After that kind of shed, hair usually regains its normal fullness within 6 to 9 months.⁴ See shedding after COVID or a fever and shedding for more than 6 months.

When it isn’t the season

Get it checked if you notice:

• A wider part or more scalp showing on top. See female pattern hair loss after 50.
• Bald patches, broken hairs or a sore, itchy or scaly scalp.
• Shedding that doesn’t settle after several months.

Try: “My hair seems to shed more every autumn, but this year it hasn’t settled and my part looks wider. Could we check my iron and thyroid and look at my scalp?”

Hair, Everywhere covers normal shedding in Chapter 5, “The Shed,” in a section called “The Hundred-Hair Line.” Its Hair Log keeps the same monthly photos of your part and hairline with dates, so a yearly rise and fall shows up as a pattern rather than a scare. See the book.