Seasonal Shedding in Autumn: Why the Drain Fills Up Every October
Every October, the same question fills hair forums: is this normal, or is something wrong? The drain has more hair in it, the brush fills faster, and the part looks wider. The answer is usually normal, and the reason is a clock the scalp keeps without telling you. The hairs you shed in autumn entered their resting phase in summer, and the shedding you see now is the bill coming due about 100 days later.
The studies that established this are old and careful. Kunz, Seifert, and Trueb, in a 2009 paper in Dermatology, followed 823 women with trichograms over six years and found the telogen proportion, the share of hairs in the resting phase, highest in July and lowest near February. Hairs entering telogen in July shed about 100 days later, in autumn. Randall and Ebling, in a 1991 study in the British Journal of Dermatology, followed 14 healthy men in Sheffield for 18 months and found anagen, the growth phase, above 90 percent in March and lowest in September, with shed hairs peaking in August and September at about 60 a day, more than twice the winter rate. Courtois and colleagues, in 1996, followed 10 men for 8 to 14 years and found telogen highest at the end of summer and the beginning of autumn. Liu and colleagues, in 2014, found the same pattern in 41 Chinese volunteers: telogen highest around September, lowest in January.
The photoperiod explanation
The leading explanation is photoperiod, the length of daylight. Hair follicles, like the coats of other mammals, respond to the seasonal light cycle, and the mechanism is thought to involve melatonin and prolactin, though the mechanism in humans is not fully proven. The pattern is consistent across climates and sexes, which is the part that makes it believable: the same autumn peak shows up in British men, Swiss women, and Chinese volunteers, and the same 100-day lag shows up between the telogen peak and the shed.
Normal shedding is 50 to 100 hairs a day, according to the American Academy of Dermatology, and a seasonal shed can push that higher for a few weeks without meaning anything is wrong. The shed settles in roughly 8 to 12 weeks, as the follicles that entered telogen in summer finish shedding and the new anagen hairs begin to replace them. The hair that falls out in October was already scheduled to fall out in July. You are not losing it because of something you did last week.
When it is not seasonal
The line between seasonal and pathological is time and pattern. A seasonal shed settles in about two months. Telogen effluvium, the acute shock shedding that follows illness, high fever, rapid weight loss, childbirth, or severe stress, can push up to 30 to 50 percent of anagen hairs into telogen and becomes noticeable roughly two to three months after the trigger. If the shedding is still going strong at three months, if it is patchy rather than diffuse, or if the scalp is visible in a way it was not before, that is not the season. That is a reason to see a dermatologist, and to check ferritin and thyroid, because both are common, treatable causes of a shed that will not stop.
Keep reading: Telogen Effluvium: The Shedding That Starts Two Months After the Illness, Scalp Buildup: Clarifying Shampoo or Scalp Exfoliation?, and Silk Pillowcases and Hair: The Friction Numbers, Without the Hype cover the nearby cases in this series.
Frequently asked questions
Is seasonal shedding in autumn normal?
Yes. Studies show telogen, the resting phase, peaks in July and the hairs shed about 100 days later, in autumn. Shed hairs peaked at about 60 a day in August and September in one study, more than twice the winter rate.
How long does seasonal shedding last?
Roughly 8 to 12 weeks. The follicles that entered telogen in summer finish shedding, and new growth replaces them. If it is still going strong at three months, it is not seasonal.
Why do I shed more hair in autumn than in winter?
The telogen proportion is highest in late summer and lowest near February. The hairs that entered the resting phase in July shed about 100 days later, in autumn, which is why the drain fills up in October.
When should I worry about autumn shedding?
If it lasts more than three months, if it is patchy rather than diffuse, or if the scalp is newly visible. Those point to telogen effluvium, iron deficiency, or a thyroid issue, not the season.