The sight of extra hair on a pillow or in a shower drain often sparks concern about hair loss. This common experience leads many to wonder if humans, like other mammals, have a specific “shedding season.” Seeing hair fall out is usually part of a normal, continuous biological process known as hair shedding. This natural fluctuation, medically termed telogen, is distinct from true hair loss, which involves an underlying medical condition preventing hair from regrowing. Scientific observation supports the belief that a seasonal pattern of hair fall exists.
The Biology of Hair Shedding
The appearance of shed hair is the final step in the multi-stage hair growth cycle. Each hair follicle operates independently, ensuring that hair loss is staggered and continuous throughout life.
The cycle begins with the Anagen phase, the long growth period where hair is actively produced. This phase is the longest, typically lasting between two and eight years, and at any given moment, 85 to 90% of scalp hairs are in this active state. Its duration is determined by genetics and dictates the maximum length hair can grow.
Following the growth period is the Catagen phase, a short transitional stage lasting only about two to six weeks. The hair follicle shrinks and detaches from its blood supply, signaling the end of active growth. The hair strand formed becomes a “club hair” that remains anchored in the scalp but is no longer growing.
The final stage is the Telogen phase, the resting period that lasts for two to four months. The hair follicle is dormant, and the club hair sits in the follicle until a new hair beginning the Anagen phase pushes it out. This natural release is the shedding people notice; about 10 to 15% of all hairs are in this resting stage at any time.
Identifying the Seasonal Pattern
While shedding occurs daily, scientific studies suggest the rate at which follicles enter the resting phase is influenced by the seasons. Research indicates that a higher proportion of hair follicles enter the Telogen phase during the late summer months, preparing the hair for its eventual release.
Because the Telogen phase lasts approximately 100 days, the increased number of resting hairs in August and September leads to a noticeable surge in shedding two to three months later. This results in the peak “shedding season” occurring most prominently during the Autumn months of October and November.
One prominent theory suggests this seasonal fluctuation may be an evolutionary remnant, linking human hair cycles to those observed in other mammals. It is hypothesized that the increased hair retention during summer protected the scalp from intense solar radiation and UV exposure. When the summer months end, this protective layer is no longer necessary, and the follicles transition into the resting phase.
Environmental factors, such as hormonal shifts triggered by changes in daylight, are also potential triggers for this seasonal synchronization. Studies consistently observe this seasonal rhythm, particularly in the Northern Hemisphere. Since this shedding is temporary, it does not result in permanent thinning, and the follicles quickly re-enter the growth cycle.
Differentiating Normal Shedding from Hair Loss
Normal daily shedding is between 50 and 100 hairs, a small fraction of the 100,000 or more hairs on a typical scalp. Even if shedding increases temporarily during the seasonal peak, it often remains within the range of normal fluctuation. However, daily hair fall exceeding 150 hairs for an extended period can signal excessive shedding or true hair loss.
Excessive hair shedding, known as Telogen Effluvium, is temporary. It typically occurs two to three months after a physical or emotional stressor, such as high fever, childbirth, or severe stress. This condition causes sudden, diffuse thinning across the entire scalp, but the hair follicles remain capable of producing new hair. Telogen Effluvium usually resolves once the underlying trigger is addressed.
In contrast, true hair loss, or Alopecia, is often chronic and progressive, involving the gradual miniaturization of the hair follicle. The most common form, Androgenetic Alopecia, or patterned hair loss, is driven by genetics and hormones. It presents as a receding hairline or thinning at the crown in men and a widening part in women. This condition will not resolve without intervention because the follicles are permanently affected.
A person should consult a healthcare provider, such as a dermatologist, if the shedding is accompanied by:
- Visible bald patches.
- An unusual change in the hairline.
- Excessive hair fall lasting longer than six to nine months.
- Scalp pain, itching, or inflammation.
Distinguishing the quantity, pattern, and duration of hair loss is necessary for accurate diagnosis and appropriate treatment.