Hair shedding is seasonal; many people experience a temporary, mild increase in the number of hairs they shed at certain times of the year. This phenomenon is a recognized fluctuation in the natural process of hair turnover, which typically sees an individual lose between 50 and 100 strands daily. While the sudden appearance of extra hair can be concerning, this temporary increase usually represents a slight synchronization of the body’s natural cycles. For most individuals, this seasonal shedding is a self-correcting physiological response to environmental shifts that does not lead to visible, long-term thinning of the hair density.
The Biological Mechanism Behind Seasonal Shedding
The underlying cause of seasonal shedding rests within the three main phases of the hair growth cycle. The Anagen phase is the active growth period, followed by the Catagen phase, a short transitional period where growth stops. The Telogen phase is the resting stage, typically lasting two to six months, after which the hair strand is released, and a new hair begins to grow in the follicle.
Scientific research suggests that seasonal changes, particularly shifts in the length of daylight, act as an environmental signal to the hair follicles. An evolutionary hypothesis proposes that a denser head of hair is maintained throughout the summer to protect the scalp from intense ultraviolet radiation. To achieve this, a larger proportion of hair follicles are signaled to enter the Telogen phase simultaneously during the late spring and early summer months.
This synchronized entry into the resting phase creates a delayed effect on shedding. Since the Telogen phase lasts approximately three months, the noticeable increase in hair fall occurs later, as the follicles release the resting hairs all at once. This mechanism ensures that the hair is at its densest during the summer months, reserving the bulk of the shedding for the cooler months.
Identifying Peak Periods and Duration
Studies tracking hair growth patterns consistently identify a peak period for increased shedding. This peak typically occurs in late summer and autumn, often beginning around August and continuing through November. This timing corresponds directly to the two-to-three-month delay that follows the period of maximal sunlight exposure, when the highest number of hairs are signaled to enter the resting phase.
While the primary peak is observed in the fall, a less pronounced secondary peak is sometimes noted during the spring months. The shedding seen during these times is considered normal when it lasts for a limited duration. For most people, seasonal hair shedding should subside on its own within four to eight weeks as the hair follicles reset their growth cycle. A sudden increase in hair fall that occurs annually during these windows is a strong indicator of this natural physiological process.
When to Consult a Professional
While seasonal shedding is a normal biological occurrence, it is important to distinguish it from hair loss that requires medical attention. You should consult a healthcare professional, such as a dermatologist, if the increased shedding persists beyond eight to ten weeks. Shedding that continues for several months is a sign that the underlying cause may be more than just seasonal change.
Signs of Pathological Hair Loss
A clear indicator that the shedding is pathological rather than seasonal is a noticeable reduction in overall hair density or the development of sudden bald patches. Seasonal hair loss is diffuse, meaning it occurs evenly across the entire scalp and does not typically result in visible thinning.
Any accompanying symptoms should also prompt a medical evaluation, as these are not features of normal seasonal turnover:
- Scalp pain
- Itching
- Redness
- Irritation
Common Non-Seasonal Causes
The most common non-seasonal cause of excessive shedding is a condition called Telogen Effluvium, where a significant physical or emotional stressor prematurely pushes a large number of hairs into the shedding phase. Triggers for this condition can include severe illness, major surgery, significant psychological stress, or sudden changes in diet.
Other underlying medical issues, such as thyroid disorders, certain medications, or nutritional deficiencies like low ferritin (stored iron) or Vitamin D, can also cause persistent hair loss. A professional can conduct blood tests and a thorough examination to accurately diagnose the root cause and recommend appropriate treatment.