People commonly notice increased hair shedding during the warmer months, often noticing increased shedding in late summer or early autumn. This phenomenon, known as seasonal shedding, is a documented occurrence that links changes in the environment to the natural biology of the hair follicle. The perception of increased hair loss during this time is generally not a sign of a medical problem but rather a temporary, physiological adjustment by the body. This temporary increase in shedding is rooted in how the hair growth cycle responds to environmental cues like increased daylight and temperature.
The Hair Growth Cycle
Hair growth is not a continuous process, but rather a cyclical one that occurs independently in each follicle across the scalp. This cycle is typically broken down into three main phases that dictate the life of a single hair strand. The first phase is Anagen, the active growth stage, where hair cells divide rapidly and the hair shaft lengthens; approximately 85% of scalp hairs are in this stage and it can last for several years.
Following the Anagen phase is Catagen, a short transitional period lasting only a few weeks where the hair follicle shrinks and hair growth stops. The final stage is Telogen, the resting phase, which typically lasts around three months and affects about 10-15% of the hair on the scalp. Shedding, or the Exogen phase, is the natural conclusion of the Telogen phase, where the old hair is released from the follicle to make way for a new hair to begin the Anagen phase.
The Science Behind Summer Shedding
The underlying cause of seasonal hair shedding is a biological mechanism that synchronizes a larger number of hair follicles into the Telogen phase during the summer. The body’s response to increased daylight hours and warmer temperatures shifts more hair into the resting state. This is believed to be an evolutionary holdover, perhaps to provide a denser “coat” of hair during winter for insulation or to reduce hair density in summer for cooling.
An increased number of hairs entering the resting phase in the height of summer means a proportional increase in hairs entering the shedding phase a few months later. Since the Telogen phase lasts approximately three months, the hair follicles that enter the resting state in June and July are ready to be shed in September and October. This time lag explains why the most noticeable increase in shedding occurs not in the middle of summer, but rather in late summer and early autumn. The higher exposure to UV radiation and heat during the summer months is also hypothesized to potentially stress the scalp.
Distinguishing Normal Shedding from Hair Loss
Normal daily shedding involves losing approximately 50 to 100 hairs, which is part of the regular hair cycle and should not cause noticeable thinning. Seasonal shedding temporarily increases this number, but it remains a self-limiting, temporary condition known as telogen effluvium, where the hair follicles are simply cycling faster. This temporary increase in shedding should last no longer than two months before the hair returns to its normal growth pattern.
True hair loss, or alopecia, is different because it involves hair that is prevented from growing back, leading to a reduction in hair density over time. Warning signs that warrant a consultation with a healthcare provider include shedding that continues aggressively for more than eight weeks or the appearance of distinct bald patches. Other concerning signs include a noticeably receding hairline, a widening part, or loss accompanied by burning, itching, or pain on the scalp.
Practical Steps for Management
While seasonal shedding is a temporary biological event, there are simple, practical steps to support the hair and scalp during this time. Focusing on a gentle hair care routine minimizes external stress that could exacerbate the natural shedding process. This includes avoiding tight hairstyles that pull at the root and reducing the use of high-heat styling tools, which can cause breakage.
Internal support through nutrition is also beneficial, as hair is primarily composed of protein and requires specific micronutrients to grow optimally. Ensuring adequate intake of high-quality protein, iron, and zinc helps maintain healthy hair growth cycles. Additionally, B vitamins like biotin, along with vitamins C and D, are known to support the hair follicle and overall hair resilience. Maintaining a healthy scalp environment with mild shampoos and gentle massage can also promote better circulation and support the emerging new hair strands.