Increased hair fall when the weather warms is a common experience. A temporary increase in hair shedding, known as seasonal effluvium, is a recognized biological pattern. This phenomenon is distinct from persistent hair loss, or alopecia, which involves a failure to regrow hair. Understanding the natural process of hair renewal helps explain why seasonal changes can lead to a temporary increase in shedding.
Understanding the Hair Growth Cycle
Hair growth operates on a continuous, four-stage cycle that runs independently in each follicle. The first phase, Anagen, is the active growth period, which can last anywhere from two to seven years. This phase typically contains 85 to 90 percent of scalp hairs at any time. During Anagen, hair root cells divide rapidly, adding length to the strand.
Following the Anagen phase is Catagen, a brief transition period lasting about two to three weeks, where the hair follicle shrinks and growth stops. The hair then enters the Telogen phase, a resting period for the follicle lasting approximately three months. Around 10 to 15 percent of hairs are in this resting stage at any given moment.
The final stage is Exogen, often considered part of Telogen, where the old hair is released and falls out. This makes way for a new Anagen hair to emerge from the same follicle. A person normally loses between 50 and 100 hairs daily as part of this renewal process. Seasonal shedding occurs when a higher percentage of follicles synchronize and enter the Telogen/Exogen phases simultaneously.
Biological Triggers for Summer Shedding
The increase in shedding observed in late summer and early autumn is a delayed reaction to environmental changes experienced months earlier. Scientific studies suggest that hair follicles are pushed into the resting (Telogen) phase during the height of summer, specifically in July. This leads to a mass shedding event approximately two to three months later, causing the noticeable increase in hair fall around September or October.
This timing is supported by an evolutionary hypothesis suggesting the body retains more hair during summer to provide a denser protective layer against intense ultraviolet (UV) radiation. To prepare, a greater proportion of follicles prematurely enter the Telogen phase in June or July. The body’s response to increased daylight and heat serves as the environmental cue for this cycle shift, potentially mediated by hormonal fluctuations like melatonin.
The sun’s UV radiation can also act as a physiological stressor on the scalp, contributing to the premature transition of hairs into the resting phase. This temporary condition is classified as acute telogen effluvium, a diffuse shedding triggered by an identifiable physiological event or stress. Since the Telogen phase lasts around 100 days, the impact of the summer stressor is observed as increased hair loss toward the end of the season or at the start of fall.
Distinguishing Normal Shedding From Underlying Hair Loss
It is important to differentiate between temporary seasonal shedding and persistent forms of hair loss. Normal seasonal shedding is a form of telogen effluvium characterized by a temporary, diffuse increase in lost hairs. It does not lead to noticeable bald patches or significant changes in overall hair density. The shedding is self-correcting and usually lasts for about four to eight weeks before the cycle normalizes.
Signs that hair loss may signal an underlying health issue include persistent, non-seasonal thinning lasting longer than a few months or the appearance of visible bald patches. Other warning signs are a sudden, severe loss of volume, hair breakage accompanied by scalp irritation, or a widening of the part line. If the increased shedding is accompanied by symptoms like burning, itching, or inflammation of the scalp, a medical consultation is warranted.
Non-seasonal hair loss, or alopecia, can stem from various internal factors that disrupt the hair cycle. These factors include thyroid disorders, iron or zinc deficiencies, or significant emotional or physical stress. A dermatologist or trichologist can perform an examination to determine if the issue is a benign seasonal adjustment or a condition requiring medical intervention.
Practical Tips for Managing Seasonal Shedding
While the biological shift is unavoidable, several simple practices can help minimize the appearance and severity of temporary seasonal shedding. Adopting gentle hair care habits is beneficial. This includes avoiding tight hairstyles like ponytails or braids that place continuous tension on the hair roots. It is also helpful to minimize the use of high-heat styling tools, which cause mechanical stress and increase breakage.
Supporting the hair cycle through nutrition is an effective strategy to promote healthy regrowth. Ensuring a diet rich in protein, the building block of hair, provides necessary resources for the follicles. Adequate intake of nutrients like iron, zinc, and B vitamins such as biotin is also important. Staying well-hydrated supports overall hair and scalp health.
Maintaining a healthy scalp environment can further encourage the new growth phase. Gently massaging the scalp for a few minutes daily helps stimulate blood circulation, which delivers oxygen and nutrients to the hair follicles. Using a mild, nourishing shampoo and conditioner helps keep the scalp clean and the hair strands resilient during the temporary shedding period.