Many people notice increased hair shedding during warmer months, prompting questions about summer’s impact on hair loss. Understanding the underlying biological processes can clarify if this phenomenon is a normal seasonal adjustment or a cause for concern.
Understanding the Hair Growth Cycle
Human hair undergoes a continuous cycle of growth and rest. This cycle consists of three primary phases: anagen, catagen, and telogen. The anagen phase is the active growth period, lasting two to seven years, during which hair follicles produce new cells.
Following anagen, the catagen phase is a brief transitional stage, lasting a few weeks, where hair growth slows and the hair follicle detaches from its blood supply. The final phase is telogen, a resting period of three months, after which old hair is shed, making way for new growth. Each hair follicle operates independently, meaning hair is constantly in different stages of this cycle, preventing all hair from falling out simultaneously.
The Reality of Seasonal Hair Shedding
Increased hair shedding in summer is a recognized seasonal pattern, supported by scientific observations. This phenomenon is often described as seasonal telogen effluvium, a temporary condition where more hair follicles prematurely enter the resting (telogen) phase. Studies indicate that hair shedding tends to peak in late summer or early autumn, often around August or September. Conversely, the lowest rates of hair loss are observed in the spring.
A study analyzing Google searches for “hair loss” across eight countries found search interest consistently spiked in the summer and fall, aligning with reported seasonal shedding patterns. While normal daily shedding is around 50 to 100 hairs, seasonal changes can temporarily increase this number. This increased shedding is usually diffuse, affecting the entire scalp, and tends to resolve within a few weeks to a couple of months.
Biological Factors Behind Summer Shedding
Several biological mechanisms explain why increased hair shedding occurs seasonally, particularly in late summer. One theory suggests an evolutionary adaptation: humans may retain more hair in summer to protect the scalp from UV radiation, shedding it later when the need diminishes. Increased daylight exposure in summer also influences the hair growth cycle.
Hormonal fluctuations are another factor; changes in daylight and temperature can affect hormone levels like melatonin, which regulates hair growth cycles. Increased sun exposure in summer can also trigger more hair follicles to enter the resting phase prematurely, leading to increased shedding in subsequent months. Environmental factors like high temperatures and humidity can also weaken hair and disrupt the scalp, potentially contributing to shedding.
When to Seek Professional Advice
While seasonal hair shedding is a temporary and normal physiological response, it is important to distinguish it from more persistent or concerning forms of hair loss. Excessive or sudden hair loss, such as hair coming out in large clumps or leading to noticeable thinning, can signal an underlying issue. Patchy hair loss, a rapidly receding hairline, or bald spots are indicators that warrant professional attention.
Other signs to consult a healthcare professional include persistent thinning beyond seasonal changes, or if hair loss is accompanied by scalp irritation, redness, or pain. A dermatologist can help determine the cause of hair loss, differentiating between normal shedding and conditions like telogen effluvium or other forms of alopecia, and recommend appropriate treatment.