Seasonal hair shedding is a real phenomenon that many people notice but few understand — the predictable increase in hair shedding in autumn that resolves by winter, or the dryness-related scalp changes in cold weather. Understanding the relationship between climate and hair loss separates genuine concerns from normal seasonal variation.
Seasonal telogen effluvium: studies have documented a peak in telogen hair count (proportion of hairs in the resting phase) in late summer and autumn. This corresponds to a shedding peak in autumn — more hairs in the brush, more visible shedding in the shower. The mechanism is thought to relate to photoperiod — changes in day length that affect follicle cycling. This is normal, self-resolving variation, not a sign of progressive hair loss.
Cold weather and scalp dryness: cold, dry air reduces scalp skin hydration. A drier scalp can appear to shed more because dry skin flakes make individual shed hairs more visible. The scalp also produces more sebum in colder conditions as a compensatory response, which can worsen seborrhoeic dermatitis in susceptible individuals — and scalp inflammation exacerbates shedding.
Sun exposure: prolonged intense UV exposure damages the hair shaft, making existing hair more brittle and prone to breakage. This is not true hair loss (the follicle is unaffected) but the cosmetic effect of breakage — shorter, thinner-looking hair — can mimic hair loss. UV-protective leave-in conditioners and wearing a hat in intense sun reduce this.
Heat and humidity: hot, humid conditions increase scalp sweating which can worsen dandruff and folliculitis in susceptible individuals. Neither temperature nor humidity affects androgenetic hair loss progression.
Related reading
