Seasonal Hair Shedding
A: Yes, seasonal hair shedding is a well-documented phenomenon supported by clinical research, though the evolutionary reasons behind it are still being studied. While many people notice that they seem to shed more hair at certain times of the year, peak hair loss typically occurs in late summer and early autumn, rather than spring or early summer.
Studies show that changing seasons influence the hair growth cycle, particularly through varying levels of daylight. Sunlight exposure fluctuates throughout the year, impacting hormone production. This includes melatonin and vitamin D receptors in the scalp, which play an important role in regulating biological rhythms and hair follicle activity.
During the peak daylight hours of midsummer, a higher percentage of hair follicles enter the resting phase (telogen). Because the resting phase lasts about 100 days, these resting hairs naturally fall out several weeks later, leading to noticeably increased shedding in late summer and autumn.
Researchers believe this pattern may be an evolutionary adaptation: retaining a denser coat of hair in midsummer helps shield the scalp from intense UV radiation, which is then shed once temperatures and daylight levels drop.
Seasonal shedding does not affect everyone in the exact same way. The degree to which these fluctuations manifest is influenced by genetics, geography, and individual physiology. People living closer to the equator experience less pronounced seasonal fluctuations than those in northern or southern latitudes with dramatic seasonal daylight changes.
Some people notice a mild secondary shedding peak in spring, while others experience temporary increases in shedding at different times of the year. However, seasonal shedding is temporary and diffuse, lasting roughly 4 to 6 weeks before normal hair growth cycles resume.
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See also:
The hair growth cycles
The effects of the weather on your hair
What makes hair break more in the fall and winter?