Chronic circadian misalignment is a risk factor for hair growth impairment

To identify environmental factors that accelerate hair loss, we focused on modern artificial and aberrant light environments which cause circadian dysfunction. We examined the effect of aberrant light environments on hair growth by exposing mice to repetitive light-dark reversal at three-day intervals, inducing chronic circadian misalignment. Dorsal hair-sheared male mice showed impaired hair growth under this light condition. In addition, synchronization of hair growth cycling by dorsal depilation in male and female mice revealed that this light condition caused a decrease in hair growth rate during anagen. Furthermore, a decrease in hair growth rate was confirmed in male mice by ex vivo culture of whisker hair follicles classified as in anagen. These lines of evidence indicate that artificial and aberrant light environments or chronic circadian misalignment cause impaired hair growth due to a decrease in hair growth rate during anagen and are therefore a potential risk factor for hair loss.