After exclusion of patients with a disease or on drugs known to cause hair loss, 823 women remained. Analysis of trichograms demonstrated annual periodicity in the growth and shedding of hair, manifested by a maximal proportion of telogen hairs in summer. A second peak seems to exist, though it is less pronounced, in spring. The telogen rates were lowest in late winter
Seasonality of Hair Shedding in Healthy Women Complaining of Hair Loss
Michael Kunz, Burkhardt Seifert, Ralph M. Trüeb https://www.zora.uzh.ch/id/eprint/20699/1/216832.pdf