Comment on Seasonal Hair Shedding

Telogen effluvium (TE) has gained particular interest since the original report of Sulzberger et al . on an unexplained apparent increase in the incidence of diffuse alopecia in women in 1960. Headington’s classification of TE represents the most rational of all proposals and has proven its validity, both for the understanding of the pathologic dynamics underlying TE and in clinical practice, covering all clinical types of TE. In delayed telogen release, hair follicles remain in prolonged telogen rather than being shed and recycled into anagen; when finally teloptosis sets in, the clinical sign of increased shedding of telogen hair is observed. This process underlies molting in mammals. It is likely that environmental factors, such as the photoperiod, mediate through the optic pathway and the neuroendocrine system hair coat phenotype and function to photoperiod-dependent environmental changes. The fact that human hair follicles, just as those of other mammals, undergo cyclical activity implies that human hair is affected by these phenomena. Seasonal hair shedding has so far found surprisingly little attention, and yet has a significant impact on our understanding of TE and clinical management of women complaining of hair loss. The existence of seasonal fluctuations in hair growth and shedding complicates the assessment of pharmacological effects of hair growth-promoting agents, both in clinical practice and in efficacy studies. Awareness of these fluctuations is a prerequisite to providing the correct cause and prognosis to the patient, ensuring patient compliance with therapy, but it also has potentially serious implications for investigations with hair growth-promoting agents.