You cannot go bald without first losing your hair: telogen effluvium is a precursor to, prerequisite for and potentially an incitant to common baldness in men

Abstract Background Telogen effluvium (TE) is defined by an increased ratio of hairs in telogen to hairs in anagen. Diagnosis is not contingent on a self-reported quantum of telogen shedding. Androgenetic alopecia (AGA) is diagnosed histologically by follicular miniaturization. TE and AGA can both produce balding; however, their relative contributions and the sequence of these events are unknown. Objectives To correlate individual fibre diameter (a proxy for follicular miniaturization) with anagen and telogen duration to determine whether TE precedes or follows AGA. Methods Healthy men aged 18–55 years with stage 3–5 vertex balding had serial tattoo-directed phototrichograms on days 1, 84 and 112. Individual hairs were tracked with computer-assisted hair-to-hair matching. Fibre diameter was measured. Anagen and telogen duration were mathematically calculated using the fraction of anagen and telogen hairs that remained in the same cycle phase between follow-up examinations. Results There was a linear correlation between fibre diameter and anagen duration. Thin fibres (60 µm) had a shortened mean (SD) anagen duration of 200 (72) days. In balding scalps, thick anagen fibres (> 80 µm) also had a shortened mean anagen duration of 580 (150) days. Telogen duration did not vary with fibre diameter. Conclusions In men, a shortening of anagen duration precedes fibre diameter reduction. The clinical correlate of anagen shortening is TE, while reduction in fibre diameter correlates with follicle miniaturization and AGA. While visible TE occurs years in advance of visible balding in women with long hair, TE may go unnoticed in men with short hair. The observed sequence of events establishes that TE is a precursor to AGA. Failure to observe shedding does not negate a diagnosis of TE. We have developed a new model to describe the pathogenesis of balding.