Exogen Hairs in Women with and without Hair Loss

Contrary to the classical view of the hair cycle, in which telogen is the resting phase that precedes the release of the hair shaft, another phase has been introduced, exogen. Exogen is the phase wherein the processes for the release of the hair shaft are initiated and successfully executed. Exogen ends when the shaft is liberated. Accordingly, human hairs would be preferably released not with telogen but with exogen roots. To better understand this somehow revolutionary point and what occurs in telogen effluvium (TE) and in androgenetic alopecia (AGA), we undertook a morphological study. We examined 25 women of comparable age by collecting shedding hairs by the Modified Wash Test under stringent diagnostic criteria. Eight patients were "normal", 5 had AGA, 9 TE, and 3 had a TE+AGA overlap. Hair roots were divided into early telogen, full telogen, and exogen. Exogens accounted, in normal women, for 2.6% of all hairs, for 5.2% in AGA, for 6.6% in TE, and for 2.3% in TE+AGA, without any significant difference. Our exogen prevalence (2.6%) did not vary in patients with AGA and TE. Therefore, the pathogenetic role of exogen in AGA and TE seems negligible.