Exogen Hairs in Women with and without Hair Loss

Abstract

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.

Histological characteristics of hair follicles at different hair cycle and in vitro modeling of hair follicle-associated cells of yak (Bos grunniens)

“…While classically categorizing follicles into three stages (anagen, catagen, and telogen), effective determinations can still be made by evaluating the active composite inner root sheath tissues and the global follicle cluster morphology. However, recent studies have identified a fourth phase, the exogen phase, which arises during the transition from telogen to anagen (48)(49)(50). This is characterized primarily by proteolysis at the hair base and active hair shaft shedding.…”

Deflúvio Telogénico Crónico

“…Rebora e colaboradores [14][15][16] consideram dois mecanismos principais para o deflúvio: teloptose prematura/coletiva e entrada prematura em telogénese.…”

The Hormonal Background of Hair Loss in Non-Scarring Alopecias

“…The hair growth process consists of three main phases: anagen, catagen, and telogen, constituting growth, transition, and rest, respectively [ 8 ]. Some authors additionally distinguish an exogen phase, during which hair shaft release is initiated and successfully executed [ 9 ]. The hair cycle entails a complex interplay of various endocrine, autocrine, and paracrine signaling pathways [ 10 ].…”