Pathologic Dynamics of Human Hair Loss

This study concerns the behavior of the human follicle under stresses which cause temporary loss of hair. Many different agencies cause hair shedding.¹For some years now, I have been watching what happens to the follicle in a variety of natural and experimental alopecic conditions. Out of these observations has grown a biological generalization, the presentation of which is the main business of this essay. To grasp the meaning of this generalization, requires a thorough understanding of the hair cycle, and, in particular, catagen, that brief epoch during which a growing follicle (anagen) becomes transformed into a resting one (telogen). The prelude to the present theme is to be found in a previous paper dealing with the dynamics of human catagen.²Further important readings are Montagna's³analyses of hair cycle mechanics, and a recent study of catagen by Ellis and Moretti.⁴The dynamics of change in