Both males and females have hair follicles present on the face. At puberty hair follicles on the cheeks, chin, and upper lip regions of the male face transition from vellus to terminal hair, as characterized by an increase in hair follicle diameter and pigmentation. This transition is driven by systemic androgen activity as well as by the local conversion of testosterone to dihydrotestosterone (DHT) as catalyzed by 5a-reductase, and results in the prolongation of anagen in the majority of male facial hair follicles in these regions. The sensitivity of hair follicles to androgens is variable within an individual and may be independent of systemic androgen levels. The intracrine effect of androgens is highlighted by the fact that the conversion of testosterone to DHT is catalyzed by 5a-reductase in the skin and hair follicle. At least two isoforms of 5a-reductase are localized in the skin with the acidic, Type II isoform thought to be the primary form in beard hair follicles [19]. The actions of androgens on hair growth are extensively reviewed elsewhere [20].
Clinical hirsutism has been defined by Ferriman and Gallwey based on the density of terminal hair at eleven different body sites that included the upper lip and chin as well as the areas on the torso and extremities. While the presence of terminal facial hair in women may result from a genetic predisposition based on ethnic extraction, an altered hormonal balance such as in polycystic ovary syndrome (PCOS) or from undefined causes as in the case of idiopathic hirsutism [8], it is clear that the subjective assessment of facial hair has created a dynamic range for which methods of removal and management are desired. Thus, it is important to view facial hair beyond the clinical definition of hirsutism to include both terminal and vellus hair to the extent that it represents a concern, and impacts self-perception.