The genetically programmed hair growth cycle and alopecia: what is there to know?

Abstract

Although commonly dismissed as being of superficial importance, the hair follicle is one of human biology's most fascinating structures. One should not diminish the role of hair as a social and sexual communication signal in humans, as evidenced by the significant psychological trauma associated with its absence from the human scalp. Along with skin pigmentation, the hair fiber contributes much to the phenotypic variation between different human populations and can be significantly altered in its appearance. The last 20 years have seen a vast change in research activity into the regulation of hair growth in health and disease and, over the next 5 years, this should include further important glimpses of the nature of the hair follicle's clock machinery (e.g., identification of the stop/start signals and triggers). Therapeutic and cosmetic manipulation of this mini organ will require a careful balance between delivery to the follicle of stimuli that are as specific as possible, while leaving other systems as unaffected as possible. Thus, successful technologies will need to be designed for targeted delivery of topical agents with the minimum of fuss and colateral damage. This review aims to provide a timely update of salient data for the benefit of both clinicians and researchers alike.

A marine protein-based dietary supplement for subclinical hair thinning/loss: Results of a multisite, double-blind, placebo-controlled clinical trial

“…While the effects of the oral supplement on lowering numbers of shed hairs represented a clear positive benefit, one must also consider possible contributions of seasonal shedding, even in humans. [ 38 39 ] This study was mapped carefully to seasonal influence on hair growth dynamics. Both the Dallas and Colorado Springs trials were conducted over the same period of the year (April/May-November).…”

“…In healthy human adult scalp the proportion of hair follicles in the anagen or growth phase peaks in March, and falls steadily to lowest anagen in September when the hair follicles are already in late telogen or have moved to exogen (active shedding phase). [ 38 39 ] Thus, one can expect that the number of shed hairs to peak in August/September, that is, when the fewest hair follicles are in anagen. Baseline data in the current study were gathered in spring (April in Colorado; May in Texas), that is, not be peak time for normal healthy scalp shedding.…”

Hidradenitis suppurativa: A folliculotropic disease of innate immune barrier dysfunction?

“…25 Life-long cycling (the only human adult tissue to do so) involves production of hair fibres during anagen (Figure 1A), followed by an apoptosisdriven regression of approximately two thirds of the HF's cellular mass during catagen, and a period of relative rest during telogen until the next anagen phase re-starts the cycle. 26,27 In intertriginous regions of the skin, the pilosebaceous unit is further expanded to include apo-eccrine or apocrine glands. These glands were thought originally to be important in HS, but are now considered to be secondary in disease pathogenesis.…”