Resting No More: Redefining Telogen, the Maintenance Stage of the Hair Growth Cycle

The document from 2014 redefines the telogen phase of the hair growth cycle, traditionally seen as a resting phase, as a period of significant biological activity and clinical importance. It introduces the concept of early 'refractory' and late 'competent' sub-stages within telogen, each with distinct regenerative responses. The study identifies a 'telogen signature' of 425 genes that are dynamically regulated during this phase, preparing the hair follicle for the next growth phase by modulating inhibitory and activating pathways. The document also discusses the role of circadian rhythms and immune function changes during telogen, suggesting that this phase is not passive but involves active hair growth inhibition and preparation for regeneration. Clinically, understanding the nuances of telogen is essential for addressing hair growth disorders, as the response to treatments like minoxidil or finasteride depends on the sub-stage of telogen the hair follicle is in. The paper concludes that telogen is a biologically active, energy-efficient phase that is crucial for hair fiber maintenance and the dynamic renewal of the mammalian hair coat.