Background: A novel phenomenon has been described by the phototrichogram: the emptiness of the follicle after teloptosis. We called this phenomenon kenogen, from the Greek ĸΕνóς, ‘empty’. Objective: To describe the kenogen phase in its details. Methods: Analysis of the existing literature. Results: The original observation in 2 women was confirmed in 10 balding and non-balding males studied for 14 years in whom kenogen lasted about 4 months increasing up to about 7 months and affecting 80% of all hair cycles. In 2 women with progressing androgenetic alopecia studied for 2 years, kenogen involved 22% of the hair follicles, lasting from 3 months to 1 year. In a prepubertal boy studied for 1 year, it involved 8% of hairs and lasted about 2 months. Conclusion: During kenogen, the hair follicle rests physiologically, but duration and frequency are greater in androgenetic alopecia, possibly accounting for baldness. In addition to the classical cycle, the hair follicle may follow an alternative route during which the telogen phase, not accompanied by a coincident new early anagen, ends with teloptosis leaving the follicle empty.

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