Background: Depilation has greatly promoted our understanding of hair follicle biology, however, only marginally of telogen (the "resting" stage of the hair cycle). Since electron paramagnetic resonance (EPR) spectroscopy provides an instructive technique for analyzing hair biology, it may be useful for telogen research.
Objectives: To identify differences in murine telogen skin after a spontaneous and depilation-induced hair follicle cycling, and to analyze applicability of EPR to investigate telogen.
Methods: Spontaneous or depilation-induced hair cycling in C57BL/6 mice. EPR spectroscopy of unshaven skin and of shaved hair shafts, microscopical examination of plucked or shed hair shafts, standardized histomorphometry.
Results: Melanin EPR signals did not differ qualitatively between the two examined types of skin, nor did depilation change the hair length. However, unmanipulated telogen skin revealed greater thickness, stronger EPR signals, 25% more hair shafts, and lower melanin content of individual hair shafts, as creating a much more intricate mosaic of telogen hair follicles with various numbers of hair shafts (0-3) than the skin after depilation-induced hair growth. In both types of skin empty pilary canals were found. Both groups of animals lost hair shafts which were typical of exogen (the actively controlled process of hair shedding).
Conclusions: EPR spectroscopy can be profitably employed to study telogen. Murine telogen skin reveals a kenogen-like phenomenon (the "lag" phase following telogen and exogen when hair follicles remain empty, i.e. are devoid of hair shafts). Murine skin thickness in telogen and individual hair shaft pigmentation depend on the way of hair growth induction. Telogens after a spontaneous or depilation-induced hair growth are biologically distinct.