Catagen and Telogen Phases of the Growth Cycle

Abstract

Like numerous other biological processes, the growth of mammalian hair is characterized by cyclic periods of activity which are followed by periods of rest or quiescence. This fascinating process, though familiar to most of us, is still only poorly understood even by dermatologists. All that is known can be summed up rather briefly. We know, for example, that during the life of an animal, a single hair follicle goes through several cycles of growth and rest called respectively anagen and telogen. Two transition periods occur between growth and quiescence and between rest and growth, the first period being known as catagen. When the quiescent follicle resumes its growth, it forms a new hair, which either dislodges the old hair produced during the previous cycle or grows alongside it. Once dislodged, the old hair is shed (Montagna and Parakkal 1974).