The Follicular Automaton Model: Effect of Stochasticity and Synchronization of Hair Cycles

The study investigated the dynamics of human hair cycles using a follicular automaton model, which simulates the stochastic transitions of hair follicles through the growth (anagen), arrest (catagen), shedding (telogen), and latency phases. The model was based on long-term observations of ten male volunteers, both alopecic and non-alopecic. It was found that the stochastic model could accurately represent the dynamics of single follicles and the behavior of a population of independently cycling follicles. The study also explored a deterministic version of the model and found that as the number of follicles increased, the steady-state levels of follicles in different phases predicted by the deterministic equations approached those yielded by the stochastic simulations. However, only the stochastic model could reproduce the fluctuations observed in small follicle populations. When synchronization was induced, either by reducing the standard deviation or by an external signal, large-amplitude oscillations in the follicle phases occurred, which are not seen in humans but are similar to moulting in other mammals.