[Cycle of hair growth and evaluation of alopecia]

Hair follows a cycle of growth and involution which is asynchronous among follicles. Three phases are distinguished, namely the anagen growth phase and the catagen and telogen phases of regression. Any kind of alopecia results from perturbations of the hair cycle. Among triggering factors, various hormones, cytokines and apoptosis-inducing agents are currently recognized. Some microorganisms inducing inflammation could modulate the severity of selected hair loss disorders.