Most of the patients complaining of hair loss do not fit the diagnosis of androgenetic alopecia (AGA). This paper’s objective is to describe acute and chronic telogen effluvium (TE), with common occurrences in both sexes and at any age, by clinical and histopathological observation. Acute and chronic TE is described. A possible pathogenic mechanism and a diagnostic approach are suggested, especially to distinguish chronic TE from AGA. Possible therapies are proposed. The recognition of a chronic variant of TE and its distinction from pure AGA, which very often it overlaps, are of paramount importance for a correct clinical and experimental approach to the problems of hair loss.