It is a passing, potentially invertible hair loss caused by a sudden and one-step transition of multiple hair from the growth stage (anagen) to the resting stage (telogen). The beginning of the disease is sudden and takes place after 1-6 months following the activity of stimulus, which can result from different physical or psychological factors such as: fever, emotional upset, wound shock, pregnancy, childbirth or a surgical procedure. Additionally, telogen effluvium may appear in case of a thyroid dysfunction, iron deficit, following the cure with oestrogen, during incorrectly balanced diets and while using various medicaments such as: β-blockers, anticoagulants, retinoids, carbamazepine, vaccines. In case of a severe form of telogen effluvium, there may appear a sudden, diffuse, sometimes massive hair loss. There is a lack of complete phalacrosis and hair starts growing back of its own accord after circa 4-6 months.

In trichoscopy there are visible empty connective tissue hair sheaths/ cornified plugs in all areas of a head. Additionally, there appear hair growing back and perifollicular discolourations. This hair is no different in thickness, though in case of long-lasting telogen effluvium there may be prevalence of single hair (connective tissue hair sheaths with a single hair).