Telogen effluvium is a stress-triggered hair loss condition. The stress stimulus affects the normal hair growth cycle by which lags in between the hair growth stages occur. Under the normal cycle, it is normal to lose 50–100 hair shafts a day. Due to the stress stimulus, the growth phase shortens while the shedding phase lengthens. This leads to massive hair loss. However, once the stimulus is corrected, hair growth returns to normal.

There are two types of this condition. The trigger is well-recognised when the condition is acute. Hair loss begins several months since the stressor took place. On the other hand, in the cases of chronic hair loss, the trigger is either prolonged or repeated, hair loss continues for more than the usual six months.