What is the main difference between FPHL and telogen effluvium regarding the onset of hair loss?

The primary distinction between Female Pattern Hair Loss (FPHL) and telogen effluvium focuses on the nature and timing of hair loss onset. FPHL manifests as a gradual thinning of hair, particularly on the crown and top areas of the scalp, with a slow progression that can start as early as the late teens or early twenties but typically becomes more apparent with age. In contrast, telogen effluvium presents as a sudden loss of hair, often occurring following a significant stressor, illness, or other factors that trigger a large number of hair follicles to enter the telogen (resting) phase simultaneously.

This sudden onset can result in noticeable thinning within just a few months after the triggering event, while FPHL is characterized by a more chronic and gradual decrease in hair density over time. The underlying mechanisms and risk factors for these two conditions further differentiate them: whereas FPHL is primarily associated with genetic predisposition and hormonal changes, telogen effluvium is largely responsive to stressors, making the timeline and triggers quite different for each condition.