telogen

Telogen is the resting phase of the hair growth cycle in humans and many mammals. Hair follicles cycle through anagen (growth), catagen (regression), and telogen (rest). During telogen, hair follicles are dormant and the existing hair remains anchored in the follicle while the surrounding matrix activity declines. The follicle remains quiet until re-entering anagen.

In scalp hair, about 10-15% of follicles are in telogen at any given time. The telogen phase lasts roughly two to four months, commonly around three. At the end of telogen, the follicle re-enters anagen and a new hair begins to grow; the old hair may shed during exogen.

Telogen effluvium is a diffuse shedding condition caused by an abnormal shift of hairs from anagen into telogen. Triggers include acute illness, surgery, childbirth, malnutrition, iron deficiency, thyroid disorders, and certain medications. Onset is typically 2-3 months after the trigger, with regrowth often within 6-12 months after resolution.

Diagnosis is clinical; a hair pull test and, if needed, trichoscopy can aid assessment. Treatment focuses on addressing the underlying cause and ensuring adequate nutrition. Most people recover fully, though chronic telogen effluvium can occur if the trigger persists or is not addressed.