The hair cycle disruption mechanism
Normally only 10-15% of scalp hair follicles are in telogen (resting phase) at any time; the rest are in anagen (growth phase). In telogen effluvium, a systemic trigger pushes 30-50% of follicles into telogen simultaneously. Because the telogen phase lasts 2-4 months before shedding, the hair loss isn't visible until weeks-to-months after the trigger event. This delayed onset is why patients often can't connect the trigger to the shedding.
The most common triggers
Headington 1993 (Archives of Dermatology) — the canonical TE characterization — identified the most common triggers in clinical practice: postpartum (peaks 4-6 months after delivery; estrogen-withdrawal mechanism), high fever / acute illness, surgery + anesthesia, severe psychological stress, crash dieting / sudden weight loss, iron deficiency (ferritin under 30 ng/mL per Trost 2006), thyroid dysfunction (both hyper- and hypo-), medications (beta-blockers, lithium, retinoids, anticonvulsants).
Recovery timeline
TE is almost universally self-limited. Without intervention, anagen resumes once the trigger is removed/resolved, and full recovery is typical by 12 months. With trigger-specific intervention (iron repletion if ferritin is low, thyroid management if dysfunction, stress reduction protocol), recovery can shorten to 6-9 months. The hair shed during TE is not lost permanently — it just isn't growing while in telogen.
What actually helps (vs marketing claims)
Highest-evidence interventions: (1) Identify + treat the trigger (ferritin test, thyroid panel, stress audit). (2) For postpartum TE, time is the primary treatment — most cases self-resolve by 12 months (Headington 1993). (3) If ferritin is below 50 ng/mL, repletion with alternate-day iron + vitamin C cofactor (Stoffel 2017). (4) Adequate vitamin D status (Almohanna 2019 — low 25(OH)D associates with chronic TE). Marketing claims about biotin specifically helping TE are NOT supported in non-deficient adults (Patel 2017). See our postpartum hair-loss guide for the full evidence-based recovery protocol.
Primary sources: Headington JT 1993 (Arch Dermatol) — PubMed; Trost LB et al. 2006 (J Am Acad Dermatol); Almohanna HM et al. 2019 (Dermatol Ther).