Loading blog post…
A complete guide to telogen effluvium — the hair cycle biology behind the 3-month lag, common triggers (illness, stress, postpartum, crash diets), acute vs. chronic TE, ferritin and thyroid workup, and the evidence-based management approach.
· By MedSpot Editorial · 6 min read
Telogen effluvium (TE) is diffuse hair shedding caused by a disruption of the hair growth cycle — specifically, an abnormal synchronization of hair follicles into the resting (telogen) phase, leading to increased shedding 2–3 months after the triggering event. It is one of the most common causes of hair loss, yet it is frequently misunderstood because the hair falls out months after the event that caused it.
Each hair follicle cycles independently through three phases:
Anagen (growth): Active hair growth phase; lasts 2–7 years (scalp); 85–90% of scalp follicles are in anagen at any given time.
Catagen (regression): Short transitional phase; follicle involutes; 1–2% of follicles; lasts 2–3 weeks.
Telogen (resting): Follicle is dormant; the hair shaft is retained but not growing; 10–15% of scalp follicles; lasts ~3 months. At the end of telogen, the resting hair is released (shed) and a new anagen hair begins.
Normal shedding: 50–150 telogen hairs per day is normal when ~10–15% of follicles are in telogen. When more follicles shift to telogen simultaneously, shedding increases proportionally.
When a significant physiological stressor occurs:
This is why hair loss appears 2–4 months after the trigger event — the follicles were affected immediately, but the shedding doesn't occur until they complete their telogen phase.
The good news: the follicles are not destroyed. They re-enter anagen and regrow the hair once the trigger has resolved.
Febrile illness: High fever (>39°C) is one of the most reliable TE triggers. COVID-19 became the most-discussed cause of post-infectious TE globally in 2020–2022; hair loss 2–4 months post-infection was reported in 20–30% of COVID survivors. Influenza, typhoid, pneumonia, and other febrile illnesses produce the same effect.
Major surgery: General anesthesia + surgical stress → synchronizes follicle exit from anagen. Typically resolves within 6 months.
Childbirth (postpartum TE): The most common TE trigger. During pregnancy, elevated estrogen prolongs anagen (less shedding → thicker hair during pregnancy). Postpartum estrogen drop → mass synchronous anagen-to-telogen transition → dramatic shedding at 3–4 months postpartum. Affects ~50% of postpartum women. Entirely physiological and self-resolving by 6–12 months.
Severe caloric restriction / crash dieting: Protein and caloric deficiency signals nutrient insufficiency → follicles deprioritized → mass telogen shift. Common after rapid weight loss or very-low-calorie diets. Hair grows back after nutritional status is restored.
Psychological stress: Severe or sustained psychological stress (acute trauma, prolonged anxiety, work burnout) is a documented TE trigger. Mechanism involves HPA axis activation and glucocorticoid effects on follicle cycling.
Iron deficiency: The most evidence-linked nutritional cause of TE. Ferritin (stored iron) level is the key marker — not hemoglobin. Patients with normal hemoglobin can have significantly depleted iron stores. A ferritin level below 30–40 ng/mL is associated with TE; optimal ferritin for hair growth is debated but >70 ng/mL is commonly cited by dermatologists as a target for hair growth support.
Zinc deficiency: Less common; can contribute to TE; associated with severe dietary restriction or malabsorption.
Vitamin D deficiency: Correlation with hair loss has been reported; mechanism not fully established; reasonable to screen and supplement if deficient.
Protein deficiency: Keratin (the hair shaft protein) requires adequate dietary protein for synthesis. Very low protein intake → reduced anagen duration.
Many medications can trigger TE:
Acute TE:
Chronic TE:
For TE lasting >3 months or with no clear trigger:
First line:
If above are normal and TE persists:
This is the primary intervention. TE from iron deficiency responds to iron supplementation. TE from hypothyroidism responds to thyroid hormone. TE from crash dieting responds to nutritional rehabilitation. Without addressing the root cause, symptomatic treatments have limited benefit.
Iron supplementation: For ferritin <30 ng/mL: ferrous sulfate 325 mg daily (taken with vitamin C for absorption; away from coffee/tea/calcium); target ferritin >70 ng/mL over 3–6 months. Monitor ferritin every 3 months during supplementation.
Minoxidil is the only topical agent with meaningful evidence for promoting hair regrowth in TE:
Minoxidil does not treat the cause of TE but supports follicular recovery during regrowth.
Looking for a hair loss consultation? Browse hair restoration providers on MedSpot →