Telogen Effluvium

01Pathophysiology

The hair growth cycle consists of three phases: anagen (active growth, lasting 2-6 years), catagen (transition, lasting 2-3 weeks), and telogen (resting phase, lasting about 3 months, after which the hair falls out). Under normal conditions, roughly 85-90% of scalp hair is in anagen and only 10-15% is in telogen at any given time.

In telogen effluvium, a physiological or emotional stressor causes a synchronized premature transition of a disproportionately large percentage of anagen follicles into the telogen phase. Because the telogen phase lasts approximately 3 months, the clinical shedding becomes apparent 2-3 months after the inciting event, not at the time of the stressor itself. This temporal gap is the single most tested concept. Exam vignettes deliberately place the stressor in the patient's history to see if you can connect a remote event to the current complaint.

The shedding is diffuse because the shift affects follicles across the entire scalp rather than in a localized pattern. The follicles themselves are structurally normal and not destroyed, which is why this condition is classified as non-scarring alopecia and why full regrowth is expected once the trigger is removed.

The hallmark finding on microscopy or gross inspection of a shed hair is the club-shaped (bulb) root, indicating a telogen hair that has completed its resting phase and detached normally from the follicle. This distinguishes it from anagen effluvium, where the hair breaks off with a tapered or fractured shaft because the follicle was damaged mid-growth.

02Classification and Clinical Manifestation

Clinical Manifestation

03Diagnostic Workup

Telogen effluvium is primarily a clinical diagnosis. The most important diagnostic tool is a careful history linking the onset of shedding to a stressor that occurred 2-3 months earlier. The hair pull test is the best initial bedside assessment: you grasp approximately 40-60 hairs between the thumb and forefinger, apply gentle traction, and count the hairs that come out. If more than 10% release easily and all have a club-shaped root, this is strongly consistent with telogen effluvium.

Laboratory testing is directed at identifying a correctable underlying cause rather than confirming the diagnosis itself. TSH and ferritin are the two highest-yield labs to order. Ferritin is worth special attention because a value below 30-40 ng/mL may drive hair shedding even when hemoglobin is still within normal range, meaning you cannot rely on CBC alone to rule out iron-related hair loss.

Scalp biopsy is reserved for cases where the diagnosis is unclear or chronic shedding does not improve despite trigger removal. Histopathology will show an increased proportion of telogen follicles (normal is approximately 10-15%; in telogen effluvium this rises above 25%) without inflammatory infiltrate, fibrosis, or follicular miniaturization. The absence of miniaturization is what separates this from androgenetic alopecia on biopsy.

04Management and Treatment

The cornerstone of management is identifying and removing the inciting trigger. For acute telogen effluvium, no pharmacologic intervention is strictly necessary because the condition is self-limited. Once the triggering stressor has resolved, the shifted follicles re-enter anagen and new hair growth becomes visible within 3-6 months.

Reassurance is a testable management step. Vignettes may present a distressed postpartum patient with diffuse hair loss and normal labs, and the correct "next best step" is reassurance and observation, not medication.

When labs reveal a correctable deficiency, targeted supplementation is indicated. Iron replacement with ferrous sulfate 325 mg daily is the standard when ferritin is low. The goal is to bring ferritin above 40-70 ng/mL. Concurrent vitamin C (250-500 mg) improves absorption. Avoid taking iron with calcium, antacids, or tea, as these reduce absorption.

For chronic telogen effluvium that has persisted beyond 6 months without a clear remediable cause, topical minoxidil 5% may be offered to promote regrowth. Minoxidil shortens the telogen phase and stimulates follicles back into anagen. It is not a cure but can reduce the duration and severity of shedding. Patients should be counseled that an initial increase in shedding may occur during the first 2-4 weeks of minoxidil use (as miniaturized telogen hairs are pushed out by new anagen hairs), and this is expected, not a reason to discontinue.

There is no role for systemic corticosteroids, intralesional injections, or immunosuppressants in telogen effluvium.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students miss telogen effluvium questions is by failing to connect the temporal gap between the stressor and the onset of shedding. The vignette will almost always bury the trigger 2-3 months back in the history (a delivery, a febrile illness, a surgery, a period of severe caloric restriction). If you are scanning only the present complaint, you will miss the diagnosis entirely and default to a wrong answer like androgenetic alopecia or alopecia areata.

A second frequent trap involves the postpartum patient. The vignette may describe a woman 3-4 months after an uncomplicated delivery who is alarmed by excessive hair shedding. Students may overthink this and consider postpartum thyroiditis or nutritional depletion from breastfeeding. While those should be screened for with TSH and ferritin, the answer in a straightforward vignette with normal labs is telogen effluvium with reassurance as the management.

The third trap is confusing telogen effluvium with anagen effluvium. Both cause diffuse hair loss, but the timing and hair morphology are different. Anagen effluvium begins within days to weeks of the insult (classically chemotherapy), and the hairs are broken and dystrophic. Telogen effluvium appears months later, and the hairs have intact club bulbs. If a vignette mentions chemotherapy and hair loss occurring within 1-2 weeks of treatment, that is anagen effluvium, not telogen.

Finally, remember that telogen effluvium never causes complete baldness and never causes scarring. If the vignette describes scarring, atrophy, or permanent follicular destruction, you are dealing with a scarring alopecia (lichen planopilaris, discoid lupus, central centrifugal cicatricial alopecia), and telogen effluvium should be eliminated immediately.

The core competency being tested is your ability to recognize a pattern of diffuse, non-scarring hair loss with a delayed onset relative to a physiological stressor, and to sequence your workup and management correctly: history and hair pull test first, targeted labs to exclude treatable triggers, and reassurance as the primary intervention.