What are the causes of telogen effluvium (hair loss during the telogen phase)?

Causes of Telogen Effluvium (Hair Loss During Telogen Phase)

Telogen effluvium results from physiological or emotional stressors that prematurely push hair follicles into the resting (telogen) phase, causing diffuse shedding approximately 2-3 months after the triggering event. 1

Primary Triggering Events

Physiological Stressors

• Childbirth is one of the most common precipitants, causing abrupt hair shedding 2-3 months postpartum 2, 3
• Major surgery or prolonged anesthesia triggers telogen shift through metabolic stress 4, 5
• Severe febrile illness or high fever episodes disrupt the normal hair cycle 4, 3
• Rapid weight loss causes telogen effluvium at a mean weight loss of approximately 15% body weight or 3.54 kg/month, with women and older adults particularly vulnerable even with less severe weight reduction 5

Nutritional Deficiencies

• Iron deficiency (low serum ferritin) is the most common nutritional cause of diffuse hair loss worldwide and a hallmark of chronic diffuse telogen hair loss 1, 6
• Vitamin D deficiency (<20 ng/mL) shows strong association with hair loss, with 70% of alopecia areata patients deficient versus 25% of controls 1
• Zinc deficiency impairs hair follicle function, with serum zinc levels tending to be lower in patients with telogen effluvium 1, 6
• Folate deficiency may contribute to hair loss 1, 6

Medication-Induced Causes

• Systemic retinoids are well-documented triggers of medication-induced telogen effluvium 7
• Antifungal agents can precipitate telogen shedding 7
• Psychotropic medications including certain antidepressants and mood stabilizers 7
• Chemotherapy agents cause anagen effluvium (a distinct but related phenomenon affecting actively growing hairs) 8, 1
• Anticoagulants and beta-blockers have been associated with hair loss 1

Endocrine Disorders

• Thyroid disease (both hypothyroidism and hyperthyroidism) commonly causes diffuse hair loss 1, 6, 3
• Polycystic ovary syndrome (PCOS) with androgen excess can trigger telogen effluvium 1

Emotional and Psychological Stress

• Severe emotional stress can push follicles prematurely into telogen phase through unknown mechanisms 1, 4, 2

Underlying Mechanisms

Five distinct functional types of telogen effluvium have been proposed based on alterations in different phases of the follicular cycle 9:

• Immediate anagen release – abrupt termination of the growth phase
• Delayed anagen release – prolonged anagen followed by synchronized shedding
• Short anagen syndrome – constitutionally shortened growth phase
• Immediate telogen release – premature shedding of telogen hairs
• Delayed telogen release – prolonged retention followed by mass shedding

Diagnostic Considerations

Key Clinical Features

• Diffuse shedding over the entire scalp occurring 2-3 months after a triggering event distinguishes telogen effluvium from patchy alopecia areata 1
• Positive hair pull test (>6 hairs extracted from a cluster of 40-60 hairs) confirms excessive telogen shedding 1
• The scalp typically appears normal without inflammation or scaling, unlike tinea capitis or scarring alopecia 8, 1

Essential Laboratory Testing

When the diagnosis is uncertain or no obvious trigger is identified, targeted testing should include 1, 6, 3:

• Serum ferritin (optimal ≥60 ng/mL needed for hair growth)
• TSH and free T4 to exclude thyroid disease
• Vitamin D level (deficiency defined as <20 ng/mL)
• Serum zinc
• Complete blood count to assess for anemia
• Folate level if nutritional deficiency suspected

Prognosis and Management

• Spontaneous remission occurs in up to 80% of cases with short duration (<1 year) once the precipitating trigger is identified and removed 6
• The condition is self-limited and typically resolves in 3-6 months after trigger removal 3
• Nutritional supplementation (vitamin D, zinc, iron, folate) may be beneficial if deficiencies are documented 6
• Topical minoxidil 2% can be considered for persistent cases, though the primary treatment remains trigger identification and removal 3

Critical Pitfalls to Avoid

• Do not confuse telogen effluvium with alopecia areata: telogen effluvium shows diffuse shedding without patchy loss or exclamation-mark hairs characteristic of alopecia areata 8, 1
• Failure to identify medication triggers is common because hair loss appears 2-3 months after drug initiation, making the temporal relationship less obvious 7, 2
• Overlooking the psychological impact: the sudden excessive shedding can be extremely distressing and may significantly impact quality of life, warranting psychological support 2
• Ordering excessive laboratory tests when a clear trigger (childbirth, surgery, weight loss) is already identified clinically 1