What causes hair loss in women?

Hair Loss in Women: Causes

Hair loss in women has multiple causes, with androgenetic alopecia (pattern hair loss) being the most common, followed by nutritional deficiencies (particularly iron deficiency affecting 70% of cases), autoimmune conditions like alopecia areata, telogen effluvium from stress, and hormonal imbalances. 1, 2, 3

Primary Causes by Category

Androgenetic Alopecia (Pattern Hair Loss)

• Androgenetic alopecia is the most prevalent form of hair loss in women, affecting over 50% of postmenopausal women and up to 40% of healthy women, often beginning around reproductive age 2, 4
• This condition results from sensitivity to dihydrotestosterone (DHT) and presents with diffuse loss from the parietal or frontovertical areas while maintaining an intact frontal hairline 1, 4
• Can occur with or without elevated androgen levels, and may be associated with polycystic ovary syndrome (PCOS) in women with signs of androgen excess 1, 4

Nutritional Deficiencies

• Iron deficiency accounts for 70.3% of female alopecia cases, making it the single most common nutritional cause 3
• Serum ferritin levels below 60 ng/mL are associated with hair loss, which is substantially higher than the threshold for anemia (5.1 ng/mL), meaning women can have adequate iron for blood production but insufficient iron for hair growth 3
• Vitamin D deficiency shows strong association with hair loss, with 70% of alopecia areata patients having levels below 20 ng/mL versus 25% of controls, and lower levels correlate inversely with disease severity 1
• Zinc deficiency impairs hair follicle function, with serum zinc levels tending to be lower in patients with alopecia areata 1
• Folate deficiency may contribute to hair loss 1

Autoimmune Conditions

• Alopecia areata is an autoimmune condition where T lymphocytes attack hair follicles, causing patchy, non-scarring hair loss that can affect any hair-bearing area 1, 5
• Approximately 20% of affected individuals have a family history, indicating genetic susceptibility 1, 6
• Associated with other autoimmune diseases including thyroid disease (hypothyroidism or hyperthyroidism), lupus, and vitiligo 1, 6
• Characterized by exclamation mark hairs (short broken hairs) around expanding patches, yellow dots on dermoscopy, and cadaverized hairs 1, 5

Stress-Related Hair Loss

• Telogen effluvium occurs when physiologic or emotional stressors push hair follicles prematurely into the resting phase, causing diffuse shedding 1, 7
• Triggered by illness, surgery, childbirth, severe emotional stress, rapid weight loss, nutritional deficiencies, and psychological stress 1, 3
• Psychological stress accounted for 12.3% of cases in one tertiary center study 3

Hormonal Imbalances

• Polycystic ovary syndrome (PCOS) causes hair loss in women with signs of androgen excess such as acne, hirsutism, and irregular periods 1
• Thyroid disease (both hypothyroidism and hyperthyroidism) can cause hair loss, with thyroid disorders accounting for 7.7% of cases 1, 3
• Hyperprolactinemia may contribute to hair loss 1
• Postmenopausal hormonal changes can trigger or worsen hair loss 4

Medication-Induced Hair Loss

• Anagen effluvium occurs when medications, particularly chemotherapy, interrupt actively growing hair follicles, causing rapid and severe hair loss 1, 6
• Various systemic medications can cause hair loss mimicking diffuse alopecia areata 6

Infectious Causes

• Tinea capitis (scalp ringworm) causes patchy hair loss with scalp inflammation and scaling, requiring fungal culture for diagnosis and oral antifungal therapy 1, 5
• Secondary syphilis presents with patchy "moth-eaten" hair loss 1, 5

Physical/Mechanical Causes

• Trichotillomania is compulsive hair pulling that mimics alopecia areata but is distinguished by incomplete hair loss and firmly anchored broken hairs that remain in anagen phase 1, 5
• Traction alopecia results from chronic tension on hair from tight hairstyles 7

Systemic Disease-Related

• Systemic lupus erythematosus can cause both scarring and non-scarring alopecia 1, 5
• Scarring alopecias include lichen planopilaris and central centrifugal cicatricial alopecia 2

Recent Emerging Causes

• COVID-19 vaccination accounted for 6.5% of hair loss cases in one recent study 3

Critical Diagnostic Considerations

When to Suspect Specific Causes

• Look for signs of androgen excess (acne, hirsutism, irregular periods) to identify PCOS or other hormonal causes requiring testosterone, SHBG, and prolactin testing 1
• Check ferritin levels in all women with hair loss, as iron deficiency is present in 70% of cases even when hemoglobin is normal 3
• Examine for exclamation mark hairs and use dermoscopy to identify alopecia areata, looking for yellow dots and cadaverized hairs 1, 5
• Assess pattern of hair loss: diffuse suggests telogen effluvium or nutritional deficiency; patterned suggests androgenetic alopecia; patchy suggests alopecia areata or tinea capitis 6, 7

Laboratory Testing Priorities

• Serum ferritin (target ≥60 ng/mL for adequate hair growth, not just ≥12 ng/mL for anemia prevention) 3
• Vitamin D levels (deficiency defined as <20 ng/mL) 1
• Thyroid stimulating hormone (TSH) and thyroid peroxidase (TPO) antibodies if TSH abnormal 1
• Zinc levels in suspected deficiency 1
• Total or free testosterone, SHBG in women with signs of androgen excess 1
• Fungal culture when tinea capitis suspected 1, 5
• Skin biopsy for difficult cases, early scarring alopecia, or diffuse alopecia areata 1

Common Pitfalls to Avoid

• Do not rely on hemoglobin alone to rule out iron deficiency as a cause of hair loss, as the ferritin threshold for hair growth (60 ng/mL) corresponds to hemoglobin of 13.0-13.8 g/dL, well above the anemia threshold 3
• Avoid ordering excessive laboratory tests when diagnosis is clinically evident, particularly in typical alopecia areata 1
• Do not overlook the psychological impact, which can include anxiety, depression, and reduced quality of life requiring assessment and support 1, 7
• Initiate iron supplementation within 6 months of diagnosis for better prognosis in iron deficiency-related alopecia 3
• Avoid excessive biotin supplementation due to potential diagnostic test interferences 2