Common Causes of Hair Loss
Hair loss has multiple distinct etiologies that can be systematically categorized into nonscarring and scarring types, with the most common causes being androgenetic alopecia, alopecia areata, telogen effluvium, tinea capitis, and traction-related hair loss. 1, 2
Nonscarring Alopecias (Most Common)
Patterned Hair Loss
- Androgenetic alopecia (AGA): The single most common cause of hair loss, affecting over 80 million people in the United States. This is typically genetic with characteristic patterns—male pattern shows frontal and vertex thinning, while female pattern shows diffuse crown thinning with frontal hairline preservation 2, 3
Focal Hair Loss
Alopecia areata: A chronic inflammatory autoimmune condition presenting as smooth, round patches of complete hair loss with characteristic "exclamation mark hairs" (short broken hairs at expanding margins). About 20% have family history, and 34-50% recover within 1 year, though recurrence is nearly universal. Disease severity at presentation predicts outcome—68% with <25% hair loss recover vs only 8% with >50% hair loss 1
Tinea capitis: Fungal scalp infection predominantly affecting prepubertal children. In the UK, Trichophyton tonsurans accounts for 50-90% of cases. Presents with patchy alopecia, scaling, and erythema. Clinical patterns include:
- Grey patch (ectothrix Microsporum): fine scaling with dull grey patches
- Black dot (endothrix Trichophyton): broken hair stubs creating "black dot" appearance
- Inflammatory variants with pustules and kerions 4, 3
Trichotillomania: Hair-pulling disorder where broken hairs remain firmly anchored in anagen phase (unlike exclamation mark hairs in alopecia areata). Hair loss is incomplete and irregular 1, 5
Traction alopecia: Caused by chronic tension on hair follicles from tight hairstyles 2, 3
Diffuse Hair Loss
Telogen effluvium: Most common cause of diffuse shedding. Results from physiologic/emotional stress, nutritional deficiencies, or endocrine imbalances that shift hair follicles prematurely into telogen (resting) phase. Self-limited once trigger is removed, with regrowth expected 2, 6, 3
Anagen effluvium: Abnormal hair loss during growth phase, most commonly from chemotherapy or radiation therapy that impairs follicular mitotic activity 1, 2, 3
Scarring Alopecias (Less Common, Require Specialist Evaluation)
These cause permanent follicular destruction and include:
- Frontal fibrosing alopecia
- Discoid lupus erythematosus
- Lichen planopilaris
- Folliculitis decalvans 7
Differential Diagnosis Considerations
The British Association of Dermatologists guidelines specifically identify conditions that cause diagnostic confusion with alopecia areata 1, 5:
- Trichotillomania (most confusing)
- Tinea capitis (scalp inflammation may be subtle)
- Early scarring alopecia
- Telogen effluvium
- Anagen effluvium (drug-induced)
- Systemic lupus erythematosus
- Secondary syphilis
Critical Diagnostic Pitfalls
Do not routinely screen for iron deficiency in alopecia areata patients—while one small case series suggested increased prevalence in women, two subsequent studies failed to confirm this, and no studies demonstrate treatment response to iron replacement 1
Do not underestimate psychological impact—patients with moderate to severe hair loss commonly experience anxiety, depression, reduced work productivity, and significantly impaired quality of life. This affects morbidity even when the condition itself doesn't impact general health 1, 2
Dermoscopy is fundamental for diagnosis of all hair disorders and can distinguish between conditions (e.g., yellow dots in alopecia areata vs different patterns in trichotillomania or scarring conditions) 1, 7