What is the etiology of my hair loss?

What is the Etiology of Hair Loss?

Hair loss has multiple distinct etiologies that must be systematically differentiated through clinical pattern recognition, with the most common causes being androgenetic alopecia (pattern hair loss), alopecia areata (autoimmune), telogen effluvium (stress/physiologic), and infectious/scarring alopecias.

Primary Categories of Hair Loss Etiology

Non-Scarring Alopecias (Most Common)

Androgenetic Alopecia (Pattern Hair Loss)

• Most common form of hair loss affecting over 80 million people in the United States 1
• Etiology: Genetic predisposition + androgen sensitivity in hair follicles 2
• The genetic factor resides primarily in end-organ response—follicular receptivity to androgens delivered to the hair papilla/matrix unit 3
• Results in progressive miniaturization of hair follicles with terminal-to-vellus hair ratio <3:1 (normal is 7:1) 2
• In women, presents as central scalp thinning (Ludwig pattern); in men, frontotemporal and vertex loss
• Critical pitfall: Often misdiagnosed as other conditions when it presents diffusely in women 4

Alopecia Areata

• Etiology: Autoimmune disease with T-lymphocyte-mediated attack on hair follicles 5
• Genetic predisposition (20% have family history) with associations to MHC genes, cytokine genes, and immune regulatory genes 5
• Pathophysiology involves failure of hair follicle immune privilege 5
• Presents as patchy hair loss with exclamation mark hairs at margins
• Hair follicles remain preserved—potential for regrowth exists even in longstanding disease 5

Telogen Effluvium

• Etiology: Physiologic or emotional stress causing synchronized shift of hair follicles into telogen (resting) phase 6
• Triggers include: pregnancy, major surgery, severe illness, medications, nutritional deficiencies, psychological stress
• Presents as diffuse hair shedding 2-3 months after triggering event
• Self-limited once precipitating cause removed 6
• Key distinction from androgenetic alopecia: Terminal-to-vellus ratio remains normal (9:1), no miniaturization 2

Chronic Telogen Effluvium (CTE)

• Most common condition requiring differentiation from female pattern hair loss 2
• Diffuse scalp thinning in middle-aged women with persistent shedding
• No frontoparietal or central pattern; often bitemporal recession
• Hair pull positive from multiple scalp areas including occiput 2
• Etiology: Believed due to synchronization phenomena of cyclic hair growth 4

Scarring (Cicatricial) Alopecias

Central Centrifugal Cicatricial Alopecia (CCCA)

• Etiology: Lymphocytic infiltration causing permanent follicle destruction 2
• Primarily affects African American women
• May represent underlying androgenetic alopecia becoming inflammatory with hair care practices (hot combs, relaxers, occlusive ointments) 2
• Presents with central/frontal/vertex loss progressing to frank baldness with absent follicular ostia

Frontal Fibrosing Alopecia (FFA)

• Etiology: Lymphocytic infiltrate characteristic of lichen planopilaris 2
• Primarily postmenopausal white women
• Receding hairline with perifollicular erythema and eyebrow loss
• One of most frequent causes of cicatricial alopecia despite only being described in 1994 2

Fibrosing Alopecia in Pattern Distribution (FAPD)

• Central hair loss in Ludwig pattern with perifollicular erythema
• Biopsy shows lichen planopilaris 2

Infectious Causes

Tinea Capitis

• Etiology: Fungal infection of scalp
• Scalp inflammation (may be subtle) with patches of hair loss 5
• Requires systemic antifungal treatment 6

Traumatic/Behavioral Causes

Traction Alopecia

• Etiology: Chronic tension on hair from styling practices
• Treatment requires decreasing tension on hair 1

Trichotillomania

• Etiology: Impulse-control disorder causing self-induced hair pulling 5
• Incomplete hair loss with broken hairs firmly anchored (remain in anagen phase) 5
• Treatment targets underlying psychiatric condition 6

Drug-Induced Hair Loss

Anagen Effluvium

• Etiology: Impaired mitotic activity of hair follicles, most commonly from chemotherapy 5, 6
• Abnormal diffuse loss during growth phase
• Can mimic diffuse alopecia areata 5

Systemic Disease-Related Hair Loss

Hair loss can signal underlying systemic conditions including 7:

• Autoimmune diseases (lupus erythematosus, thyroid disease)
• Endocrine disorders (thyroid dysfunction, hormonal imbalances)
• Nutritional deficiencies (though iron deficiency testing not routinely recommended in alopecia areata) 5
• Infectious agents
• Malnutrition

Diagnostic Approach to Determine Etiology

Pattern Recognition is Key:

1. Diffuse loss → Consider telogen effluvium, chronic telogen effluvium, diffuse androgenetic alopecia, anagen effluvium
2. Patterned loss → Androgenetic alopecia (frontoparietal/central in women; frontotemporal/vertex in men)
3. Patchy loss → Alopecia areata, tinea capitis, traction alopecia, trichotillomania
4. Scarring features → CCCA, FFA, FAPD (requires dermatology evaluation)

Physical Examination Findings:

• Exclamation mark hairs at margins → Alopecia areata 5
• Positive hair pull from multiple sites including occiput → Chronic telogen effluvium 2
• Perifollicular erythema → FFA or FAPD 2
• Miniaturization on dermoscopy (varied hair shaft diameters, yellow dots, single hair units) → Androgenetic alopecia 2

When to Biopsy:

• 4-mm punch biopsy with horizontal sections establishes terminal-to-vellus ratio 2
• Terminal-to-vellus ratio <3:1 = androgenetic alopecia
• Terminal-to-vellus ratio 9:1 = chronic telogen effluvium (no miniaturization)
• Lymphocytic infiltrate = scarring alopecia (CCCA, FFA, FAPD)

Laboratory Testing:

• Only when history/examination suggests systemic disease 7
• Consider: thyroid function, autoimmune markers, androgen levels (in women with hyperandrogenism signs)
• Routine iron testing not recommended for alopecia areata 5
• Fungal culture if tinea capitis suspected 5

Critical Clinical Pitfalls

• Don't assume all diffuse hair loss in women is telogen effluvium—androgenetic alopecia commonly presents diffusely in women 4
• Don't miss scarring alopecias—these require urgent dermatology referral as follicle destruction is permanent 2
• Don't overlook psychological impact—patients with moderate to severe hair loss have higher rates of anxiety, depression, and reduced quality of life 1
• Don't forget ethnic variations—normal hair density varies significantly (whites: 36-40 hairs per 4mm biopsy; African Americans: 22; Asians: 16) 2