6.1 Hair Disorders: Non-Scarring & Scarring Alopecia, Hair Shaft Defects & Hirsutism
Key Takeaways
- About 85% to 90% of scalp hairs are in anagen, which lasts about 2 to 7 years, while telogen lasts about 3 months and normal shedding is up to about 100 hairs a day.
- Telogen effluvium usually begins 2 to 3 months after a trigger such as fever, childbirth, surgery, crash dieting, or a new drug, and a pull test yields club (telogen) hairs.
- Baricitinib is approved in the EU for severe alopecia areata in adults, and ritlecitinib is approved for severe alopecia areata from 12 years of age.
- Frontal fibrosing alopecia is a lymphocytic scarring alopecia, mainly of postmenopausal women, causing frontotemporal hairline recession, eyebrow loss, and perifollicular erythema.
- In tinea capitis, Trichophyton infection responds best to oral terbinafine, whereas Microsporum canis responds better to griseofulvin and shows green fluorescence under Wood light.
6.1 Hair Disorders: Non-Scarring & Scarring Alopecia, Hair Shaft Defects & Hirsutism
The first question in any hair consultation is: are the follicular openings preserved? Non-scarring alopecia keeps the openings and is potentially reversible. Scarring alopecia destroys them and is permanent, so it needs early diagnosis and treatment.
The Hair Cycle
| Phase | Duration (scalp) | Proportion of Hairs | Notes |
|---|---|---|---|
| Anagen (growth) | About 2–7 years | 85–90% | Length of anagen sets maximum hair length |
| Catagen (regression) | About 2–3 weeks | About 1% | Apoptosis of the lower follicle |
| Telogen (resting) | About 3 months | 10–15% | Ends with shedding of a club hair |
| Exogen / kenogen | Variable | — | Active shedding; empty follicle before new anagen |
A normal scalp has about 100,000 hairs and sheds up to about 100 a day.
Diagnostic tools: the pull test (gently pulling about 60 hairs; more than about 6 extracted suggests active shedding), trichoscopy (dermoscopy of the scalp), trichogram, and biopsy (4 mm punch, with horizontal and vertical sections) for scarring alopecia.
Non-Scarring Alopecia
Androgenetic Alopecia (AGA)
- Mechanism: dihydrotestosterone-driven follicular miniaturisation in genetically predisposed follicles, with shortening of anagen.
- Male pattern: frontotemporal recession and vertex thinning (Hamilton-Norwood scale).
- Female pattern: diffuse thinning over the crown with a preserved frontal hairline and a widened central part (Ludwig or Sinclair scales). Look for hyperandrogenism (acne, hirsutism, irregular periods).
- Trichoscopy: hair diameter variation of more than 20%, yellow dots, and perifollicular pigmentation.
- Treatment: topical minoxidil (5% for men; 2% or 5% for women); oral finasteride 1 mg for men (the EU label lists mood changes, including suicidal ideation, and sexual side effects); low-dose oral minoxidil and dutasteride (off-label); spironolactone or other antiandrogens in women; platelet-rich plasma; and hair transplantation.
Telogen Effluvium
- Diffuse shedding 2–3 months after a trigger: high fever, childbirth, surgery, crash dieting, severe illness, iron deficiency, thyroid disease, or drugs (retinoids, anticoagulants, beta-blockers, antithyroid drugs).
- The pull test is positive with club (telogen) hairs.
- Check ferritin, thyroid function, and other causes suggested by the history. Acute telogen effluvium recovers within about 6 months once the trigger is removed. Chronic telogen effluvium lasts over 6 months, typically in middle-aged women.
Anagen Effluvium
Abrupt loss of growing hairs within days to weeks of chemotherapy (especially taxanes and anthracyclines), radiotherapy, or poisoning (thallium). Scalp cooling reduces chemotherapy-related loss. Regrowth is usual, except for permanent alopecia after some regimens such as high-dose busulfan or docetaxel.
Alopecia Areata (AA)
- Autoimmune: T-cell attack on the anagen hair bulb after loss of immune privilege, driven by interferon-gamma and IL-15 through JAK signalling.
- Clinical: round smooth patches, alopecia totalis (whole scalp), alopecia universalis (whole body), and ophiasis (band along the occipital and temporal margin, with a poor prognosis). Nail pitting and trachyonychia are common.
- Trichoscopy: exclamation-mark hairs, yellow dots, black dots, broken and tapered hairs.
- Associations: atopy, autoimmune thyroid disease, vitiligo, and Down syndrome.
- Severity: the SALT score (Severity of Alopecia Tool) gives the percentage of scalp hair loss. SALT ≥ 50 is severe.
- Treatment: intralesional triamcinolone for limited patches; potent topical corticosteroids; contact immunotherapy (diphenylcyclopropenone); systemic corticosteroid pulses; and the oral JAK inhibitors baricitinib (EU-approved for severe AA in adults) and ritlecitinib (EU-approved for severe AA from 12 years). Relapse is common after stopping.
Tinea Capitis
- Most common in children. Organisms: endothrix Trichophyton tonsurans (common in urban Europe) and T. violaceum; ectothrix Microsporum canis (from cats and dogs, green fluorescence under Wood light).
- Patterns: scaly patches, "black dot" broken hairs, diffuse scale like seborrhoeic dermatitis, pustules, and kerion (a boggy inflammatory mass that can scar).
- Treatment must be oral: Trichophyton responds best to terbinafine; Microsporum responds better to griseofulvin (not available in all European countries) or itraconazole. Use antifungal shampoo to reduce spread, and screen family members.
Trichotillomania
Compulsive hair pulling produces bizarre patches with broken hairs of different lengths. Trichoscopy shows flame hairs, V-sign, coiled hairs, and hair powder. Management is behavioural (habit-reversal training), with N-acetylcysteine as an option. This is covered further in the psychodermatology section.
Primary Scarring (Cicatricial) Alopecia
| Group | Disorders | Features and Treatment |
|---|---|---|
| Lymphocytic | Discoid lupus erythematosus; lichen planopilaris; frontal fibrosing alopecia (FFA); central centrifugal cicatricial alopecia; pseudopelade of Brocq | LPP: perifollicular erythema and scale. FFA: frontotemporal recession, eyebrow loss, facial papules, "lonely hairs", mostly postmenopausal women. Treatment: potent and intralesional steroids, hydroxychloroquine, 5-alpha-reductase inhibitors (FFA), doxycycline |
| Neutrophilic | Folliculitis decalvans; dissecting cellulitis | Folliculitis decalvans: pustules and tufted hairs, linked to Staphylococcus aureus; treat with clindamycin + rifampicin or doxycycline. Dissecting cellulitis: boggy nodules and tunnels, part of the follicular occlusion tetrad; isotretinoin, TNF inhibitors |
| Mixed | Acne keloidalis nuchae; folliculitis (acne) necrotica | Acne keloidalis: papules and keloidal plaques on the occiput of men with curly hair |
Hair Shaft Abnormalities
| Defect | Appearance | Association |
|---|---|---|
| Monilethrix | Beaded hair with fragile constrictions | Keratin gene mutations (KRT81, KRT83, KRT86) |
| Pili torti | Hair twisted 180° on its axis | Menkes disease (ATP7A, copper transport) and other syndromes |
| Trichorrhexis invaginata ("bamboo hair") | Distal shaft telescoped into proximal shaft | Netherton syndrome (SPINK5) |
| Trichorrhexis nodosa | Frayed nodes like two brushes pushed together | Weathering, arginosuccinic aciduria |
| Trichothiodystrophy | "Tiger-tail" banding under polarised light | Low sulphur content; some forms have photosensitivity |
| Uncombable hair syndrome | Spun-glass hair that cannot be combed flat; triangular shaft | Usually improves in childhood |
Hirsutism and Hypertrichosis
- Hirsutism: male-pattern terminal hair growth in women, scored by the modified Ferriman-Gallwey scale (cut-offs vary by ethnicity, often about 8). The most common cause is polycystic ovary syndrome. Rapid onset with virilisation suggests an androgen-secreting tumour. Treatment: combined oral contraceptives, antiandrogens, topical eflornithine, and laser hair removal.
- Hypertrichosis: excess hair in a non-androgen pattern, either congenital or acquired (drugs such as ciclosporin, minoxidil, and phenytoin; porphyria cutanea tarda; anorexia nervosa). Acquired hypertrichosis lanuginosa can signal internal malignancy.
A 35-year-old woman notices diffuse hair shedding 3 months after an emergency caesarean section and a severe post-partum infection. The pull test yields many club hairs. What is the most likely diagnosis?
A 34-year-old man has alopecia areata with 80% scalp hair loss (SALT score 80) for 2 years despite topical and intralesional corticosteroids. Which oral treatment is approved in the EU for this situation?
A 7-year-old boy has a scaly patch of hair loss with broken hairs. Wood light shows bright green fluorescence, and he has a pet kitten. Which treatment is most appropriate?
A 62-year-old woman has gradual recession of the frontal and temporal hairline, loss of the eyebrows, perifollicular erythema at the hair margin, and small skin-coloured papules on the face. What is the most likely diagnosis?