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I now have comprehensive, textbook-sourced information to give a thorough answer. Here it is:
Hair Loss (Alopecia) - Complete Overview
1. Types & Causes
Hair loss broadly falls into non-scarring (reversible) and scarring (permanent follicle destruction) categories. The major types are:
Androgenetic Alopecia (AGA) - Most Common
- Affects up to 80% of men and 50% of women over their lifetime.
- Caused by progressive miniaturization of terminal hair follicles driven by dihydrotestosterone (DHT), a testosterone metabolite converted by 5α-reductase enzymes.
- Genetically determined - polygenic, with the androgen receptor gene (AR) on chromosome Xq11-12 being the major determinant in men.
- In men: frontotemporal recession and vertex thinning (Hamilton-Norwood scale, Types I-VII).
- In women: diffuse crown thinning with preserved frontal hairline (Ludwig pattern). In premenopausal women it can signal hyperandrogenism (check for hirsutism, acne).
Norwood Scale for Male Pattern Hair Loss:
Telogen Effluvium (TE) - Diffuse Shedding
- Acute TE: A large number of follicles enter the resting (telogen) phase simultaneously due to a trigger. Hair shedding begins ~3 months after the triggering event.
- Common triggers include: surgery, childbirth, high fever, severe physical/emotional stress, crash dieting, iron deficiency, thyroid disorders, and many drugs (see list below).
- COVID-19: Severe TE is well-documented 2-3 months after SARS-CoV-2 infection.
- Acute TE: shedding >100-200 hairs/day. Typically self-resolves once the trigger is removed.
- Chronic TE: mostly middle-aged women, mild shedding (<100/day), temporal thinning, often unexplained. No consistently effective treatment.
Alopecia Areata (AA) - Autoimmune Patchy Loss
- Round or oval patches of complete hair loss, typically 1-5 cm in diameter, on scalp, beard, eyebrows, eyelashes.
- Autoimmune - autoreactive CD8+ T cells target follicular melanocytes; the hair bulb's immune privilege collapses.
- Key clues: "exclamation point" hairs (tapered at base), yellow/black dots on dermoscopy, nail pitting in ~10% of cases.
- Variants: Alopecia totalis (complete scalp), Alopecia universalis (all body hair), Ophiasis (band-like temporal/occipital loss).
- Associated with atopic dermatitis, thyroiditis, SLE, vitiligo, Down syndrome.
- ~25% have a positive family history.
Anagen Effluvium
- Acute diffuse loss starting 4-6 weeks after chemotherapy or scalp radiation, up to 1000 hairs/day.
- Usually regrows after therapy ends; permanent alopecia possible with high-dose radiation or busulfan/docetaxel regimens.
- Scalp hypothermia (cooling cap) can prevent or reduce loss during chemo.
Drugs That Cause Hair Loss
From Goldman-Cecil Medicine, notable culprits include:
- Anticoagulants (warfarin, heparin, apixaban, rivaroxaban)
- Antiepileptics (valproic acid, carbamazepine)
- Antithyroid drugs, beta-blockers, ACE inhibitors
- Oral contraceptives, androgens, aromatase inhibitors
- Retinoids, lithium, interferons
2. Diagnosis & Investigations
| Test | What it shows |
|---|---|
| Pull test | Grasp 40 hairs, slow pull - >4-6 club hairs = abnormal (TE); >6 anagen hairs = anagen effluvium |
| Blood tests | CBC, TSH, ferritin/iron, vitamin D, B12, zinc, androgens (DHEAS, testosterone, LH/FSH in women), ANA |
| Dermoscopy (trichoscopy) | Yellow dots, exclamation-point hairs (AA); miniaturized vellus hairs (AGA) |
| Scalp biopsy | Definitive for scarring alopecias; distinguishes AA from other types histologically |
| Light microscopy | Assesses hair shaft disorders |
| Trichogram | 50 hairs plucked - ratio of anagen:telogen:dystrophic hairs |
Key principle: Diffuse hair loss without visible alopecia is common in TE because 50% of hairs must be lost before density reduction is visible.
3. Treatment
Androgenetic Alopecia
| Treatment | Details |
|---|---|
| Topical minoxidil | 2% or 5% solution/foam applied daily; increases anagen duration and follicle size; first-line for both sexes |
| Low-dose oral minoxidil | 0.625-2.5 mg/day (women), 2.5-5 mg/day (men); growing evidence of safety and efficacy |
| Finasteride (oral, 1 mg/day) | FDA-approved for men; inhibits type II 5α-reductase; hair growth peaks at 1-2 years; must continue indefinitely or AGA returns; not for women of childbearing age |
| Dutasteride | Inhibits both type I and II 5α-reductase; more potent than finasteride |
| Spironolactone | Anti-androgen for women; especially useful in women also getting facial hypertrichosis from oral minoxidil |
| PRP (Platelet-Rich Plasma) | Autologous injections of growth factors; evidence mixed - some RCTs show no benefit over saline |
| Low-level laser therapy (LLLT) | FDA-cleared device; modest improvement in hair density in small studies |
| Hair transplantation | Gold standard surgical option; follicular unit transplantation (FUT/FUE) - natural-appearing results; patients should continue minoxidil/finasteride post-op to preserve results |
Minoxidil side effects: Hypertrichosis of cheeks/forehead (more with oral), headache, ankle edema, contact dermatitis (topical), hypotension, tachycardia (oral - rare at low doses).
Finasteride side effects (<2%): Decreased libido, erectile dysfunction. Rare: gynecomastia, depression. Lowers PSA by ~50% (inform patient and physician). "Post-finasteride syndrome" (persistent sexual dysfunction, brain fog) is controversial but FDA has added suicidal ideation warning to the label (2025 update).
Alopecia Areata
| Treatment | Details |
|---|---|
| Intralesional corticosteroids | Triamcinolone acetonide injected intradermally; first-line for limited patchy AA |
| Topical/systemic corticosteroids | Used for more extensive disease |
| JAK inhibitors | Ritlecitinib (FDA-approved 2023) and baricitinib (FDA-approved) are now standard for moderate-to-severe AA; ritlecitinib vs baricitinib indirect comparison shows similar efficacy (PMID: 39445776, 2025 network meta-analysis) |
| Contact immunotherapy (DPCP/SADBE) | Chemical sensitizers applied to scalp; >60% of patients with widespread patchy AA respond |
| Spontaneous remission | Common in limited AA - high self-remission rate within 12 months |
Telogen Effluvium
- Remove the precipitating cause (treat underlying thyroid/iron deficiency, stop offending drug, address nutritional deficit).
- Acute TE resolves spontaneously in months. Chronic TE has no reliably effective treatment.
- May unmask or worsen underlying AGA.
Anagen Effluvium
- Scalp hypothermia (cooling cap) during chemotherapy - can prevent or reduce loss, including permanent loss from docetaxel regimens.
- Topical minoxidil accelerates regrowth but does not prevent loss.
4. Prevention & Hair Care
- Address nutritional gaps: iron, ferritin, zinc, vitamin D, biotin, protein are the most important. A 2024 systematic review (Wang R et al., Mol Nutr Food Res) confirmed micronutrient deficiencies are common in androgenetic alopecia.
- Avoid tight hairstyles (traction alopecia), excessive heat, and harsh chemical treatments.
- Manage stress (major trigger for TE).
- Maintain scalp hygiene - seborrheic dermatitis worsens hair loss.
- If on medications known to cause TE (valproate, heparin, etc.), proactively monitor hair status.
- Postpartum shedding is physiologic and self-resolving by 9 months - no treatment needed, only reassurance.
Sources: Dermatology 2-Volume Set 5e; Goldman-Cecil Medicine 22e; Andrews' Diseases of the Skin; Fitzpatrick's Dermatology; Harrison's Principles of Internal Medicine 22e (2025).
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