Acne Vulgaris

Acne Vulgaris – High-Yield Study Guide for Medical Students

Definition

Acne vulgaris is a chronic inflammatory disease of the pilosebaceous unit characterized by comedones, papules, pustules, nodules, and possible scarring, most commonly affecting the face, chest, and back.

Epidemiology

Acne vulgaris is one of the most common skin conditions worldwide and a core topic in dermatology for medical students.

• Prevalence: Affects up to 85–90% of adolescents; many continue to have acne into adulthood.
• Age: Peak onset during puberty (ages 12–18). Adult acne, especially in women, is increasingly recognized.
• Sex: Slight male predominance in adolescence (more severe), female predominance in persistent adult acne.
• Distribution: Most commonly involves seborrheic areas with high density of sebaceous glands (face, upper chest, upper back, shoulders).
• Impact: Significant psychosocial burden, including low self-esteem, anxiety, depression, and social withdrawal, often disproportionate to clinical severity.

Pathophysiology

Acne is multifactorial and centers on the pilosebaceous unit. Four key interacting pathogenic mechanisms are tested frequently on exams:

• 1. Increased sebum production:
  • Driven by androgens (testosterone and DHT) acting on sebaceous glands.
  • Enlarged sebaceous glands produce excess sebum, creating a lipid-rich environment.
• 2. Follicular hyperkeratinization:
  • Abnormal desquamation and cohesion of keratinocytes in the follicular infundibulum.
  • Leads to formation of a keratin plug, resulting in comedone formation.
• 3. Cutibacterium acnes (formerly Propionibacterium acnes) proliferation:
  • Anaerobic, Gram-positive rod that colonizes the pilosebaceous unit.
  • Hydrolyzes sebum triglycerides into free fatty acids; activates innate immunity via TLRs, producing pro-inflammatory cytokines.
• 4. Inflammation:
  • Neutrophils, lymphocytes, and macrophages infiltrate around follicles.
  • Rupture of the comedone wall releases keratin, bacteria, and sebum into the dermis, producing papules, pustules, nodules, and possible scarring.

Additional modulators include genetics, hormonal factors (PCOS, congenital adrenal hyperplasia, medications), diet (high glycemic load, dairy in some patients), mechanical occlusion, and cosmetics (acne cosmetica).

Clinical Presentation

Acne vulgaris has a characteristic combination of non-inflammatory and inflammatory lesions in seborrheic areas.

Lesion Types

• Non-inflammatory lesions (comedones):
  • Open comedones (blackheads): Dilated follicular orifice with keratin plug; dark color from oxidized melanin and lipids, not dirt.
  • Closed comedones (whiteheads): Small, flesh-colored papules with a closed follicular opening; more prone to progression into inflammatory lesions.
• Inflammatory lesions:
  • Papules: Small, erythematous, raised lesions.
  • Pustules: Papules with a visible central collection of pus.
  • Nodules: Larger (>5 mm), firm, deep, tender lesions.
  • Cysts: Fluctuant, deep-seated lesions; often nodulocystic acne.
• Sequelae:
  • Scarring: Atrophic (ice-pick, rolling, boxcar) and hypertrophic or keloidal scars.
  • Post-inflammatory hyperpigmentation (PIH): Especially prominent in darker skin phototypes.
  • Post-inflammatory erythema: Residual red macules after active lesions resolve.

Distribution

• Face: Forehead, nose, cheeks, chin.
• Trunk: Upper chest, upper back, shoulders.
• May extend to posterior neck and upper arms in severe cases.

Severity Grading (Clinical/Exam-Oriented)

• Mild acne: Mainly comedones with few inflammatory papules/pustules; minimal trunk involvement.
• Moderate acne: More numerous papules and pustules with comedones; may involve trunk; limited nodules possible.
• Severe acne: Numerous or extensive inflammatory lesions, nodules, cysts; often trunk involvement; high risk of scarring.

Diagnosis

Diagnosis of acne vulgaris is clinical and typically straightforward for medical students and clinicians.

Clinical Diagnosis

• Key features:
  • Presence of comedones (pathognomonic) plus inflammatory lesions (papules, pustules, nodules) in typical distribution.
  • Chronic, relapsing course starting in adolescence.
• History:
  • Onset, duration, lesion evolution, previous treatments.
  • Menstrual history, signs of hyperandrogenism (hirsutism, irregular menses, androgenetic alopecia) in females.
  • Family history of severe acne or scarring.
  • Medication review (corticosteroids, lithium, isoniazid, phenytoin, EGFR inhibitors, androgens).
  • Cosmetic products, occupational exposures, mechanical factors (helmets, sports gear).
• Physical exam:
  • Inspect face, chest, back, shoulders; characterize lesion types and scar burden.
  • Assess for systemic signs of hyperandrogenism or endocrinopathy if indicated.

Investigations

Routine laboratory testing is not required for typical acne vulgaris.

• Consider targeted labs only when:
  • Acne is severe, abrupt in onset, or refractory to standard therapy.
  • Clinical features suggest hyperandrogenism (PCOS, congenital adrenal hyperplasia, androgen-secreting tumor): may check total/free testosterone, DHEAS, LH/FSH, prolactin, 17-hydroxyprogesterone as appropriate.
• Culture or biopsy: Rarely needed; consider biopsy if atypical lesions suggest other diagnoses (e.g., rosacea, folliculitis, gram-negative folliculitis, SAPHO, acne fulminans).

Differential Diagnosis

Important exam and clinical differentials when evaluating acneiform eruptions:

• Rosacea: No comedones; central facial erythema, telangiectasias, triggers (heat, alcohol), possible ocular involvement.
• Periorificial dermatitis: Small papules/pustules around mouth, nose, eyes; typically spares vermilion border; related to topical steroids or cosmetics.
• Folliculitis: Pustules centered on hair follicles; often pruritic; bacterial, fungal, or irritant etiologies.
• Gram-negative folliculitis: May appear after long-term antibiotic therapy for acne; pustular eruption around nose and cheeks.
• Drug-induced acneiform eruptions: Abrupt onset, monomorphic inflammatory papules/pustules, often trunk-dominant; associated with corticosteroids, lithium, isoniazid, phenytoin, EGFR inhibitors, B12, androgens.
• Hidradenitis suppurativa: Deep nodules, abscesses, and sinus tracts in intertriginous areas (axillae, groin, inframammary); scarring more severe and in flexural sites rather than seborrheic areas.

Management

Management is stepwise and tailored to severity, lesion type (comedonal vs inflammatory vs nodular), distribution, and risk of scarring or psychosocial impact. Combination therapy targeting multiple pathogenic pathways is standard of care.

General Principles and Patient Education

• Set expectations: Improvement usually requires 6–8 weeks; explain that initial flare is possible with retinoids.
• Non-comedogenic skincare: Recommend gentle, non-soap cleansers and oil-free, non-comedogenic moisturizers and sunscreen.
• Avoid picking/squeezing: Reduces risk of scarring and PIH.
• Adherence: Emphasize consistent use; address irritation by adjusting frequency rather than abrupt cessation.

Topical Therapy (Mainstay for Mild to Moderate Disease)

1. Topical retinoids (comedolytic and anti-inflammatory; cornerstone of therapy)

• Examples: Adapalene, tretinoin, tazarotene, trifarotene.
• Mechanism: Normalize follicular keratinization, promote comedone clearance, prevent new comedones, anti-inflammatory effects.
• Use: Apply once nightly to entire affected area (not just active lesions). Start every other night if irritation occurs, then increase as tolerated.
• Adverse effects: Irritation, dryness, erythema, photosensitivity. Advise regular moisturizer and sunscreen.

2. Benzoyl peroxide (BP)

• Mechanism: Bactericidal against C. acnes and mildly comedolytic; reduces antibiotic resistance when combined with topical or oral antibiotics.
• Use: 2.5–10% formulations in washes, gels, creams; can be used once or twice daily.
• Caution: Can bleach fabrics; may cause irritation and dryness.

3. Topical antibiotics

• Examples: Clindamycin 1%, erythromycin 2%, minocycline foam.
• Mechanism: Reduce C. acnes and have anti-inflammatory properties.
• Important: Never use topical antibiotics as monotherapy due to resistance risk; always combine with benzoyl peroxide and preferably a retinoid.

4. Other topical agents

• Azelaic acid: Mild comedolytic, anti-inflammatory, and anti-hyperpigmentation; useful in PIH and pregnancy.
• Salicylic acid: Keratolytic; often over-the-counter; mild efficacy in comedonal acne.
• Topical dapsone: Anti-inflammatory; can be useful in adult female inflammatory acne.

Systemic Therapy

Indicated for moderate to severe inflammatory acne, widespread truncal acne, nodulocystic acne, scarring risk, or failure of topical therapy.

1. Oral antibiotics

• First-line classes: Tetracyclines (doxycycline, minocycline; sarecycline in some regions).
• Mechanism: Anti-inflammatory (inhibit neutrophil chemotaxis, MMPs) and antibacterial against C. acnes.
• Use: Combine with topical retinoid and benzoyl peroxide; limit duration (usually 3–4 months) to reduce resistance.
• Alternatives: Macrolides (azithromycin, erythromycin) if tetracyclines contraindicated, though resistance is more common.

2. Hormonal therapy (females)

• Combined oral contraceptives (COCs):
  • Estrogen plus progestin formulations; reduce ovarian androgen production and increase SHBG, lowering free testosterone.
  • Useful in acne with perimenstrual flares, late-onset acne, or clinical hyperandrogenism.
• Spironolactone:
  • Androgen receptor antagonist with mild diuretic effect.
  • Effective in adult female acne; often combined with COCs.

3. Oral isotretinoin

• Indications:
  • Severe nodulocystic acne.
  • Moderate acne with significant scarring or psychosocial distress.
  • Refractory acne not responsive to adequate courses of systemic antibiotics and combination topical therapy.
• Mechanism: Decreases sebum production by sebaceous gland atrophy, normalizes follicular keratinization, reduces C. acnes, and has anti-inflammatory effects.
• Course: Weight-based cumulative dosing over several months; often induces prolonged remission.
• Key considerations:
  • Teratogenicity requires strict pregnancy prevention programs and monitoring.
  • Monitor laboratory parameters according to local guidelines (e.g., lipids, liver function) and screen for mood changes.

Adjunctive and Procedural Therapies

• Intralesional corticosteroids: For large, painful nodules or cysts to rapidly reduce inflammation and prevent scarring.
• Comedone extraction: For resistant comedonal lesions; requires appropriate technique to reduce scarring risk.
• Light and laser therapies: Blue/red light, photodynamic therapy; may be considered as adjuncts in some settings.
• Chemical peels: Superficial peels (e.g., glycolic, salicylic acid) can help comedonal acne and PIH.

Complications and Special Forms

• Scarring: Atrophic and hypertrophic/keloid scars; early, aggressive treatment of severe inflammatory acne can reduce risk.
• Post-inflammatory hyperpigmentation: Especially in darker phototypes; sun protection and agents like azelaic acid or retinoids are useful.
• Acne fulminans: Acute, severe, ulcerative acne with systemic symptoms (fever, arthralgias); requires urgent systemic therapy (e.g., systemic steroids plus isotretinoin).
• Acne conglobata: Severe nodulocystic acne with interconnecting sinus tracts and scarring; often requires isotretinoin.

Key Clinical Pearls for Medical Exams and Practice

• Comedones are essential: Presence of open or closed comedones is the hallmark of acne vulgaris and helps distinguish it from rosacea and folliculitis.
• Topical retinoids are first-line: Use in almost all acne patients unless contraindicated; think of them as the "backbone" of topical therapy.
• Avoid antibiotic monotherapy: Always combine topical or oral antibiotics with benzoyl peroxide to minimize resistance.
• Treat to prevent scars: Scarring is permanent; escalate appropriately (including isotretinoin) in high-risk or refractory cases rather than persisting with suboptimal regimens.
• Consider endocrine causes: In females with late-onset, sudden, or severe acne plus hirsutism or menstrual irregularities, evaluate for PCOS or other hyperandrogenic states.
• Isotretinoin is transformative but high-responsibility: It is the most effective acne drug but requires stringent pregnancy prevention, monitoring, and patient education.
• Acne is not caused by poor hygiene: Overwashing and harsh scrubbing can worsen irritation and inflammation.
• Psychosocial impact matters: Even "mild" acne can cause significant psychological distress; consider this when deciding on treatment intensity and follow-up.

Summary for Medical Students

Acne vulgaris is a high-yield condition driven by increased sebum, follicular hyperkeratinization, C. acnes proliferation, and inflammation. Diagnosis is clinical, based on comedones plus inflammatory lesions in seborrheic areas. Management is severity-based and multimodal: topical retinoids and benzoyl peroxide form the foundation, with topical and oral antibiotics, hormonal therapy in women, and oral isotretinoin reserved for more severe or refractory disease. Early, appropriate therapy can prevent permanent scarring and improve quality of life.