Acne Vulgaris
Common inflammatory skin condition affecting ~85% of adolescents and young adults. Caused by a combination of excess sebum production, follicular hyperkeratinisation, Cutibacterium acnes colonisation, and inflammation. Presents with comedones, papules, pustules, and in severe cases, nodules and cysts. Treatment is stepwise from topical retinoids/benzoyl peroxide to oral isotretinoin for severe/scarring disease.
Key Facts
Prevalence: ~85% of 12–24-year-olds; ~12% of adult women have persistent acne Four pathogenic factors: excess sebum (androgen-driven), follicular hyperkeratinisation, C. acnes proliferation, inflammation Comedones: open (blackheads) and closed (whiteheads) — hallmark of acne; distinguish from rosacea (no comedones) Topical retinoids (tretinoin, adapalene): first-line for comedonal acne — normalise follicular keratinisation Benzoyl peroxide 5%: bactericidal against C. acnes; does NOT cause antibiotic resistance; combine with topical retinoid Oral isotretinoin (Roaccutane): 0.5–1mg/kg/day for 16–24 weeks; only treatment that addresses ALL four pathogenic factors; teratogenic — iPLEDGE programme (or UK equivalent) mandatory pregnancy prevention COCP (co-cyprindiol/Dianette): anti-androgenic; useful for females with hormonal acne; increased VTE risk NICE CG (2021): recommends fixed-combination topicals as first-line (adapalene + benzoyl peroxide)
Overview
Key Facts
Acne is not just a cosmetic condition — it causes significant psychological distress and can lead to permanent scarring. Early effective treatment prevents both physical and psychological sequelae.
Epidemiology
- Affects ~85% of adolescents (12–24 years)
- Adult female acne increasingly recognised (~12% of women >25 years)
- Male:female ~1:1 in adolescence; female predominance in adults
Aetiology
- Androgen-driven sebum excess: DHT stimulates sebaceous glands
- Follicular hyperkeratinisation: abnormal desquamation → microcomedone formation
- C. acnes colonisation: lipophilic anaerobe; produces lipases and pro-inflammatory mediators
- Inflammation: innate immune activation (TLR2) → cytokines → papules, pustules, nodules
Pathophysiology
- Testosterone → 5-alpha reductase → DHT → sebaceous gland hypertrophy → excess sebum
- Abnormal keratinocyte desquamation in follicular infundibulum → microcomedone (precursor of all acne lesions)
- C. acnes proliferates in sebum-rich, anaerobic follicle → activates innate immunity via TLR2
- Severe inflammation → follicle rupture → nodules, cysts → scarring
Clinical Presentation
Non-Inflammatory
- Open comedones (blackheads): dilated pore with oxidised melanin/sebum
- Closed comedones (whiteheads): small flesh-coloured papules
Inflammatory
- Papules: small raised erythematous lesions
- Pustules: papules with visible pus
- Nodules: deep, painful, >5mm
- Cysts: deep fluctuant lesions — risk of scarring
Distribution
- Face (99%), back (60%), chest (15%)
Scarring
- Ice-pick, rolling, boxcar scars
- Post-inflammatory hyperpigmentation (especially darker skin)
Red Flags
- Sudden severe acne in pre-pubertal child (evaluate for androgen excess)
- Acne with virilisation in females (PCOS, adrenal tumour)
- Severe nodulo-cystic acne with systemic symptoms (acne fulminans)
- Significant psychological distress/suicidal ideation
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Rosacea | No comedones, central face, telangiectasia, age >30 | Clinical |
| Perioral dermatitis | Perioral/perinasal papulopustules, no comedones | Clinical |
| Folliculitis | Monomorphic pustules centred on hair follicles | Swab for MC&S |
| Milia | Tiny white cysts (keratin-filled), no inflammation | Clinical |
| Drug-induced acne | Monomorphic, temporal drug relationship (steroids, lithium) | Drug history |
Diagnosis / Investigation
Clinical Diagnosis
- History and examination sufficient in most cases
- Grade severity: mild (comedones ± few papules/pustules), moderate (papulopustular), severe (nodulo-cystic/scarring)
If Indicated
- Hormonal screen (females): if PCOS suspected — testosterone, SHBG, DHEAS, LH, FSH, prolactin
- Pelvic USS: if PCOS features
- Pre-isotretinoin: FBC, LFTs, fasting lipids, pregnancy test (before, during, 1 month after)
- Psychiatric assessment: if significant mood disturbance before/during isotretinoin
Management
Mild (Comedonal/Few Papulopustules)
- First-line: fixed-combination adapalene 0.1% + benzoyl peroxide 2.5% (Epiduo) OD
- Alternative: topical retinoid alone (adapalene, tretinoin) or benzoyl peroxide 5% alone
Moderate (Papulopustular)
- Fixed-combination topical + consider oral antibiotics
- Oral antibiotics: lymecycline 408mg OD or doxycycline 100mg OD for 3 months maximum
- ALWAYS combine oral antibiotic with topical retinoid/BPO (prevents resistance)
- Do NOT use topical and oral antibiotics together
Severe (Nodulo-Cystic/Scarring) or Treatment-Resistant
- Oral isotretinoin 0.5–1mg/kg/day for 16–24 weeks (cumulative dose 120–150mg/kg)
- Teratogenic: mandatory pregnancy prevention programme (2 forms of contraception or abstinence; monthly pregnancy tests)
- Side effects: dry skin/lips (universal), myalgia, raised lipids, raised LFTs, mood changes (monitor)
- Monitor: LFTs and fasting lipids at baseline, 1 month, then 3-monthly
Females with Hormonal Acne
- COCP: co-cyprindiol (Dianette) — anti-androgenic; increased VTE risk (limit to 3–4 courses)
- Spironolactone 50–200mg OD: off-label; anti-androgen; useful in adult female acne
Referral Criteria
- Dermatology: severe/scarring acne, treatment failure with oral antibiotics, consideration for isotretinoin
- Urgent: acne fulminans, severe psychological distress
Prognosis
- Most adolescent acne resolves by mid-20s
- ~12% of women have persistent adult acne
- Isotretinoin: ~80% achieve long-term remission after one course; ~20% need second course
- Scarring: permanent without treatment; early effective therapy prevents
- Psychological impact: depression, anxiety, reduced self-esteem — comparable to chronic disease
Other Relevant Information
Acne Treatment Ladder
| Severity | First-Line | Second-Line |
|---|---|---|
| Mild comedonal | Topical retinoid ± BPO | Azelaic acid |
| Mild papulopustular | Adapalene + BPO | + oral antibiotic |
| Moderate | Oral antibiotic + topical retinoid + BPO | Hormonal (females) |
| Severe/scarring | Oral isotretinoin | Repeat course |
Isotretinoin Key Points
| Parameter | Detail |
|---|---|
| Dose | 0.5–1mg/kg/day |
| Duration | 16–24 weeks |
| Cumulative dose | 120–150mg/kg |
| Pregnancy test | Before, monthly, 1 month after |
| Monitoring | LFTs, fasting lipids |