Acne vulgaris
Exam Tips
- Comedones are the key discriminator: if no comedones, reconsider diagnosis.
- Grade by lesion type and extent (mild comedonal, moderate papulopustular, severe nodulocystic/scarring) to guide treatment step-up.
- Do not use topical or oral antibiotics alone; combine with benzoyl peroxide and limit antibiotic duration (typically 12 weeks).
- In women with acne plus irregular periods/hirsutism, think PCOS/hyperandrogenism and investigate appropriately.
- Know red flags for urgent specialist input: acne fulminans (fever, arthralgia, ulcerative lesions), rapidly progressive severe nodulocystic acne, or early scarring.
- For any retinoid discussion, state teratogenic risk and pregnancy-prevention requirements explicitly.
Definition
Acne vulgaris is a chronic inflammatory disorder of the pilosebaceous unit that most commonly affects the face, chest, and back in adolescents and young adults. It is defined clinically by comedones (open or closed) with variable inflammatory lesions such as papules, pustules, nodules, or cysts, and may lead to scarring and pigmentary change.
Pathophysiology
Acne develops through four interacting mechanisms: follicular hyperkeratinization causing microcomedone formation, androgen-driven excess sebum production, proliferation of Cutibacterium acnes within sebum-rich follicles, and a local inflammatory response. Follicular rupture and release of pro-inflammatory mediators (including innate immune cytokine pathways such as IL-1 signaling) drive papules/pustules and, in deeper disease, nodules/cysts with sinus formation. Genetic susceptibility, hormonal fluctuation (including menstrual flares), and high glycaemic dietary patterns can amplify these pathways and persistence of disease.
Risk Factors
- Adolescence/puberty (peak prevalence in ages 12-24)
- Family history of acne (including severe acne)
- Male sex for more severe adolescent disease; female sex for persistent adult acne
- Androgen excess states (e. g, polycystic ovary syndrome, hyperandrogenism)
- Menstrual-cycle hormonal fluctuation
- High glycaemic-load diet; possible contribution from whey/milk in some patients
- Occlusive cosmetics, pomades, and comedogenic skin products
- Drug-induced/acneiform triggers (corticosteroids, lithium, isoniazid, ciclosporin, anabolic steroids, some antiepileptics, vitamins B1/B6/B12)
Clinical Features
Symptoms
- Often asymptomatic comedonal eruption on face, chest, or back
- Tender or painful inflammatory lesions (especially nodules/cysts)
- Intermittent flares, commonly premenstrual in women
- Psychological distress: low self-esteem, anxiety, low mood, social withdrawal
Signs
- Comedones (essential for typical acne diagnosis): open blackheads and closed whiteheads
- Inflammatory papules and pustules (<5 mm)
- Nodules/cysts (>5 mm), sometimes fluctuant and painful in severe disease
- Seborrhoea in affected skin
- Post-inflammatory hyperpigmentation or hypopigmentation
- Atrophic (ice-pick/boxcar/rolling), hypertrophic, or keloid scarring
- Very severe variants: acne conglobata with sinuses; acne fulminans with ulcerative lesions and systemic upset
- Image reference: DermNet NZ acne image atlas is useful for lesion pattern recognition in exam revision
Investigations
Management
Lifestyle Modifications
- Explain chronic-relapsing course and set realistic expectations (improvement usually takes 6-8 weeks; assess response at ~12 weeks)
- Use non-comedogenic cleanser/moisturizer/sunscreen; avoid picking/squeezing to reduce scarring and post-inflammatory pigment change
- Review potential triggers: occlusive cosmetics, pomades, friction/pressure, and culprit medicines where possible
- Offer psychosocial support and actively assess mental health impact
- Discuss pregnancy potential before prescribing teratogenic agents (especially retinoids)
Pharmacological Treatment
Topical benzoyl peroxide/retinoid-based first line (mild to moderate)
- Benzoyl peroxide 2.5-5% gel once daily, increase to twice daily if tolerated
- Adapalene 0.1% gel once nightly
- Adapalene 0.1% + benzoyl peroxide 2.5% gel once nightly
- Azelaic acid 20% cream twice daily (useful if irritation or pigment concerns)
Start low/frequency-adjust for irritation; warn about dryness and photosensitivity; benzoyl peroxide bleaches fabric/hair; topical retinoids are contraindicated in pregnancy.
Topical antibiotic combinations (not monotherapy)
- Clindamycin 1% + benzoyl peroxide 5% gel once daily
- Treclin gel (clindamycin 1% + tretinoin 0.025%) once nightly
Use with benzoyl peroxide to reduce antimicrobial resistance; avoid prolonged continuous antibiotic use; avoid topical/oral antibiotic monotherapy.
Oral antibiotics for moderate-severe inflammatory acne (usually with topical non-antibiotic agent)
- Lymecycline 408 mg once daily for ~12 weeks
- Doxycycline 100 mg once daily for ~12 weeks
- Oxytetracycline 500 mg twice daily (empty stomach) for ~12 weeks
- Erythromycin 500 mg twice daily if tetracyclines unsuitable
Avoid tetracyclines in pregnancy/breastfeeding and in children under 12 years; counsel on doxycycline photosensitivity and esophagitis risk; review at 12 weeks and stop/switch to maintenance topical therapy where possible.
Hormonal therapy in women
- Co-cyprindiol (cyproterone acetate 2 mg/ethinylestradiol 35 micrograms): 1 tablet daily for 21 days of each 28-day cycle
Consider when clear androgen sensitivity or need for combined hormonal approach after standard therapy; assess VTE risk and standard combined oral contraceptive contraindications (e. g, smoking age >35, migraine with aura, prior VTE).
Specialist oral retinoid for severe/refractory or scarring acne
- Isotretinoin usually 0.5 mg/kg/day initially, titrated (often up to 1 mg/kg/day) under specialist care
Teratogenic: strict pregnancy prevention programme, baseline and follow-up monitoring (lipids/LFTs), and mental health monitoring; avoid concurrent tetracyclines (risk of intracranial hypertension). Urgent dermatology referral for acne fulminans, rapidly progressive nodulocystic acne, or significant scarring risk.
Surgical / Interventional
- Intralesional corticosteroid injection for selected large inflammatory nodules (specialist setting)
- Comedone extraction or limited drainage for fluctuant cystic lesions in selected cases
- Scar-directed procedures after active disease control (e. g, subcision, microneedling, chemical peels, laser resurfacing)
Complications
- Permanent scarring (atrophic, hypertrophic, keloid)
- Post-inflammatory hyperpigmentation or hypopigmentation (often more marked in darker skin types)
- Psychological morbidity including anxiety, depression, reduced self-esteem, and suicidality risk
- Social/educational quality-of-life impairment
- Association with metabolic comorbidities (obesity, dyslipidaemia, diabetes, hypertension, metabolic syndrome)
Prognosis
Acne usually begins around puberty and often improves after adolescence, but it can persist for years and may continue or newly present in adulthood. Severe inflammatory acne, male sex in adolescence, and delayed effective treatment increase risk of persistent disease and scarring; adult persistence is particularly common in women.
Sources & References
🏥BMJ Best Practice(1)
✅NICE Guidelines(1)
- Acne vulgaris[overview]