Acne

At a glance

• Acne affects most adolescents and persists into adulthood in many, especially women.
• The commonest treatment failure is under-treatment: weak topicals for too short a time, or delaying isotretinoin in scarring disease.
• Topical retinoid plus benzoyl peroxide is the backbone at every severity. Antibiotics are added for a limited time, never alone.
• Isotretinoin is the only treatment that changes the course of the disease. In Australia only dermatologists and specialist physicians can prescribe it.
• Acne harms mental health regardless of how severe it looks. Ask about mood, self-harm and suicidal thoughts in every young person with acne, and again during isotretinoin.

Pathophysiology

Four processes, each with a drug that targets it:

Process	Target
Androgen-driven sebum production	Isotretinoin, COCP, spironolactone, clascoterone
Abnormal follicular keratinisation (comedones)	Retinoids, azelaic acid
Cutibacterium acnes colonisation	Benzoyl peroxide, antibiotics
Inflammation	Retinoids, antibiotics (anti-inflammatory effect), isotretinoin

Recognition

Severity	Features	Usual treatment
Comedonal	Open (blackheads) and closed (whiteheads) comedones	Topical retinoid
Mild to moderate papulopustular	Inflamed papules and pustules	Retinoid plus benzoyl peroxide, with or without topical antibiotic
Moderate to severe	Many papules and pustules, trunk involvement	Add oral doxycycline or hormonal therapy
Severe nodular (nodulocystic)	Nodules, cysts, sinus tracts	Isotretinoin
Any severity with scarring or marked distress		Consider isotretinoin early

• Acne fulminans: sudden painful ulcerating nodules with fever, arthralgia and sometimes lytic bone lesions, mostly in young men. It can be triggered by starting isotretinoin. Treat with oral prednisolone first, then introduce isotretinoin at a very low dose.
• Scarring (ice-pick, rolling, boxcar, hypertrophic) and post-inflammatory hyperpigmentation in darker skin often bother patients more than active lesions.

Causes and differentials

Secondary causes:

• Hyperandrogenism: irregular cycles, hirsutism, alopecia. Most is PCOS (see polycystic ovary syndrome); also non-classic congenital adrenal hyperplasia. Rapid virilisation (clitoromegaly, deepening voice) suggests an androgen-secreting tumour.
• Drugs: corticosteroids (monomorphic papules, no comedones), anabolic steroids, testosterone (including gender-affirming therapy), lithium, phenytoin, isoniazid, progestogen-only contraception, JAK inhibitors, and EGFR inhibitors (acneiform rash without comedones).

Differentials:

Condition	Distinguishing features
Rosacea	No comedones; flushing, telangiectasia, central face, older patients
Perioral dermatitis	Small papules around mouth and nose, sparing the lip border; often after topical steroids
Malassezia folliculitis	Itchy monomorphic papules on chest and back; worse with antibiotics; responds to antifungals
Gram-negative folliculitis	Pustular flare after long antibiotic courses
Hidradenitis suppurativa	Nodules and sinus tracts in axillae and groin

Investigations

• None for typical acne.
• Suspected hyperandrogenism: total testosterone and SHBG, DHEAS, 17-hydroxyprogesterone, prolactin, TSH, and LH and FSH. Take a pregnancy test before any hormonal or teratogenic treatment.
• Before isotretinoin: pregnancy test, fasting lipids and LFTs. Repeat lipids and LFTs once at peak dose. AAD 2024 found routine FBC and frequent monitoring low value in healthy young people.

Management

Topical

• Retinoids: adapalene 0.1 to 0.3%, tretinoin 0.025 to 0.05%, trifarotene 0.005%. Apply at night to the whole affected area, starting alternate nights. Irritation and an early flare are common. Avoid in pregnancy.
• Benzoyl peroxide 2.5 to 5%: bactericidal with no resistance, and it bleaches fabric.
• Topical clindamycin only with benzoyl peroxide.
• Azelaic acid 15 to 20%: helps comedones and hyperpigmentation; safe in pregnancy.
• Clascoterone 1% cream (Winlevi, TGA registered; approved overseas from age 12): topical androgen receptor blocker, an option for either sex.

Oral antibiotics

• Doxycycline 50 to 100 mg daily for moderate to severe inflammatory acne. Take it upright with water (oesophagitis) and warn about photosensitivity.
• Minocycline is second line: pigmentation, drug-induced lupus, autoimmune hepatitis and DRESS.
• Always add benzoyl peroxide and a retinoid. Reassess at 3 months and stop once controlled, continuing topicals as maintenance.
• Avoid tetracyclines in pregnancy and in children under 8. Use erythromycin if an oral antibiotic is needed in pregnancy.

Hormonal (women)

• COCP: takes 3 to 6 months. Cyproterone-containing pills (2 mg cyproterone, 35 µg ethinylestradiol) work well but carry higher VTE risk, so they aren't first line.
• Spironolactone 50 to 100 mg daily (off-label): useful for jawline and adult female acne. It needs reliable contraception; potassium monitoring isn't needed in healthy young women.

Isotretinoin

• Indications: severe nodular acne, acne with scarring, or acne that has failed an adequate trial of oral antibiotics or causes major distress. The PBS subsidises it for severe cystic acne unresponsive to other therapy.
• Prescriber restriction: dermatologists and specialist physicians only (Poisons Standard Appendix D). An application to extend initiation to GPs with advanced RACGP or ACRRM qualifications drew an interim decision not to change it from the TGA delegate on 5 November 2026, citing teratogenicity, the lack of proposed training and monitoring safeguards, and the risk of low-engagement telehealth prescribing. Submissions close 4 December 2026 and the final decision is pending. GPs can continue treatment a specialist has started. Teledermatology helps rural and remote patients reach a prescriber.
• Dose: the standard is 0.5 to 1 mg/kg/day. Many Australian dermatologists start low (for example 10 to 20 mg daily) and escalate, or use low-dose courses for months, which reduces side effects at some cost to relapse.
• Teratogen: 20 to 35% of exposed pregnancies have major malformations. Effective contraception (ideally a long-acting reversible method) from 1 month before until 1 month after the last dose, with a negative pregnancy test before starting and regular tests during treatment.
• Common adverse effects: cheilitis (almost universal), dry skin and eyes, epistaxis, photosensitivity, myalgia, and an early flare.
• Laboratory: hypertriglyceridaemia (pancreatitis risk when markedly raised) and raised transaminases.
• Serious adverse effects: drug-induced (secondary) intracranial hypertension, or pseudotumour cerebri (headache, visual change, especially with tetracyclines), reduced night vision, and mood change.
• TGA safety update (April 2025): after a 2024 review, the TGA required stronger warnings about depression, psychosis, suicidal ideation and sexual dysfunction (erectile dysfunction, reduced libido, vulvovaginal dryness), which may persist after stopping. Assess mental health, family psychiatric history and baseline sexual function before starting, monitor for mood change and sexual disorders at every visit (particularly in adolescents), and stop if they occur. Therapeutic Guidelines added this advice in September 2025.
• Other advice: don't donate blood during treatment or for a month after, avoid vitamin A supplements, and be cautious with waxing and laser resurfacing.

Acne and mental health

• Acne is linked with depression, anxiety, social withdrawal, poor self-esteem and suicidal ideation. Distress often doesn't match the clinical grade, so ask the patient.
• Screen: a HEADSS psychosocial assessment for adolescents, and PHQ-9 (or PHQ-A) for depression. Ask directly about self-harm and suicidal thoughts.
• Body dysmorphic disorder: preoccupation with minimal acne, mirror checking and skin picking. Refer to mental health; isotretinoin rarely satisfies.
• Effective acne treatment improves mood. Huang and Cheng's 2017 meta-analysis found depressive symptoms fell during isotretinoin, with no rise in depression. Tan et al. (JAMA Dermatology, 2024) found a pooled absolute risk of suicide attempt under 0.5% in isotretinoin users and no excess psychiatric risk compared with people not taking it.
• That reassurance is population-level. A minority have idiosyncratic mood change, which is why the TGA wants individual assessment and monitoring.
• Referral pathways: headspace for people aged 12 to 25, a GP mental health treatment plan, and crisis services (Lifeline 13 11 14) for acute risk.

Special populations

• Pregnancy: azelaic acid, benzoyl peroxide and topical clindamycin with benzoyl peroxide are acceptable. Avoid all retinoids (including topical), tetracyclines and spironolactone.
• Trans men on testosterone: acne peaks in the first year. Treat as usual; isotretinoin is appropriate for severe disease.
• PCOS: treat the acne and screen for metabolic risk.

Pitfalls

• Topical or oral antibiotics without benzoyl peroxide, or antibiotic courses that run for a year.
• Doxycycline with isotretinoin (intracranial hypertension).
• Stopping topicals after 4 weeks because "nothing is working". Retinoids take 8 to 12 weeks.
• Waiting for nodulocystic acne to scar before referring for isotretinoin.
• Missing an androgen-secreting tumour in a woman with sudden severe acne and virilisation.
• Starting isotretinoin or spironolactone without discussing contraception.
• Not asking about mood because the acne "doesn't look bad".