Lucan · Conditions

Acne vulgaris

Australian guidance: eTG Dermatology — Acne + RACGP

1. Definition and epidemiology

Acne vulgaris is a chronic inflammatory disease of the pilosebaceous unit, characterised by comedones, papules, pustules, nodules, and cysts affecting sebaceous follicle-rich skin. It is the most common skin condition in Australia, affecting approximately 85% of adolescents between the ages of 15 and 24, with significant rates of persistent adult acne particularly in women. Scarring and psychological morbidity, including depression and impaired quality of life, are recognised sequelae that justify timely and adequate treatment.

2. Pathophysiology

Per Robbins Ch 25, four interrelated processes drive acne vulgaris: sebaceous gland hyperactivity driven by androgenic stimulation, follicular epidermal hyperproliferation producing impaction of the follicular canal, colonisation by Cutibacterium acnes (formerly Propionibacterium acnes) within the obstructed follicle, and a resultant host inflammatory response. Androgens, particularly dihydrotestosterone generated locally within sebocytes via 5-alpha reductase, upregulate sebum production. The excess sebum combines with abnormally adherent keratinocytes in the follicular infundibulum to form a microcomedone, the precursor lesion invisible to the naked eye. As the plug enlarges it produces either an open comedone (blackhead, in which oxidised melanin darkens the keratin plug through the patent follicular opening) or a closed comedone (whitehead). C. acnes, a gram-positive anaerobe and commensal of the pilosebaceous unit, proliferates within the lipid-rich environment and releases lipases, proteases, and chemotactic factors that attract neutrophils and activate toll-like receptor 2 signalling on macrophages, driving the conversion of a non-inflammatory comedone into an inflammatory papule, pustule, or nodule. Rupture of a severely distended follicle into the dermis produces the foreign body granulomatous response that underlies deep nodules and cysts, and ultimately scarring.

3. Clinical presentation and diagnostic criteria

Acne vulgaris is a clinical diagnosis. The distribution is characteristically on the face (particularly forehead, cheeks, and chin), chest, and upper back, corresponding to the density of sebaceous follicles. Lesions are classified by morphology: non-inflammatory lesions (open and closed comedones) and inflammatory lesions (papules, pustules, nodules, and cysts or pseudocysts). Severity is graded as mild (predominantly comedones with a few papules and pustules), moderate (multiple papules and pustules, few nodules, limited to face), or severe (extensive inflammatory lesions, nodules and cysts, involvement of trunk, significant risk of scarring). The Global Acne Grading System (GAGS) and the Investigator Global Assessment (IGA) scale are used in clinical trials. History should establish age of onset, menstrual cycle association, exacerbating factors (cosmetics, diet, medications), family history, prior treatments, and psychological impact.

4. Investigations and AU-specific cutoffs

Acne vulgaris generally requires no laboratory investigations for the diagnosis itself. Investigations are indicated in selected circumstances:

Androgen excess workup is required when acne is sudden in onset, severe, or treatment-resistant, or is accompanied by hirsutism, oligomenorrhoea, or signs of virilisation. Request total and free testosterone, dehydroepiandrosterone sulphate (DHEAS), sex hormone-binding globulin (SHBG), and lutenising hormone to follicle-stimulating hormone (LH:FSH) ratio to screen for polycystic ovary syndrome (PCOS) and congenital adrenal hyperplasia (CAH). Late-onset CAH is confirmed by early morning 17-hydroxyprogesterone with an adrenocorticotrophic hormone (ACTH) stimulation test if the basal value is elevated.

Before initiating isotretinoin, baseline full blood count, fasting lipids, liver function tests (LFTs), and a pregnancy test (serum beta-human chorionic gonadotropin, beta-hCG) are mandatory. The eTG recommends repeating LFTs and fasting lipids at 4 to 6 weeks and then every 3 months. Pregnancy must be excluded at each monthly dispensing visit under the iPLEDGE-equivalent Australian prescribing framework, with two forms of effective contraception required for the duration of treatment and one month post-cessation.

5. Management

Management follows a stepwise approach based on severity, guided by eTG Dermatology and RACGP acne guidelines. The overarching principle is to target as many of the four pathogenic factors as possible with the minimum number of agents.

Mild acne: topical retinoid (adapalene 0.1% gel or tretinoin 0.025% to 0.05% cream) is first-line monotherapy for comedonal acne. Topical benzoyl peroxide (BPO) 2.5% to 5% gel or wash is first-line for inflammatory acne and is recommended in combination with any topical antibiotic to suppress antibiotic resistance. Fixed-dose combination products (adapalene plus BPO, or clindamycin plus BPO) improve adherence and address resistance.

Moderate acne: add a topical antibiotic (clindamycin 1% or erythromycin 2%) to the retinoid, always combined with BPO. When topical therapy is inadequate after 8 to 12 weeks, escalate to oral antibiotics: doxycycline 50 to 100 mg daily is preferred over minocycline due to a comparable efficacy profile and lower risk of adverse effects including drug-induced lupus and pigmentation. Limit oral antibiotic courses to 3 months where possible to minimise resistance selection, and always co-prescribe BPO.

Severe or treatment-resistant acne: oral isotretinoin is the definitive therapy. The eTG recommends cumulative dosing of 120 to 150 mg/kg for optimal long-term remission. In women with PCOS-associated acne, the combined oral contraceptive pill (OCP) with anti-androgenic progestogens (cyproterone acetate plus ethinyloestradiol, or spironolactone off-label) is an effective adjunct. Intralesional triamcinolone acetonide 2.5 to 5 mg/mL is useful for rapid reduction of individual nodules or cysts.

6. Pharmacology and AU PBS notes

Topical agents are generally not PBS-listed and are purchased over the counter or on private prescription. Benzoyl peroxide products (e.g. Benzac AC) are available without prescription. Topical clindamycin 1% (Clindatech, Dalacin T) and adapalene 0.1% (Differin) are available without prescription as of 2024 rescheduling in Australia.

Oral doxycycline 50 mg and 100 mg (Doryx, Doxine, generic) is PBS-listed for acne under Streamlined Authority Code 9204 for moderate to severe acne in patients 12 years and over; maximum 3 months per PBS approval cycle, extendable on clinical grounds.

Oral isotretinoin (Oratane, Absorbica) is a Section 85 PBS benefit under Authority Required (STREAMLINED) listing for severe acne unresponsive to other treatments or at risk of significant scarring. It must be initiated by a specialist (dermatologist) or a GP with appropriate experience; dispensing requires monthly prescriptions no more than 30 days supply. The PBS code is 1767G. Standard dosing begins at 0.5 mg/kg/day and increases to 1 mg/kg/day as tolerated, targeting a cumulative dose of 120 to 150 mg/kg.

Cyproterone acetate 2 mg plus ethinyloestradiol 35 micrograms (Diane-35) is PBS-listed for severe acne associated with androgen excess in women; Authority Required. Spironolactone 25 to 100 mg daily is used off-label without PBS subsidy for hormonal acne in women.

7. Complications and monitoring

Scarring is the most clinically important complication and is the primary driver of early aggressive treatment. Scarring subtypes include ice-pick, rolling, and boxcar scars; hypertrophic or keloid scars are less common and influenced by Fitzpatrick skin type. Post-inflammatory hyperpigmentation (PIH) is particularly prevalent in individuals with Fitzpatrick types IV to VI, as is common in First Nations, South-East Asian, South Asian, Middle Eastern, and African-Australian patients.

Psychological morbidity including depression, anxiety, and suicidal ideation is well-documented. During isotretinoin therapy, the eTG mandates monthly monitoring for mood change; patients and carers should be counselled that depression or suicidal ideation must prompt immediate contact with the prescriber or emergency services.

Isotretinoin teratogenicity (Pregnancy Category X in Australia) requires mandatory contraception and monthly pregnancy testing. Monitoring during isotretinoin includes fasting lipids and LFTs at baseline, 4 to 6 weeks, and then 3-monthly. Antibiotic resistance surveillance: antibiotic monotherapy without concurrent BPO should be avoided; the eTG recommends periodic review at 3 months to assess treatment response and avoid prolonged courses.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.