Acne vulgaris: high-yield one-liners for INI-CET and NEET PG

Basics and pathogenesis

• Acne vulgaris is a chronic inflammatory disorder of the pilosebaceous unit, typically beginning at puberty.
• The four key pathogenic factors are follicular hyperkeratinization, increased sebum production, Cutibacterium acnes proliferation, and inflammation.
• Microcomedone is the primary lesion of acne.
• C. acnes is the current name for Propionibacterium acnes.
• Acne favors areas with maximum sebaceous glands: face, upper chest, shoulders, and upper back.
• Androgens increase both sebaceous-gland size and sebum production.

Lesion identification

• Closed comedone = whitehead: follicular opening is closed.
• Open comedone = blackhead: black color is due to oxidized melanin and lipid material, not dirt.
• Comedones are non-inflammatory lesions; papules, pustules, nodules, and cysts are inflammatory lesions.
• A patient with acneiform eruption but no comedones is more likely to have drug-induced acne, rosacea, folliculitis, or periorificial dermatitis rather than acne vulgaris.
• Nodules are deep, painful inflammatory lesions that carry a high risk of scarring.

Important clinical variants

• Acne conglobata: severe chronic nodulocystic acne with abscesses, communicating sinus tracts, and severe scarring; commonly affects males.
• Acne fulminans: abrupt onset of painful ulcerative/nodular acne with systemic features such as fever, arthralgia, myalgia, leukocytosis, and elevated ESR.
• First-line treatment of acne fulminans is systemic corticosteroids, followed by low-dose isotretinoin after inflammation is controlled.
• Acne excoriée is acne worsened by compulsive picking, often seen in young women.
• Acne mechanica is precipitated by friction, occlusion, pressure, heat, or sweating, for example helmets, masks, tight clothing, or sports gear.
• Pomade acne occurs along the hairline and forehead due to comedogenic hair products.
• Chloracne results from exposure to halogenated aromatic hydrocarbons, classically dioxins, and produces comedones and cysts, often in postauricular and malar areas.
• Steroid acne is typically monomorphic, papulopustular, and lacks comedones.
• Malassezia folliculitis causes monomorphic pruritic follicular papules/pustules, commonly on the trunk, with no comedones.

Age-related acne

• Neonatal acne generally occurs in the first few weeks of life and is usually self-limited.
• Infantile acne starts at about 3-6 months, has true comedones, lasts longer, and may scar.
• In a child with severe acne, look for precocious puberty or androgen excess.

When to suspect hyperandrogenism

• Consider PCOS or another androgen-excess disorder in women with sudden-onset severe acne, hirsutism, irregular menses, infertility, virilization, or treatment-resistant adult acne.
• Acne associated with PCOS is often concentrated over the jawline, chin, and lower face.

Treatment one-liners

Topical agents

• Topical retinoids are first-line for comedonal acne and are also used as maintenance therapy.
• Topical retinoids are comedolytic and anti-inflammatory and normalize follicular keratinization.
• Adapalene is photostable and is generally the best-tolerated topical retinoid.
• Tazarotene is the most potent and most irritating topical retinoid and is contraindicated in pregnancy.
• Apply topical retinoids in a pea-sized quantity to the whole acne-prone area, not only on visible lesions.
• Benzoyl peroxide is bactericidal against C. acnes and does not induce bacterial resistance.
• Benzoyl peroxide may cause irritation, dryness, contact dermatitis, and bleaching of clothes/hair.
• Topical clindamycin or erythromycin should never be used alone due to resistance. Combine with benzoyl peroxide.
• Azelaic acid is useful for acne with post-inflammatory hyperpigmentation and is a useful option when pregnancy is a concern.
• Salicylic acid is keratolytic and comedolytic but less central than retinoids/BPO in standard exam algorithms.
• Dapsone gel may cause yellow-orange discoloration when used together with benzoyl peroxide.

Systemic antibiotics

• Oral antibiotics are indicated in moderate-to-severe inflammatory acne, always along with topical retinoid and/or benzoyl peroxide.
• Doxycycline is the preferred oral tetracycline in many current guidelines.
• Limit systemic antibiotics to the shortest practical duration, commonly around 12 weeks, to reduce antimicrobial resistance.
• Do not prescribe oral antibiotics as monotherapy and do not combine an oral antibiotic with the same topical antibiotic.
• Tetracyclines are contraindicated in pregnancy, breastfeeding, and children younger than 8 years.
• Doxycycline causes photosensitivity and esophagitis: take with water and remain upright.
• Minocycline causes pigmentation, drug-induced lupus, hypersensitivity syndrome, and vestibular adverse effects.
• Erythromycin is an alternative when tetracyclines cannot be used, but resistance limits its utility.

Hormonal treatment

• Combined oral contraceptives and spironolactone are useful in women with hormonally driven acne.
• Spironolactone acts as an antiandrogen and may cause menstrual irregularity, breast tenderness, and hyperkalemia.
• Spironolactone should be avoided in pregnancy because of potential antiandrogenic effects on a male fetus.

Isotretinoin: must-know facts

• Oral isotretinoin is indicated for severe nodulocystic acne, acne with scarring/major psychosocial burden, or acne refractory to standard treatment.
• Isotretinoin is the only acne drug that acts on all four major pathogenetic factors, especially by markedly reducing sebaceous-gland activity.
• Common exam cumulative-dose target: 120-150 mg/kg, although treatment is increasingly individualized clinically.
• The most frequent adverse effect is cheilitis.
• Other adverse effects: xerosis, epistaxis, dry eyes, myalgia, hypertriglyceridemia, transaminitis, and mood symptoms requiring clinical vigilance.
• Isotretinoin is highly teratogenic: pregnancy must be avoided during therapy and for at least 1 month after stopping.
• Avoid combining isotretinoin with tetracyclines because of risk of intracranial hypertension/pseudotumor cerebri.
• Avoid concomitant vitamin A supplements due to additive toxicity.
• Monitor pregnancy status in people who can conceive and commonly monitor lipids and liver enzymes during systemic treatment.
• A topical retinoid, with or without benzoyl peroxide, can be used as maintenance after isotretinoin to reduce relapse.

Complications and scars

• Acne may leave post-inflammatory erythema, post-inflammatory hyperpigmentation, atrophic scars, hypertrophic scars, and keloids.
• Atrophic scars are classified as ice-pick, boxcar, and rolling scars.
• Ice-pick scars are narrow and deep; boxcar scars have sharp vertical edges; rolling scars are broad and tethered.
• Keloidal acne scars are more common on the chest, shoulders, jawline, and back.

Rapid exam algorithm

• Comedonal acne: topical retinoid ± benzoyl peroxide.
• Mild inflammatory acne: benzoyl peroxide + topical retinoid ± topical antibiotic.
• Moderate inflammatory acne: topical retinoid + benzoyl peroxide + oral doxycycline/minocycline for limited duration.
• Severe nodular/cystic or scarring acne: oral isotretinoin.
• Acne fulminans: systemic corticosteroid first, then cautious low-dose isotretinoin.