Acne Vulgaris — USMLE Step 2 CK Guide 2026

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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.

Key points

Acne vulgaris involves follicular hyperkeratinization, sebum, Cutibacterium acnes, and inflammation
Comedones distinguish acne from rosacea; rosacea has flushing/telangiectasia and lacks comedones
Topical retinoids are foundational for comedonal acne and maintenance; benzoyl peroxide reduces resistance when using antibiotics
Moderate inflammatory acne: topical retinoid + benzoyl peroxide +/- topical/oral antibiotics
Severe nodulocystic, scarring, or refractory acne: oral isotretinoin with strict pregnancy prevention and monitoring

Overview

Acne vulgaris is a common pilosebaceous disease driven by androgen-mediated sebum production, follicular hyperkeratinization, Cutibacterium acnes colonization, and inflammation. Lesions include open comedones (blackheads), closed comedones (whiteheads), inflammatory papules/pustules, nodules, cysts, and scars. Treatment targets lesion type and severity. Step 2 CK commonly tests contraindications and adverse effects of isotretinoin, antibiotic stewardship with benzoyl peroxide, and distinguishing acne from rosacea, perioral dermatitis, folliculitis, and drug eruptions.

Epidemiology

Acne affects most adolescents and can persist into adulthood, particularly in women. Risk factors include family history, androgen excess, occlusive cosmetics, friction/occlusion, certain medications (corticosteroids, lithium, phenytoin, isoniazid, anabolic steroids), and endocrine disorders such as PCOS when acne is severe, sudden, or accompanied by hirsutism/irregular menses. Acne can cause scarring, dyspigmentation, anxiety, depression, and social impairment.

Clinical Features

Symptoms

Facial, chest, back, or shoulder pimples with oily skin

Tender nodules or cysts in severe disease

Scarring, post-inflammatory hyperpigmentation, or psychological distress

Irregular menses, hirsutism, virilization, or sudden severe acne suggests hyperandrogenism

Signs

Open and closed comedones are the diagnostic hallmark

Inflammatory papules and pustules on face, chest, upper back

Nodules, cysts, sinus tracts, hypertrophic or ice-pick scars in severe acne

Monomorphic follicular papules/pustules without comedones suggests folliculitis or drug-induced acneiform eruption

Flushing, telangiectasias, and no comedones suggests rosacea

Investigations

First-line

Clinical diagnosis and severity gradingComedonal, mild inflammatory, moderate inflammatory, severe nodular/scarring. Assess truncal disease, scarring, dyspigmentation, and mental health

Medication and endocrine historyAsk about steroids, lithium, anticonvulsants, supplements, anabolic steroids, menstrual irregularity, hirsutism

Second-line

Pregnancy testingRequired before isotretinoin and before/while using some hormonal or teratogenic therapies

Androgen evaluationIf signs of hyperandrogenism: pregnancy test, total/free testosterone, DHEAS, 17-hydroxyprogesterone depending on presentation

Baseline labs for isotretinoinPregnancy testing, lipids, LFTs; additional monitoring depends on risk and local protocol

Specialist

CultureRare; consider gram-negative folliculitis or resistant infection if pustular eruption worsens during prolonged antibiotics

Management

AAD 2024 Acne Vulgaris Guideline

Comedonal and mild acne

Topical retinoid: adapalene, tretinoin, or tazarotene; start slowly to reduce irritation and photosensitivity
Benzoyl peroxide wash or gel for inflammatory lesions and to reduce antibiotic resistance
Noncomedogenic cleanser/moisturizer/sunscreen; avoid picking

Moderate inflammatory acne

Topical retinoid + benzoyl peroxide + topical antibiotic such as clindamycin when needed
Never use topical or oral antibiotics as monotherapy; combine with benzoyl peroxide
Oral doxycycline or minocycline for moderate-severe inflammatory/truncal acne; limit duration and transition to topical maintenance
Avoid tetracyclines in pregnancy and children <8 years; counsel photosensitivity and esophagitis prevention

Hormonal therapy

Combined oral contraceptives can help acne in appropriate female patients
Spironolactone is useful for adult female acne; avoid in pregnancy and monitor based on risk factors
Evaluate for PCOS or adrenal/ovarian tumor if severe sudden acne with virilization

Severe nodulocystic/scarring acne

Oral isotretinoin is most effective for severe nodular, scarring, or refractory acne
iPLEDGE enrollment and strict pregnancy prevention are mandatory because isotretinoin is highly teratogenic
Monitor pregnancy tests, lipids, LFTs, mood symptoms, mucocutaneous dryness; avoid tetracycline coadministration due to pseudotumor cerebri risk

Complications

Scarring: Ice-pick, rolling, boxcar, hypertrophic scars; early control prevents permanent damage
Post-inflammatory hyperpigmentation: Especially in darker skin types
Psychological morbidity: Depression, anxiety, social withdrawal, suicidality risk
Medication adverse effects: Tetracycline photosensitivity/esophagitis; isotretinoin teratogenicity, cheilitis, hypertriglyceridemia, hepatotoxicity
Antibiotic resistance: Reduced by limiting duration and combining with benzoyl peroxide

USMLE Step 2 CK Exam Tips

1Comedones = acne. No comedones + flushing/telangiectasia = rosacea
2Topical retinoids are first-line for comedonal acne and maintenance
3Always combine acne antibiotics with benzoyl peroxide to reduce resistance
4Oral isotretinoin is for severe nodulocystic/scarring acne and is highly teratogenic
5Isotretinoin + tetracycline increases pseudotumor cerebri risk
6Pregnancy: avoid isotretinoin, topical retinoids, tetracyclines, spironolactone; safer options include benzoyl peroxide/azelaic acid under guidance
7Sudden severe acne + hirsutism/irregular menses = evaluate hyperandrogenism/PCOS

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