Acne Lesion Description
Acne vulgaris is a chronic inflammatory dermatosis characterized by both noninflammatory lesions (open and closed comedones) and inflammatory lesions (papules, pustules, and nodules), all affecting the pilosebaceous follicles primarily on the face, chest, upper back, and other sebum-rich areas. 1
Noninflammatory Lesions
- Open comedones (blackheads): These are dilated follicular openings filled with keratin and sebum, appearing dark due to oxidation and melanin, not dirt 1, 2
- Closed comedones (whiteheads): These are follicles obstructed beneath the skin surface with accumulated keratin and sebum, appearing as small flesh-colored or white papules 1, 2
Inflammatory Lesions
- Papules: Small (typically <5mm), erythematous, raised, tender bumps representing inflamed pilosebaceous units without visible purulent material 1, 2
- Pustules: Raised lesions containing visible purulent material (white or yellow center) surrounded by erythema, indicating active inflammation and immune response 1, 2
- Nodules (also called cysts): Large (>5mm), deep-seated, painful, indurated lesions extending into the dermis and subcutaneous tissue, representing severe inflammation of the pilosebaceous unit 1
Distribution and Anatomic Sites
- Lesions predominantly affect areas with high concentrations of pilosebaceous glands: face (most common), chest, upper back, neck, and shoulders 3, 4
- The face is the primary site in most patients, though truncal involvement occurs frequently, particularly in males 1, 3
Secondary Changes and Sequelae
- Post-inflammatory hyperpigmentation: Darkened macules or patches remaining after inflammatory lesions resolve, particularly common in darker skin types 1, 5
- Post-inflammatory erythema: Persistent redness at sites of previous inflammatory lesions 1, 4
- Scarring: Permanent textural changes including atrophic (ice-pick, rolling, boxcar) or hypertrophic scars resulting from severe inflammation and tissue destruction 1, 3, 4
Clinical Morphology Patterns
Acne presents as a pleomorphic (multiple lesion types simultaneously present) disorder, distinguishing it from monomorphic conditions like pityrosporum folliculitis, which requires different treatment. 6, 2
Important Clinical Pitfall
- Monomorphic truncal papules and pustules that are uniform in appearance suggest pityrosporum folliculitis (fungal acne), not acne vulgaris, and require microbiologic testing and antifungal therapy rather than standard acne treatment 5, 6
- True acne vulgaris displays polymorphic lesions with comedones as a hallmark feature, whereas fungal folliculitis lacks comedones entirely 6
Inflammatory Nature
Despite traditional classification of comedones as "noninflammatory," current evidence demonstrates that acne is fundamentally an inflammatory disease even before clinical lesions appear, with inflammation present at the microscopic level in all stages. 7, 8