What is acne vulgaris?

Acne Vulgaris Definition

Acne vulgaris is a chronic, inflammatory skin disease of the pilosebaceous unit that primarily presents with open or closed comedones, papules, pustules, or nodules on the face or trunk and may result in pain, erythema, hyperpigmentation, or scars. 1

Core Pathophysiologic Features

The disease involves four key pathogenic mechanisms that drive its clinical presentation:

• Follicular hyperkeratinization leads to obstruction of sebaceous follicles from abnormal keratinization of the infundibular epithelium 2
• Androgen-stimulated sebum overproduction increases sebaceous gland secretion, creating an environment for bacterial proliferation 2, 3
• Microbial colonization by Cutibacterium acnes (formerly Propionibacterium acnes) within the pilosebaceous unit promotes inflammation through production of biologically active mediators 2, 4
• Inflammatory cascade with release of inflammatory mediators in the perifollicular region, involving neutrophil and macrophage infiltration 2, 3

Clinical Presentation Spectrum

Acne manifests across a spectrum of severity:

• Comedonal lesions include open comedones (blackheads) and closed comedones (whiteheads) representing the non-inflammatory form 1
• Inflammatory lesions progress to papules, pustules, and nodules when follicular rupture and immune response occur 1, 2
• Sequelae include post-inflammatory erythema, hyperpigmentation, and scarring that can persist beyond active disease 1

Epidemiology and Disease Burden

• Acne affects approximately 85% of adolescents but can occur across most age groups and persist into adulthood 1
• Over 50 million people in the United States have acne, making it the eighth most prevalent disease globally 1
• The condition affects 9.4% of the global population based on 2010 data 1

Impact on Quality of Life

The psychosocial burden of acne is substantial and should not be underestimated:

• Health-related quality of life impact is comparable to chronic diseases such as asthma, psoriasis, and arthritis 5
• Acne significantly affects emotional functioning, social relationships, daily activities, sleep, school, and work 1, 5
• The condition is associated with higher risk of stigma, bullying, depression, anxiety, low self-esteem, and suicidal ideation 5
• In 2013, acne led to $846 million in medical costs and $398 million in lost productivity for patients and caregivers in the United States 1

Severity Classification

The American Academy of Dermatology recommends using a 5-point ordinal scale (0-4: clear, almost clear, mild, moderate, and severe) to quantify acne severity in routine clinical practice 1, 5:

• Mild acne is characterized by a predominance of comedones (open or closed) 5
• Moderate acne involves mixed comedonal and inflammatory lesions (papules and pustules) 6
• Severe acne presents with nodules, extensive inflammatory lesions, or evidence of scarring 6

The Investigator Global Assessment (IGA) is the most commonly used grading system in the United States and demonstrates good agreement between clinician and patient ratings 1, 5

Important Clinical Distinctions

When evaluating acne-like presentations, consider these differential diagnoses:

• Gram-negative folliculitis can develop after prolonged broad-spectrum antibiotic therapy and requires bacterial culture for diagnosis 7
• Pityrosporum folliculitis (fungal acne) worsens with antibiotics and requires antifungal treatment 6
• Pseudomonas folliculitis (hot tub folliculitis) is distinguished by water exposure history and P. aeruginosa on culture 7