Acne Vulgaris: Clinical Presentation, Severity Grading, and Pathophysiology

Lesion Types

Acne vulgaris manifests as open comedones (blackheads), closed comedones (whiteheads), inflammatory papules, pustules, and nodules, primarily on the face and trunk, and may lead to pain, erythema, hyperpigmentation, and scarring. – American Academy of Dermatology 1
Comedones are the foundational lesions caused by follicular hyperkeratinization and obstruction of the sebaceous duct. – American Academy of Dermatology 1
Open comedones are dilated follicular openings filled with dark keratin plugs that are visible on the skin surface. – American Academy of Dermatology 1
Closed comedones are obstructed follicles without a visible surface opening, appearing as smooth white papules. – American Academy of Dermatology 1
Papules are small, raised, erythematous lesions that arise from perifollicular inflammation. – American Academy of Dermatology 1
Pustules are papules that contain a purulent (neutrophil‑rich) center, reflecting an acute inflammatory response around the hair follicle. – American Academy of Dermatology 1
Nodules are deep, painful, solid lesions extending into the dermis and represent the most severe form of inflammatory acne. – American Academy of Dermatology 1, 2

Truncal acne (chest and back) is characterized by a thicker stratum corneum, lower sebaceous gland density, and distinct site‑specific microbiota compared with facial acne. – American Academy of Dermatology 1

Post‑inflammatory erythema can persist after resolution of active lesions. – American Academy of Dermatology 1
Facial scarring is observed in approximately 63 % of adult acne patients, underscoring the need for early and, when appropriate, aggressive therapy such as oral isotretinoin. – American Academy of Dermatology 2

The American Academy of Dermatology consensus defines a 5‑point ordinal severity scale (0 = clear, 1 = almost clear, 2 = mild, 3 = moderate, 4 = severe). – American Academy of Dermatology 1, 3
Grade 0 (clear) and Grade 1 (almost clear) correspond to the absence of active lesions or only minimal residual lesions. – American Academy of Dermatology 2
Grade 2 (mild) reflects limited lesion counts with predominantly comedonal disease and occasional inflammatory papules. – American Academy of Dermatology 4
Grade 4 (severe) denotes extensive inflammatory disease with numerous papules, pustules, nodules, and a high risk of scarring. – American Academy of Dermatology 2

The Investigator Global Assessment (IGA) is the most widely used severity grading tool in the United States and demonstrates good concordance between clinician and patient assessments. – American Academy of Dermatology 1, 5
An optimal acne grading system should capture primary lesion types, total lesion counts, anatomical extent, and regional involvement while possessing robust psychometric properties. – American Academy of Dermatology 1

Acne pathogenesis is multifactorial, involving follicular hyperkeratinization, colonization by Cutibacterium acnes, and complex innate and adaptive immune inflammatory pathways. – American Academy of Dermatology 1, 4

The American Academy of Dermatology (AAD) guidelines state that there is no evidence that exposure to asbestos, fuel oil, diesel fuels, per‑ and polyfluoroalkyl substances (PFAS), or aqueous film‑forming foam (AFFF) contributes to the development or exacerbation of acne vulgaris【6】【7】.

According to AAD recommendations, acne pathogenesis is multifactorial—driven by follicular hyperkeratinization, Cutibacterium acnes colonization, sebum production, innate and adaptive immune inflammation, neuroendocrine influences, and genetic as well as non‑genetic factors—but does not involve the aforementioned environmental exposures【6】.
The AAD identifies increasing adolescent age, a positive family history of acne, and an oily skin phenotype as the primary recognized risk factors for acne development【6】【7】.

When acne occurs in individuals with occupational exposure to the listed agents, treatment should follow standard AAD‑based acne protocols rather than attributing disease activity to the exposure【6】【8】【9】.
The AAD provides strong recommendations for first‑line pharmacologic therapy, including benzoyl peroxide, topical retinoids, topical antibiotics, and oral doxycycline【8】【9】.
Combining topical agents that act via different mechanisms is strongly recommended to maximize therapeutic efficacy【9】.
Oral isotretinoin receives a strong recommendation for patients with severe acne, significant psychosocial impact, scarring risk, or failure of conventional topical and oral regimens【8】.