The primary sites of acne are the face, chest, shoulders, and back. Lesions consist of open comedones (whiteheads), closed comedones (blackheads), pustules, erythematous papules, and deeper nodules (cysts).

One type of lesion may predominate, but a variety often are found in various phases of development.

When eruptive inflammatory acne lesions are all in the same stage of development, a common cause is systemic corticosteroid administration in the preceding few weeks or months.

The severity can range from mild acne with only comedones to severe nodular acne with a marked potential for disfiguring scars.

Patients with severe acne often do not appreciate the severity of the scarring because they have not seen their noninflamed faces in months to years.

The scarring process also may embed follicular epithelium remnants in the dermis, leading to the development of epidermoid cysts.

A common form of acne - acne excorieé - is caused by picking of facial lesions or perceived facial lesions. The physical examination shows excoriated, crusted lesions with few, if any, primary comedones or inflammatory lesions.