Acne vulgaris (commonly called Acne) is a skin disease, caused by changes in the pilosebaceous units (skin structures consisting of a hair follicle and its associated sebaceous gland). Severe acne is inflammatory, but acne can also manifest in noninflammatory forms. Acne lesions are commonly referred to as pimples, spots, or zits.

Acne is most common during adolescence, affecting more than 85% of teenagers, and frequently continues into adulthood. For most people, acne diminishes over time and tends to disappear, or at least decrease, after one reaches his or her early twenties. There is, however, no way to predict how long it will take for it to disappear entirely, and some individuals will continue to suffer from acne decades later, into their thirties and forties and even beyond.

The term acne comes from a corruption of the Greek άκμή (acme in the sense of a skin eruption) in the writings of Aëtius Amidenus. The vernacular term bacne or backne is often used to indicate acne found specifically on one's back.