Different types of Acne Vulgaris: A: Cystic acne on the face, B: Subsiding tropical acne of trunk, C: Extensive acne on chest and shoulders. Acne Vulgaris is an inflammatory disease of the skin, caused by changes in the pilosebaceous units (skin structures consisting of a hair follicle and its associated sebaceous gland). Acne lesions are commonly referred to as pimples, spots, plooks or "zits". Acne develops as a result of blockages in follicles. Hyperkeratinization and formation of a plug of keratin and sebum (a microcomedo) is the earliest change. Enlargement of sebaceous glands and an increase in sebum production occur with increased androgen (DHEA-S) production at adrenarche. The microcomedo may enlarge to form an open comedo (blackhead) or closed comedo (whitehead). In these conditions the naturally occurring largely commensual bacteria Propionibacterium acnes can cause inflammation, leading to inflammatory lesions (papules, infected pustules, or nodules) in the dermis around the microcomedo or comedo, which results in redness and and may result in scarring or hyperpigmentation.[1] Acne is most common during adolescence, affecting more than 85% of teenagers, and frequently continues into adulthood. [2] 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.[3] The term acne comes from a corruption of the Greek ??µ? (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.[citation needed]