An eruption, predominantly of the face, upper back, and chest, composed of comedones, cysts, papules, and pustules onan inflammatory base; the condition occurs in a majority of people during puberty and adolescence, due to androgenicstimulation of sebum secretion, with plugging of follicles by keratinization, associated with proliferation ofPropionibacterium acnes. Syn: acne simplex, simple acne.