Acneiform dermatoses are follicular eruptions. The initial lesion is inflammatory, usually a papule or pustule. Comedones are later secondary lesions, a sequel to encapsulation and healing of the primary abscess. The earliest histological event is spongiosis, followed by a break in the follicular epithelium. The spilled follicular contents provokes a nonspecific lymphocytic and neutrophilic infiltrate. Acneiform eruptions are almost always drug induced. Important clues are sudden onset within days, widespread involvement, unusual locations (forearm, buttocks), occurrence beyond acne age, monomorphous lesions, sometimes signs of systemic drug toxicity with fever and malaise, clearing of inflammatory lesions after the drug is stopped, sometimes leaving secondary comedones. Other cutaneous eruptions that may superficially resemble acne vulgaris but that are not thought to be related to it etiologically are due to infection (e.g. gram-negative folliculitis) or unknown causes (e.g. acne necrotica or acne aestivalis).