The basic cause of acne remains unknown, but its manifestations are thought to be the product of four pathogenic events: 1) increased sebum production fueled by androgenic stimulation in the pubertal period; 2) obstruction of the pilosebaceous unit due to an abnormal keratinization process; 3) proliferation of Propionibacterium acnes, an anaerobic diptheroid normally residing in pilosebaceous follicles; and 4) inflammation that is mediated both by the action of chemotactic factors and various enzymes, and initiated in part by the interaction of P. acnes with toll-like receptors. Impaction of the pilosebaceous follicle gives rise to the microcomedo that is thought to be the precursor lesion of acne.