Acne is an inflammation of the pilosebaceous units of certain body areas, predominantly the face, and to a lesser extent the trunk and buttocks, that manifests as comedones, papulopustules (pimples), or nodules and cysts (nodulocystic). Pitted, depressed, or hypertrophic scars may follow all types but especially nodulocystic. Acne results from a change in the keratinization pattern in the pilosebaceous unit, with keratinous material becoming more dense and blocking secretion of sebum. These kertain plugs are called comedomes. Androgens stimulate sebaceous glands to produce larger amounts of sebum which contribute to formation of comedomes. Bacteria on the skin produce proinflammatory mediators which cause an inflammatory response in the pilosebaceous unit and further contribute to formation of comedomes.