Inflammatory disease of the oil glands of the skin. Acne vulgaris, probably the most frequent chronic skin disorder, results from an interplay of hereditary factors, hormones, and bacteria, beginning in the teen years when overactive sebaceous glands are stimulated by high levels of androgens. Its primary lesion, the blackhead, may be open or closed; it consists of a plug of skin oil (sebum), cell debris, and microorganisms in a hair follicle. Acne has four grades of severity, with increasing degrees of spread, inflammation, pustule formation, and scarring. Methods of treatment vary from skin medication to antibiotics and hormones; many cases eventually resolve spontaneously.