It is characterized by the presence of blackheads, pimples, cysts, and scars. The primary manifestations of the disease result from irritation and inflammation of the affected hair follicles. Acne affects most teenagers to some degree, and tends to be worse in boys. Despite its association with the teen years, acne can persist into, or begin in, adulthood. Acne blemishes most commonly occur on the oily areas of the face, neck, upper torso, and upper arms.
Hair grows, and is contained in, narrow tube-like structures with bulbous bottoms called follicles.
Although the tubes may contain some other structures, for the purposes of our discussion, the most important features are the tubes themselves, and oil producing structures called sebaceous glands. The sebaceous glands discharge sebum, an oily substance, into the hair follicles. In acne, excess growth of the lining of the hair follicle combines with sebum and a protein called keratin, to cause blackheads. The blackheads block the flow of sebum from the hair canals, and cause mechanical irritation to the follicle. A bacterium called Propionibacterium acnes breaks down trapped oil, producing fatty materials that induce inflammation.