All acne is a disorder of the gland in the body that produces sebum. The oily substances that the body uses to keep the skin and hair moisturized. The location of this particular gland (known as the sebaceous gland) are on the face, neck, back and chest.
During the teenage years, the sebaceous glands enlarge and the production of sebum is increased under the influence of hormones, also called androgens. In normal circumstances the Sebum produced by the sebaceous gland comes together with cells being sloughed off within the hair follicle and fills up the hair follicle. When the follicle is completely full, the sebum is released, thinning out over the surface of the skin to give the skin an oily appearance. When this process works correctly, the skin is moisturized and remains healthy.
However when hair follicles become obstructed by trapped sebum, the cells that are normally sloughed off become sticky, plugging up the follicle. This process is called comedogenesis, and is responsible for most of the minor acnes such as blackheads and whiteheads.
Some of the causes for the more serious acne is caused by bacteria known as Propionibacterium acnes. This bacteria is a normal inhabitant of the skin and uses sebum as a nutrient for its growth. Due to increase levels of sebum during puberty, the level of bacteria also increases. The presence of the bacteria attracts white blood cells to the follicle.
These white blood cells produce an enzyme that damages the wall of the follicle, allowing the contents of the follicle to enter the lower part of the skin. This process causes an inflammatory reaction seen in the different types of major acnes such as papules, pustules, and nodules. The cause of the pain relating to these acnes are due to the bacteria producing free fatty acids. This also increases the inflammatory process in the follicle.