Acne is caused by the hyperactivity of the oil glands that excrete oily substances onto the skin.
 The oil glands of people with acne are very sensitive to normal dose of testosterone, a steroid hormone, which is usually present in both women and men.
Testosterone in people disposed to acne makes the sebaceous glands produce more sebum than usual. At the same time, the dead skin cells lining the openings of the hair follicles are not shed properly and clog up the follicles.
These two combined actions cause the increase of the oil in the hair follicles. This causes whiteheads and blackheads to form. For some people, their acne does not progress beyond this stage.
However in other people, the build-up of oil in the hair follicles creates an ideal environment for a bacterium called Propionibacterium acnes to grow.
Propionibacterium normally exist on the skin but when this ideal environment is disturbed, they increase. This bacterium provided for the sebum and produce substances that cause a reaction from the immune system of the body. This inflames the skin and creates the redness associated with spots.
The more severe inflammation is in case when the cysts are under the skin's surface. These acne cysts can rupture, diffusing the infection into nearby skin tissue. This often results scarring.
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